text:
Blender Python: Running multiple timers
I have a bit of a weird problem that I simply cannot seem to get around. I want to run 2 timers, each set to a different interval.
The problem that I'm having is that both classes receive each others 'TIMER' event! I think that this is really weird, as one would expect the timer event to be constrained within the class it's created in.
After hours of DuckDuckGoing, I found this forum post: https://blenderartists.org/t/how-to-distinguish-timers-when-running-multiple-modal-operators/601432/7
But it didn't help much, basically stating that it's impossible, + it's from 4 years ago, maybe something has changed.
Am I looking at this the wrong way? Maybe I don't really understand Blender's paradigm here, anything that can help me get on the right track would be really appreciated, thanks!
I created a demo blender file showing my problem: https://keybase.pub/peterwilli/StackExchange_Files/TimerProblem.blend
Just open with Blender and look at the console (open blender from the console in Linux) and run timer1.py and timer2.py, what you see is that both timers run each 1 second, but if you run both, both of them run practically twice as fast, taking each other's event.

The only way is using threads. Did you test that?

@yhoyo how would that work using threads? Would I still be able to redraw the 3D view? (I'm using timers to draw a HUD in the Blender editor)

Application Timers
Blender 2.8 has a new API to run functions in specific time intervals.
Run a Function every x Seconds
import bpy

def every_2_seconds():
    print("Hello World")
    return 2.0

bpy.app.timers.register(every_2_seconds)

Move an object every second
import bpy
import functools

def move_obj(ob):
    ob.location.x += 0.1
    return 1

bpy.app.timers.register(functools.partial(move_obj, bpy.context.object), first_interval=1)

Similar but passing object time axis and disp
import bpy
import functools

def move_obj(ob, axis, dist, sec):
    print(ob, axis, dist)
    ob.location["xyz".index(axis)] += dist
    return sec

bpy.app.timers.register(functools.partial(move_obj, bpy.context.object, "x", 0.1, 1), first_interval=1)

bpy.app.timers.register(functools.partial(move_obj, bpy.context.object, "y", 2, 10), first_interval=1)

bpy.app.timers.register(functools.partial(move_obj, bpy.context.object, "z", -0.1, 2), first_interval=1)

On a few quick tests it appears that the context, if passed to the timer like above is restricted, has no "object" attribute for example.

A friend just told me the same thing, I just downloaded Blender 2.8, too bad that the templates are still using the old version, I'll try to port a tiny bit and mark as valid answer if it works.

Thanks! It worked, I thought it was going to be an ordeal to port the whole script to Blender 2.8 but it wasn't so bad after all.
I never saw the new GUI it looks and works really well.


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Modify the size and location of the Rigid Body Collision Object
Maybe I'm just spoiled by Unity3D, but I would like to reposition and resize the Rigid Body Collision Object of an object in my scene. Is there currently an established method to accomplish this?

In Unity3D, you can adjust the x and y positions as well as the scale of the collision object.
Adjusting the collision margin and collision shape do not produce the desired result in Blender 2.78.
A thanka you.
*Updated Partially to my Satisfaction:

I was able to change the position of the rigid body object relative to the collision object in edit mode which persisted into object mode. However, the ability to scale the collision object remains elusive. It does appear I accomplished one iteration of upscaling though.

Related: https://blender.stackexchange.com/q/107231/28015

You can not resize the collision box itself, but you will notice that if you scale your object your collision box will scale as well.
To customize the collision box:

Scale your object in Edit Mode to fit the collision box.
Note the scale factors on paper and take the inverse of those numbers by calculating 1/x.
Then scale your Object by those Factors.

You can also do this with translation by translating in Edit Mode to fit the collision box and doing the inverse in Object Mode
Notice that this will work perfectly for cubes, but if you want spheres you have to keep them spheres. You can not turn spheres into ellipsoids.

You cannot move them. From the Blender manual (emphasis added):

Primitive Shapes
These are best in terms of memory/performance but do not necessarily
  reflect the actual shape of the object. They are calculated based on
  the object’s bounding box. The center of gravity is always in the
  middle for now. Primitive shapes can be shown in the viewport by
  enabling Bounds in the Object ‣ Display panel.

Use a mesh shape to get more precision:

Mesh-Based Shapes
These are calculated based on the geometry of the object so they are a
  better representation of the object. The center of gravity for these
  shapes is the object origin.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


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Access Object's Keyframe Data via Python
The goal is to change the hue of objects based on the difference between the frame when the object is made visible to the scene renderer and the frame_current.
What code will allow me to access the frame number of an object's visibility keyframe? Something like:
import bpy

objs=bpy.data.objects[0:-3]      #select multitude of objects barring a camera,
                                                                     # light, and curve
scene=bpy.context.scene
endF=scene.frame_end
currentF=scene.frame_current
while currentF != endF:
    for o in objs:
        start=o.visible.frame # <-??              #set variable for the frame number
                                                  # when each object is made visible
        hue=o.material.diffuse.color        #set variable for hue of object's
                                                                         # material

    #set hue based on difference between current frame and visible frame
        if currentF-start==1: hue=0x6E00E7

The line of code I really need help with is marked with "# <-??", i.e., line 12.

Solved.
It works now.
import bpy
objs=bpy.data.objects      #make list of all objects in scene
scene=bpy.context.scene
endF=scene.frame_end
currentF=scene.frame_current
keyframes=[]
meshObs=[]

for o in objs:
 if  o.type == 'MESH' and o.animation_data !=None:
     fc = o.animation_data.action.fcurves.find('hide')
     keyframes.append([kfp.co[0] for kfp in fc.keyframe_points if kfp.co[1]==0][0])
     meshObs.append(o)

The following will give you an array of all the frame numbers (as float) where the visibility is True
fc = o.animation_data.action.fcurves.find('hide')
frameNos = [kfp.co[0] for kfp in fc.keyframe_points if kfp.co[1] == 0]

you can find the previous one from the current with
start = max([kfp.co[0] for kfp in fc.keyframe_points if kfp.co[1] == 0 and kfp.co[0] < currentF])

Thank you, Blender Dadaist. That part works perfectly now. I used the code in your first code block, edited to invoke append method. These are the start frames which is all I needed. I don't understand what the code in the second code block is supposed to do.

Also, I added [0] to extract the value from it's coordinate array in kfp. Now, I have float values for keyed frames to compare with the float value of the current frame.

I just thought you want the 'visible' keyframe immediately preceding the currentF in the variable 'start' (in case you have multiple keyframes that turn on the visibility). That's what the second codeblock does. But glad that you were able to solve the problem :)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What is the Easiest way to Animate the rigid body properties of a large group of objects
I would like to animate 500 or so shards to be "animated" rigid body at frame zero and "dynamic" at frame 550. Do I really have to set a keyframe for each individual object or is there a way to animate that rigid body property as a group?
The shards are in a group, but it appears that the rigid body for a group of objects can only be set, not animated. I've tried using an empty parent object to no avail.

[Select the rigid body object and copy their properties (except for animated).]

Select all rigid body object to be modified.
Alt click on the Animated property. This will change the property for all the selected object to the same value. Now all object have animated enabled.
Use this script to key the property on all of them.

import bpy
sel = bpy.context.selected_objects
for ob in sel:
    ob.rigid_body.keyframe_insert(data_path="enabled")
    ob.rigid_body.keyframe_insert(data_path="kinematic")

Now all objects are keyed.
To remove all Animated keys on a frame, execute the script but replace keyframe_insert with keyframe_delete.

Thank you so much, Leander. Please add the following line to your script, and then I will mark your answer as 100% helpful by clicking the checkmark:
ob.rigid_body.keyframe_insert(data_path="enabled")

@silvermanj7 You're welcome, I have edited the line, feel free to edit it yourself, if I misunderstood

oh i didn't realize i had the power. thanks again. :))

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Updated to v. 2.8; Why, now, all animations work except one in v. 2.79 .blend?
I made an animated scene with Blender version 2.79 and then updated to 2.8.
 The animations for my cameras and second character work just fine. But, for some reason, the first character is not animating at all. The keyframes are still there.
 Am I missing some setting that's preventing the animation of the first character? Perhaps I have to retro-date to v. 2.79 to save the .blend in an alternate state, perhaps, with no objects selected, then try again in v. 2.8. Hopefully, there's an easier fix.

Don't jump versions

I fixed it by unparenting the character from the ground plane object. The configuration worked in 2.79 but not in 2.8 for some reason. Oh well, easy fix.


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Keymaps within an add on's preference panel
I am learning to build a simple add on executed by shortcut keys. I have the add on working with a keymap that I defined upon registering. The user can change this keymap from Preferences > Keymap and then searching for the add on by name. But I would like to allow the user to change that keymap from within the add on's preference panel directly.

I have a lot of add ons that do this (like Cablerator, below). It appears to be drawing the exact same UI from the Keymap preferences, but I can't seem to find resources or examples of how this is done.

Does the API expose some of this easily that I can use? How are folks doing this?


text:
Weird pixelation effect on backdrop
[Reupload with more information]
Hi!
I have a problem, you can see a weird pixelation effect on the backdrop of these renders. I don't know what causes them. I have a simple beveled backdrop with a beveled light setup. I use cycles and attached the blend file at the bottom.
Image:

Pixelation effect highlighted, because it is hard to see in some light conditions:

maybe it's your denoiser?

What blender version you use? In Compositor is probably Denoiser node that is not recognised by 2.9x or 3.0 ... so it is Cycles X? BTW ... rendering without Compositor it is not pixelated ... so probably issue related to this node.

I'm using 2.92.0, but the weird thing is that I see this without the Denoiser node too, unlike you.

Hi :). Are you're by chance rendering with both CPU and GPU? That might sometimes cause this.

@JachymMichal Yes, actually I am. I will try with only GPU after this render. (brb in ~30 minutes)

@JachymMichal Yes, rendering with only GPU fixes the problem. (But sadly doubles render time on my potato pc.) Could you please write an answer instead of a comment so I can flag it as answered?

Hi :). I suggest to link your question with an older thread, just to keep the site organized. However, you can also report this behavior as a bug :).

Okay, thanks for the help!


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Smoke doesn't seem to have initial velocity
I've been following this tutorial on how to make a simple explosion, I am using the same values, but I don't get the same effect.
It seems like my particles have no initial velocity.
Do you know what could cause this problem?
Updated .blend file:

His explosion:

My explosion:

My explosion after James' tips:

I had the same problem. Increasing the source under Initial Velocity seems to help. I set it to 25 and it looks similar to his results.

To be honest, by now I forgot about this project, but yes, that works.

[Edited per our conversation below]...
I think blender is indeed having a problem with its cache.
Aside: I see you have disk cache vs. memory cache for Plane.001 vs Plane.002; perhaps your just trying various combinations.
Try:

deleting your 'blendcache_smoke_test' and 'cache_fluid_4b85f272' cache folders
In scripting, click on New and cc/paste and run the following script (also in the attached blend file) that should create things in the correct order (finding and running all PS sims before Fluid sims).

import bpy
import time

bakedItemCount=0
startTime=time.time()
for scene in bpy.data.scenes:
    for object in scene.objects:
        for modifier in object.modifiers:
            if modifier.type == 'PARTICLE_SYSTEM':
                print("Baking particles for ", object.name)
                override = {'scene': scene, 'active_object': object, 'point_cache': modifier.particle_system.point_cache}
                bpy.ops.ptcache.free_bake(override)
                bpy.ops.ptcache.bake(override, bake=True)
                bakedItemCount+=1
    for object in scene.objects:
        for modifier in object.modifiers:
            if modifier.type == 'FLUID':
                if modifier.fluid_type == 'DOMAIN':
                    print("Baking fluid for ", object.name)
                    object.select_set(True)
                    bpy.context.view_layer.objects.active = object
                    bpy.ops.fluid.bake_data()
                    bakedItemCount+=1
            elif modifier.type == 'CLOTH':
                print("Baking cloth for ", object.name)
                override = {'scene': scene, 'active_object': object, 'point_cache': modifier.point_cache}
                bpy.ops.ptcache.free_bake(override)
                bpy.ops.ptcache.bake(override, bake=True)
                bakedItemCount+=1

endTime=time.time()
duration = int((endTime - startTime)+.999)
print( bakedItemCount, ' items baked over ', duration, ' seconds')

Frame 16 rendered with max samples = 16 to reduce render time:

Hi James, I've tried your suggestions, but it still looks almost the same. The smoke that the particles spawn don't seem to have any velocity, and are just a puff of fire and smoke. I have no idea what could cause this.
I've updated the post with a new image and the new blend file. (now on Blend-Exchange)

I actually think that this is a bug, I've been doing some tests. Here is my test scene. If you bake the weird domain first, both simulations will have no initial velocity, but if you bake the correct one first, both will look good. The difference between the two is the flow source of the cube, the incorrect is from the volume and the correct is from the surface. Do you think I should report this somewhere?

@Matthias -- you would certainly have to bake the PSs first, as then the PS drives the position of the particles that the fire'n'smoke are based upon.  I do not think that is a bug per se: it is a procedural workflow that is perhaps a bit arcane.   Have you reviewed the tutorial to see if you had missed a step or if that was not covered?  Does my video look anything like what you are expecting?

Yes, I've baked the PSs, I changed all the thing that you've suggested. And also yes, I've reviewed the tutorial step by step. And the problem is that I can't really see, because my video looks the same at 32 resolution divisions. I think that if you'd render one frame at like 192, you'd get the same effect as me. Like the smoke that the particles spawn don't have velocity and are technically just a static sphere with a geometry inflow, not like in the tutorial.

If you don't know what I could do to change this, maybe I'll follow the tutorial again tomorrow, but with an older version of blender. Maybe that'll help to discover the root of the problem.

@Matthias -- your simulation and last frame are set to 100, so did you mean to render frame 92 and not 192 (where console says Cycles error: unexpected smoke volume resolution, skipping)? Okay I redid with your orig file and there is no fire/smoke rendering, while in my blend there is... we should compare and look for differences.  You'll see I supplied mine.

@Matthias -- It appears to be a caching problem.  I was able to recreate the problem of no smoke.  I edited my above answer to mention zapping your cache folders, and running sims in scripted order.

So I watched the tutorial again, using the same version as him, and it still looks the same. I run the scrips and deleted the cache, still the same. Actually your first image kind of looks like mine, but it is still completely different from what the guy in the tutorial achieved. To be honest, I'm getting tired of this problem, and I think I'll just give up. I don't know how he achieved that explosion, you couldn't achieve it, I couldn't, I don't think anybody could. I won't close this thread in case some particles or VFX pro stumbles upon my problem. But all in all, thanks for trying to help.


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Automate UVMap and Baking on object list
I'm trying to generate and bake a new UVMap for each sub objects ( 4 piece_*.).

So i made this python script :
bpy.ops.object.select_all(action='DESELECT')
for obji in bpy.data.objects:
    obji.select_set(False)

for obj in objs:
     if obj.name.startswith("piece"):
        print("ForLoop objects " + obj.name)
        image_name = obj.name + '_BakedTexture'
        img = bpy.data.images.new(image_name,2048,2048)
        bpy.context.view_layer.objects.active = bpy.data.objects[obj.name]
        obj.select_set(True)
        #bpy.context.active_object = obj
        print("Debug Active Object " + bpy.context.active_object.name)
        bpy.context.object.update_from_editmode()
        for mat in obj.data.materials:
            mat.use_nodes = True #Here it is assumed that the materials have been created with nodes, otherwise it would not be possible to assign a node for the Bake, so this step is a bit useless
            nodes = mat.node_tree.nodes
            texture_node =nodes.new('ShaderNodeTexImage')
            texture_node.name = 'Bake_node'
            texture_node.select = True
            nodes.active = texture_node
            texture_node.image = img #Assign the image to the node

        #           bpy.context.view_layer.objects.active = obj
        bpy.ops.mesh.uv_texture_add()
        bpy.context.object.data.uv_layers["UVMap.001"].name = "UVBake"
        #bpy.context.object.update_from_editmode()
        bpy.context.view_layer.objects.active = bpy.data.objects[obj.name]
        #bpy.context.area.type = "VIEW_3D"
        obj.select_set(True)
        #bpy.ops.mesh.select_all(action='SELECT')
        bpy.ops.object.editmode_toggle()

        bpy.ops.uv.unwrap()
        bpy.ops.object.editmode_toggle()
        bpy.context.view_layer.objects.active = bpy.data.objects[obj.name]
        bpy.ops.object.bake(type='DIFFUSE', save_mode='EXTERNAL')
        img.save_render(filepath=exportFolder + "\\" + obj.name + '_baked.png')
        for mat in obj.data.materials:
            for n in mat.node_tree.nodes:
                if n.name == 'Bake_node':
                    mat.node_tree.nodes.remove(n)

        #bpy.ops.object.editmode_toggle()
        print("end process " + obj.name)
        obj.select_set(False)
        bpy.ops.object.select_all(action='DESELECT')

What is strange first , is that it's working only if i select the first piece so I guess all my treatment to select the object is not working fine.
And after that, it generate actually the 4 same textures so it seems that the selection is still on the first piece
EDIT :
I add some logs and it's so strange :
Got GET: {'type': 'ping'}
Got POST: {'type': 'script', 'path': 'd:\\Users\\x.larrode\\Documents\\Blender\\laRedoute\\UVObj.py'}
ForLoop objects piece_100_2_1_1
Debug Active Object piece_300_3_2_1
Info: Baking map saved to internal image, save it externally or pack it
end process piece_100_2_1_1
ForLoop objects piece_200_1_1_1
Debug Active Object piece_300_3_2_1
Info: Baking map saved to internal image, save it externally or pack it
end process piece_200_1_1_1
ForLoop objects piece_300_3_1_2
Debug Active Object piece_300_3_2_1

So as you can see the Active Object it's always the one i selected before lauching the python code...

So if i select Nothing, i come across a problem of context :
File UVObjAllInOne.py", line 63, in
bpy.ops.mesh.uv_texture_add()
RuntimeError: Operator bpy.ops.mesh.uv_texture_add.poll() failed, context is incorrect
Any ideas?


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How to fill particular areas in texture paint?
I tried to Google this for hours but couldn't find how to do this. I have an object with a texture that has a completely closed black circle. See this example:
What happens it that if I try to fill my inner circle with orange, the whole circle fills. I wanted fill only the inner circle (similar colors). I was hoping if someone could tell how to accomplish this. Thanks!

You can use the UV Image Editor Fill tool and play with the threshhold settings to see how well the fill works without spilling into the area around the colored area.

Thanks. But what if your UV map lies outside of the closed loop? I forgot to add to the question, sorry. Like this: https://imgur.com/a/Yn5T5Db

You can paint a new boundary in the UV Image Editor to close that area - and then drop the fill into that enclosed space. BUT if you really want a lot of really good control, please look into using the Mask Tool in the 3d viewport - you can literally paint masks as if they are photoshop layer masks to isolate areas in the 3d view without having to paint directly on your color map.

I opted for closing the loop in the UV image editor, thanks!


text:
3d Printing Problems
I have some problems when I try to 3d print my project, so I'll be as specific as possible.
I first created this mask, and applied a solidify modifier to it:

The first time I exported as .stl, but it showed up blank in the 3d printing software, Cura. I then applied the solidify modifier, yet it still was blank when imported.
I then tried to export as .obj, which worked fine. I could see it in Cura. I began the 3d printing, using an ultimaker2, yet it did not seem to be working. It started the printing but ended up just moving the material around.
One thing to note is that when looking at the Layers in Cura, it seems that even with the solidify modifier, it looks infinitely thin, only showing some thickness. Why would this be? Could it be a problem with the export options, or with my mask itself?
Here is the project file if anyone could look at it: https://drive.google.com/file/d/0ByCsi4JV6Yv1WXBfSkJlTnd1SUU/view?usp=sharing

you might be interested in the proposed 3d printing site of StackExchange

It seems that you must have a certain amount of reputation on that site to ask a question, yet I need an answer quite soon. To the best of my knowledge this is a problem with me and Blender, as I am only a beginner and am most likely missing something quite simple.

If you really want to learn, upload a .blend file so some of us can have a look at it. http://blend-exchange.giantcowfilms.com/ .

Here is a link to the project file: https://drive.google.com/file/d/0ByCsi4JV6Yv1WXBfSkJlTnd1SUU/view?usp=sharing

The usual culprits for this sort of thing are as follows:

Too small (scale) : most 3d slicing software has their units set up so that blender should export .stl's at .1 scale.  Otherwise, the object may be waaaay to big. or waaay too small. Try playing with the export scale and the object scale and see if you have any luck.

Too thin : the parallel problem to the scale issue is that if it is too thin, the object will not slice properly.  There is a minimum thickness the printer is capable of, and the slicer will exclude things that are too thin.
Inverted normals : if the normals are not set the right way, the slicer will not be able to detect the solidity of the object.
Non-Manifold :  Your object must be closed, or the slicer will not be able to detect the solidity of the object.

Due to your description, it sounds like one of the last three.

One other option is to use a free 3rd party tool like the plugin from 3YOURMIND https://www.3yourmind.com/3d-print-add-on-blender so that you can see exactly where the errors are occurring when preparing the file for 3D printing with specific materials. You will be able to see if the file is simply too small, or if specific walls are two thin. The software will also do many of the basic repairs (fixing inverted walls, connecting edges, etc) for you.
Then you can download the file to do your printing, or use one of the connected 3D Print services to create the model for you. I find that especially being able to see where exactly the model has the thin walls to be a big time saver!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Circular Light Source Causing Speckles in Cycles
(Blend file is in the comments)
I am trying to create a stage in the Cycles renderer. I have modeled a stage light that looks like this. It has a circle with the emission shader to act as a light source

However, when I try to render the scene, speckles appear on the stage:

As you can probably tell, the more samples, the more dots, but they become smaller. Given that it took a couple minutes to render with 1024 samples, I don't simply want to set the samples to something ridiculously high like 16,000. Does anyone know what's going on?
(The Wooden Floor uses the default Diffuse BSDF Shader with an input from an Image Texture, mapped by a UV texture coordinate. I would put an image but I can't upload any more)

BLEND FILE: http://blend-exchange.giantcowfilms.com/b/866/

I enabled multiple importance and there are still speckles. I think they're called fireflies.

I figured out the problem: I needed to turn up "Clamp Indirect." The Article Here has a bunch of solutions, and the only one that worked for me was the 6th option.


text:
Export object to a 3ds file error
I want to export the height-map to a .3ds file. I've tried doing this with export function and get the error

blender object r cannot be written into a 3ds file.

I have read that this can be caused by having too many vertices (65536) and after much decimating I am now bellow this but I'm still getting the error. Is there any other cause for this error?
Screen shot of height-map:

Link for download of .blend file (http://1drv.ms/1R7sQLq)

Attaching the file in question would definitely help resolve your issue. If we could test it locally, answers would be more efficient for such problems.

Iv uploaded it to a onedrive account, thanks for your offer of help. I had assumed it was something obvious I was missing so it would not be needed.

Oh you never know , I was running version 2.73a and had my models export out without any normals information , not until the developer at shadermap ran some low level test on it.

The solution ...
I found out that your model have a total of 112,330 triangles.
and on the wiki it states that 3ds have these shortcomings:

All meshes must be made of triangles.
All texture filenames are limited to the 8.3 DOS format.
The number of vertices and polygons per mesh is limited to 65536.
Accurate vertex normals cannot be stored in the .3ds file. Instead "smoothing groups" are used so that the receiving program can recreate a  representation of the vertex normals.
Object, light and camera names are limited to 10 characters. Material names are limited to 16 characters.
Directional light sources are not supported.

WHY?
So why was it having problem exporting even though you have the faces count
at 24,000 and vertices at 56,000 range? Both numbers comply with the 3ds format's limitation. The problem is that all the faces needs to be triangles
, the export operation convert all non triangle surface to triangles before saving. Moreover, you can test this. If you do CTRL + T and triangulate your mesh in edit mode you will realise that your mesh exceed that limitation.
After triangulation it sits at 112,330 faces! Which is equal to the number of triangles. In the case of 3ds format, the triangles count is the number we want to keep an eye on.
HOW?
Notice the word per mesh ... that is our key to exporting high poly mesh.
What I did was break up your mesh into 3 portion and then export them in
one single 3ds file.
DOWNLOAD THE BLEND FILE HERE
Try exporting the file and reimporting into blender should give no more problems
now.
A Little History of Polygon
A long time ago in the early days of CGI, polygon refers to triangles.
It's not until much later, more artist prefers to work with 4 sided polygons
then 3 sided ones. (Less clutter on screen, better work flow!) Sometimes when we read about some legacy format that were created in the 1980s, polygon may very well meant triangles!

Thank you, could I ask how you went about breaking up the one mesh into many?

I did a simple selection in edit mode. You can use any select mode you choose. When you are done selecting, hit keyboard "P" and choose selection , this would copy the selection and separate it into another standalone mesh. Very simple to do really and you could typically join it back together in any other 3d packages.

Thank you, I was able to reproduce what you made following your instructions. Thanks again!


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pink texture on imported model. How to re-link the texture?
Once again, the pink texture.
Here are the steps I am following:
Download a Blender-specific file from Kitbash 3D
Unzip into a clean folder. Two files show, a Blender file for the Kitbash buildings and a folder of KB3D textures.
Run Blender, open the Kitbash buildings file. Textures are pink.
Go to File >> External Data >> Find Missing Files
Locate texture folder and click on Find Missing Files
This opens the folder, listing the texture files. Click on Find Missing Files again
Result - NOTHING!
What am I doing wrong? I've followed the recommended procedure, but it just doesn't work.

Hello and welcome. Please use a descriptive title that reflects question content

Check [ask] to learn more about asking questions. Don't forget to come back to check for answers sometime and mark as accepted if one solves your problem.

If you look at the file paths they are most likely not relative in the original blender file hence they wont be found. The way the blender file was packaged probably wasnt correct.

But what is the correct way to quickly re-link lots of textures which are all in the same folder?


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Why is subdivision surface behaving like this?
I'm wanting to 3D print my object- so I'm looking for a literal way of smoothing.. I want this object physically smooth while maintaining creases and negative space, like this:

However, Subdivision surface is behaving like this. Why? And how do I fix it?

Thank you! :)

This will happen if you don't have enough geometry on the large faces with the cut-out to support the subdivision operation.  Consider these two objects:  both have the same shape cut out of a flat disk, but on the left, only a few edges have been used to connect the cut-out to the outside of the disk, while on the right, the same shape has been cut out of a whole grid of geometry:

and here's what they look like with a subdivision surface modifier added:

Note that the geometry doesn't have to be perfect.  Even pretty crude geometry will usually work:

You'll need to add a similar amount of geometry on the faces with your heart cut-out.  The heart shape might make it a little harder.  At the sharp parts of the curve, you make find it necessary to introduce duplicate overlapping or nearly overlapping edges:

Thank you so much that makes total sense!! I think it was the underside giving me trouble.. I got lazy and filled the whole thing in one big section, rather than individual pieces. Learnt my lesson lol

A method I found to fix this (this isn't the 'right' way of doing it albeit- but posting to potentially help anyone else!)..

alt+click the section of edge you want (in my case, the heart)
shift+D to duplicate
Press P and choose the new object from the top-right menu
fill it, extrude it upwards and create a boolean on the original object with it
use subdivision surface! (It won't fill in the hole because of the boolean :)


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Why is my fire simulation blocky even with 5000 resolution divisions?
For some reason, my fire simulation is really low resolution even if i set it to a crazy number of divisions. why is this happening?

here it is with 5000 resolution divisions

here it is rendered out

It would be ill-advised to display the full resolution in the interactive viewport. How does it look rendered out?

Oh ... What kind of setup has to be used to sim res 5000? ;) There matters what is the longest edge of your domain to say if it is or is not enough.

my setup for baking 5000 res is my mac air. that shouldn't be possible but somehow it is working?

also, i just rendered it out, it looks the same, quite blocky.

also i have adaptive domain on, not sure if that helps

perhaps the answer is to do 100000 resolution :) also sorry i sent so many comments

How huge is this domain?

provide your blend file - your informations are too modest

Hi, thanks for the post.  This question is getting close votes because it lacks details or clarity.  You've made some comments where you give more information, we prefer that you edit your question to include these details (and more).  Once you've made your edit, your question will be automatically queued for review to be reopened.

@supercriticalpotatohead People keep asking how huge your domain cube is. Usually I make smoke simulations with divisions of 150-250 or 500 if I want them highly detailed. So again, if this is 5000, what is the size of your domain? And for the rendered image, this looks like Eevee to me. Are you working in Eevee or Cycles? If Eevee, what Render Settings for Volume have you got? As Allen said, your question is getting close votes because it's lacking of details what you've actually done.

I have found the solution, i looked at the size of the domain like you told me to and it was actually huge, so i scaled it down and now it works fine.


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Lighting in Cycles is not working properly
When I try to work with Cycles my lighting doesn't show up and I see nothing in my viewport.

But when I switch to EEVEE everything works properly:

But when I try to render I get my model lighted but not by my light set up:

I am pretty new in Blender and I know I must be doing something wrong but I have no idea where is the problem.
You can download the file in this link https://drive.google.com/file/d/1b6gHCYrIMrZFlJPKN0PrO1KmQaP2eyqV/view?usp=sharing

Can u please provide your blend file?

There it is!! thank you!!  https://drive.google.com/file/d/1b6gHCYrIMrZFlJPKN0PrO1KmQaP2eyqV/view?usp=sharing

On the top right corner there is a play button:

This enables/disables viewport rendering, clicking it should start previewing your viewport render on cycles

Thank you Zophiekat!! you are right, once I disable the play button I am able to see my render on cycles in my viewport. But my light setup is still not working with the skin texture, it is as if the skin texture were not affected by the lights, but my lights are working in the eyes textures. Do you know what it could be the problem? Thank you very much for your help!

there are lighting differences in eevee and cycles, make sure your light is set up to be able to affect diffuse. or make sure the skin material has the output node set as "All" or "Cycles". you could also look at the meshe's visibility tab and see if some shading stuff is disabled, take note this tab is only visible with cycles


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Blender Guru's Realistic Earth - problem with adding blur
I have been following this guide - https://www.youtube.com/watch?v=0YZzHn0iz8U - to create earth. Got to the section on add the blur to the composite (at 14:12 in the video), I only see it when I have the image is in the bottom of the Alpha Over and the blur in the bottom. But this results in the clouds and surface to get blurred. Can you advise on this?

Would you mind clarifying: 'I only see it when I have the image is in the bottom of the Alpha Over and the blur in the bottom. But this results in the clouds and surface to get blurred.' I'm not quite sure what you mean here. Can you explain clearly what you are expecting vs. the result you are getting?

In the guide the surface of the Earth is visible with a thin line on the edge to show the atmosphere. I have the same settings and the whole earth is covered in blue haze and not the edge,

You have the connections on the Alpha over node backwards.
Switch the inputs so the Color Ramp is plugged into the top, and the original image is plugged into the bottom.
The Alpha Over node is used to add the original image on top of the colored blur from the Color Ramp. The original image therefore needs to go into the bottom of the Alpha Over node.
If you find you are not getting as much haze as you like with this setup, try increasing the X & Y values for the Fast Gaussian blur.
Edit (as per comments):
I have downloaded your file.
Checking your materials, I found a small issue you should be aware of.
The Color Space for some of your textures is set to 'sRGB' when they should be set to 'Non-color':

Texture nodes are set to 'sRGB' by default, but only textures that are contributing to the Color input of your Shader should be set to sRGB.
Every other texture (i.e. Roughness, bump, normals, displacement, etc.) should be set to Non-color.
As for your issue with the atmosphere, if I understand correctly your problem is that you cannot see enough of the atmosphere when compositing.
I have replaced the smaller materials in your file with the hi-resolution materials from the BlenderGuru YouTube video linked in your question.
The following screenshots are taken from your file. The only changes I have made are changing the Texture Space from sRGB to Non-Color for some of the textures in your Surface and Clouds materials, and replacing the textures with the hi-resolution versions.
Here is an example using Blender Guru's suggested settings:
Fast Gaussian Blur Amount: 1%

Result:

To increase the atmosphere, we can increase the Fast Gaussian Blur Amount:
Fast Gaussian Blur Amount: 5%

You can also experiment with changing the size of the 'Atmo' object before rendering (BlenderGuru suggestion 1284m).
Atmo Size: 1300 m
Fast Gaussian Blur Amount: 1%
Result:

Notice that this gives a more solid look to the atmosphere close to the earth, which might be what you are looking for, I'm not sure:

Again, you can mess with the amount of Fast Gaussian Blur:
Atmo Size: 1300 m
Fast Gaussian Blur Amount: 3%

Here is a link to your file with the updates I have made.
You will need to add the textures back into your materials (make sure the Color Space remains as 'Non-Color' for the Roughness and Displacement textures!).

Edit 2 (as per comments)
To get the plane object with the stars working correctly, you need to complete a few steps. Firstly, we need to position it correctly in the scene.
Here is your scene from top view:
Note: I scaled up the camera object so it would be visible

Reposition the plane as so:

You can also scale/rotate the plane from camera view (Numpad 0) to check that it is positioned correctly:

Next, we need to move the Plane object to a new Collection. This will be important for the next step.
To do this, select the Plane object and press M > New Collection. Name the Collection 'Stars'.
You may also want to take this opportunity to rename the Plane to 'Stars'.

Next, we need to set up a new View Layer.
The reason the Stars object is messing up your compositing nodes is because it removes the transparent background.
We therefore need to do two renders, and composite them together.
The first render will be of the Earth without the stars, the second render will be the stars without the Earth.
First, find the View Layer section in the top-right corner of the screen:

Rename the current View Layer to 'Earth', and disable the Stars collection using the tick box:

Add a new View Layer using the icon to the right and name it Stars.
Disable the collection named 'Collection' (containing the Earth, atmo, etc.):

Now when we press render, the 'Earth' View Layer will be rendered first, followed by the 'Stars' View Layer.
We will have access to both renders in the Compositor.
Finally, back in the Compositor, add a Color > Mix node, and set the type to Add.
Position the Mix node between the Alpha Over node and the Composite (and/or Viewer) node:

Duplicate (Shift+D) the Render Layers node, and change the layer from Earth to Stars:

Plug this Render Layers node into the bottom socket of the Mix node:

Here is an example with this node set up.
(Note: I made some changes to your stars material to introduce some color, and some variation in brightness/size of the stars. Check the file attached below if you want to see the node setup for this material).
Rendered at 250 samples:

You may also want to add some Fog Glow to your stars using the Filter > Glare node:

As a final tip, if you are making changes to the material on your Stars object, there is no need to render both View Layers again. You only need to re-render the 'Stars' View Layer. You can do so using this button on the Render Layers node in the Compositor:

If this answer helped you, I'd appreciate it if you could accept the answer using the tick mark on the left, so that others who are suffering the same problem can find this solution easily.
Here is the finished .blend file:

I made the changes you suggested. The edge of the earth is still has a hard edge.

Could you please share your .blend and I'll take a look? Please make sure to pack the textures (File > External Data > Pack Resources) before saving and sharing.

how do you share a blender file?

https://blender.meta.stackexchange.com/questions/658/including-a-blend-file

Stripping all but one texture for the surface gets the file down to 76,406kb. Just too big for the exchange (original file is 111,566kb). with no textures its 937kb. is the no texture version ok for you?

Can anyone advise on this compositing issue?

It's difficult to help without your file. You have two options. You could resize the textures so they are not as large. Open them in an image editor (i.e. MS Paint/GIMP) and scale the image textures to 25%. Save the smaller images and use them in your .blend project. That should result in a small .blend file. Alternatively, upload the 76MB file to DROPBOX instead of blend-exchange, and share that link

Dropbox link: https://www.dropbox.com/s/kx57b09j5sfzs26/Realistic%20Earth%20tutorial%20smaller.blend?dl=0

I have updated my answer

@Mark_72 in the future if you need to add additional information regarding your question, it is best to add it into the body of your question as an edit so that it is visible to anyone who may wish to answer.

I think I can see the problem. You had hidden the plane I could see the atmosphere. But when I done a render with the plane there, but I had moved the camera, some of the atmosphere is visible but the bit the plane is not. Also I did not notice the Colour space change when adding the smaller textures.

In that case just move the plane to behind the earth. Select the plane and press 7 on Numpad to go into top view, then position the plane on the opposite side of the earth to the camera.

the plane is behind the Earth and the camera is in front of the Earth.

Answer updated with instructions on how to keep the stars

Thanks for all your help. Not used View Layers before. I am working on adding an object to be orbiting the earth and I can see how to add it to the scene.

Glad to help. Good luck with your scene

Looks likes good now.
Will leave off the plane as it is stopping the atmosphere showing. Shame I can't get any stars in the background.
Thanks for all your help.

This is not an answer, but a comment on an existing answer. Please comment it there, or edit the information into your initial question.

I have updated my answer with instructions on how to keep the stars in the background. Please delete this answer (which is not an answer), and accept my answer above, assuming it resolves your problem.


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how can I fix blender not responding after I activate default hair particles system? BLENDER JUST STOPS RESPONDING -Lenovo CORE i5 8GB RAM-
When I try to use Blender default hair particle system it just stops responding even though it has not used my entire RAM and CPU. Is there a way to fix this?
On -Lenovo IdeaPad S145 CORE i5 8GB RAM-

How long did you wait for a reaction? Does blender take up any cpu percentage during the "freeze"?

the CPU usage remains relatively low, it never goes over 20%

That's because in this case, blender uses only a single thread and not all of your CPU cores. What exactly are you trying? How many particles and children do you have? When exactly does your system seem to freeze up?

Emission (1000, 0 seed,) Children Interpolated ( Display amount 10, render amount 100) even with its default settings it still does freeze. what intrigues me is that it doesn't freeze immediately after creating the hair particles, it times it takes few minutes. at times can even groom the hair to the shape I want before it freezes. it does this with everything, when ever I try to create character hair or fur

Did you try different blender versions?
What display mode and render engine do you use?

I first noticed this when I was using 2.82, I thought maybe the blender version was the problem, upgraded to 2.91 still the same results. it does this in Solid View Cycles, I haven't tried Material or Rendered views since solid is less demanding compared to the two.

Hm... Then I am runnning out of ideas. While your PC is certainly not a beast of a machine, it should be able to handle that kind of work. I assume, your drivers are up to date and your machine is in good condition (no blocked air ducts or fans)?

I really really appreciate the help thanks a bunch. where you are right at this moment I am there. I tried everything my PC is up to date. but it is a small dent i'll work around the problem. Thanks again.


text:
Discontinuous large values in depth map
For my project, I save rgb frames (PNG format) and the depth maps (EXR format) for different camera views. The compositor setup I use is shown here  and I use Cycles.
When I read the raw depth values, for plane surfaces like paintings or glass surface the depth map has sporadic, or clusters of, very large values like 10^10 among a region of foreground pixels with low depth values.
Why does blender render these certain pixels as background, when they actually belong to a foreground object? This renders the depth map inaccurate.
Is there a better, accurate way to obtain depth maps from blender?
Edit: The link to a blend file where I saw this.

It's hard to say for sure without seeing the file.
But I believe you're probably seeing places where the reflections shoot off into infinity.
Let's think about glass, which is one place where you mentioned problems.  A ray either goes through the glass or reflects from the glass.  You can get vastly differing depths depending on which it does.  The depth needs to take into account the reflection for purposes of misting, DoF, etc (think a mirror).  But there's no sense in mixing depths-- you're not going to get something more right by averaging the depth through and the depth reflected, you're just going to get something completely wrong.  Blender has to pick between reflected depth and refracted depth, and where it changes its pick, you have a discontinuity.
What's the solution?  I've asked around and not heard any suggestions.  If you want your depth to a surface, you can render an Eevee depth map, which won't have this behavior.  You could also consider using multiple render layers, perhaps with material AOV outputs that would let you specify flat depth, reflected depth, or refracted/transparent depth.   But yes, these are frustrating solutions in that they can potentially add a lot of render time and complexity.

Thanks, this explanation makes sense. Regarding rendering depths with, possibly, Eevee, is it possible that it will introduce errors in other regions where I previously had not any errors? I.e, is eevee error-free?

Also, how does blender choose between reflected and refracted depth?

@VjayalakshmiK Eevee depth map and Cycles AOV depth material should be same, but untested.  Cycles probably choose between depths on the basis of which component (glossy, refraction, diffuse et al) has the strongest influence on the sample (mix glossy->refraction at 0.6 probably gives refracted depth.)


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Liquid Simulation How to Stop Interaction with Grid Floor
Honey undesirably and mysteriously interacting with the grid floor. I've tried unchecking the box for grid floor display to no avail. The honey sticks to the underside of the grid floor.
How can I bypass the grid floor here?
The rectangular, animated plates and the 3D plane are Fluid Obstacle objects.
I will provide any further information deemed necessary.
Thank you.

Grid Floor in Display rollout can't affect simulation in any way, it's just for visualization purposes. Fluid simulation can be stuck either in collider objects, too thin objects for current fluid resolution or in the end of fluid domain.


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How to make dynamic paint work with rigid body interactions during animation playback

I'm trying to dynamically wave paint a passive, rigid body, wave-modified plane canvas with an active, rigid body, sphere brush via dynamic animation playback.
The dynamic painting works when changing the location of the brush, i.e., the sphere, in object mode, but fails when the dynamic, rigid body animation is played in real-time, as you can see in the gif. Blender allows for a single interaction at the beginning of the animation, but then the sphere just rolls on top of the canvas without displacing any of its geometry during the animation.
I want to upload my blend file but don't know how.
Perhaps a shrinkwrap-modified plane to the canvas will work.
The brush only works with "distance from center" as the source which is set well above any collision margins.
I've tried applying the wave modifier to the plane to no avail. I've tried pretty much all combinations of settings for the dynamic paint and rigid bodies, even adjusting the render fps, to no avail.

I found a workaround that may be acceptable while sacrificing some dynamic behavior.
What I found out is that you can turn a rigid body simulation into a string of keyframes via a built-in function under the object menu in object mode called "rigid body" > "bake to keyframes".
I had realized that the dynamic paint seems to work only with a keyframed brush, but I wanted that authentic, physics feel to the simulation, thus the solution was to bake a rigid body simulation and then turn it into keyframes. Lastly, I removed the rigid body physics from the brush sphere, pressed play, et voila!

Hooray!


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Add a new mesh object while also specifying its vertices count during creation (in 2.8 and later)--yet how to edit that same vertex count afterward?
For example:
Object Mode!Layout!Add!Mesh!Cylinder.  Then, in lower left of the viewport, the dropdown Add Cylinder!Vertices is where you can change the number of vertices on the curve that comprises the cylinder before the creation of the cylinder is finalized.
But once the cylinder (or other curved object) is added, where is it possible to come back later and change its number of vertices?

The simple answer is: you  can't change the parameters on a primitive object after you've created it and did anything (on any object, no matter if it's the newly created or a different one) like moving, rotating, scaling or going into Edit Mode etc. For more on this subject check this link: https://blender.stackexchange.com/questions/7850/how-to-edit-parameters-for-an-object-after-it-is-created

It's a great answer.  Exactly what I was looking for.  Thank you.

Having trouble figuring out where a "simple single vertex mesh" (suggested in one of the answers in the link) is being started from on Blender. In Add all I see are 3D meshes on the menu. Thanks again for any help with this.

Usually people in tutorials I've seen add a plane, go into Edit Mode, select all vertices and hit M to merge them at center... that's how they get a single vertex mesh.


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Remove/turn off default shader image in refracting object?
2.92 version.  New file.  Object in viewport.
Material Properties!Surface!Roughness = 0
Material Properties!Surface!Transmission = 1
Material Properties!Settings!Screen Space Refraction: ticked
Render Properties!Screen Space Reflections: ticked
Render Properties!Screen Space Reflections!Refraction: ticked
Object appears in Eevee Material Preview with viewport's dark void background with a Blender-default garden picture file that fills the object, and in 6 DOF the garden imagery fills all of it.
Now I drop a sky dome over it, and then orbit:

Where the sky dome appears behind the refracting object, the Blender-default garden file imagery disappears,...but then reappears, resolving into some kind of cube of its own in the refraction.  (The coral colored box is a separate entity.)
The garden file imagery is here, in a shader/texture provided as a default by Blender:

How can that garden image be turned off inside the refracting object (at the very least when the sky dome appears in the background behind the refracting object)?


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Apply vertex paint to a vertex
Through the user interface, you paint a vertex by hitting V in 3D View, and clicking on a vertex.

How can this be achieved in Python?

Why did you ask then answer your own question in the same minute?

@David, I think this page or this page should answer your question.

If you have more than 15 reputation and already know the answer, click the checkbox that says "Answer your own question" at the bottom of the Ask Question page. Type in your answer, then submit both question and answer together.

Thanks for your response. I learned something new. i had view the stack exchange as a place to get and give answers; but now I see it is also a platform for sharing what you already know. This quote states it best "To be crystal clear, it is not merely OK to ask and answer your own question, it is explicitly encouraged."

This function should do the trick:
import bpy

def color_vertex(obj, vert, color):
    """Paints a single vertex where vert is the index of the vertex
    and color is a tuple with the RGB values."""

    mesh = obj.data
    scn = bpy.context.scene

    #check if our mesh already has Vertex Colors, and if not add some... (first we need to make sure it's the active object)
    scn.objects.active = obj
    obj.select = True
    if mesh.vertex_colors:
        vcol_layer = mesh.vertex_colors.active
    else:
        vcol_layer = mesh.vertex_colors.new()

    for poly in mesh.polygons:
        for loop_index in poly.loop_indices:
            loop_vert_index = mesh.loops[loop_index].vertex_index
            if vert == loop_vert_index:
                vcol_layer.data[loop_index].color = color

#example usage
color = (1.0, 0.0, 1.0)  # pink
color_vertex(bpy.context.scene.objects['Cube'], 1, color)

note, the method used to do polygon vertex looping was a bit strange, Ive updated the answer to use a more efficient method.


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Problem lighting inside of a skydome
I'm a Blender noob but made it this far.  I successfully textured a round sky onto a dome that's cupped over the center of the plane grid,  I started from the default start screen (the one with the cube primitive model, and some sort of frustum hanging at an angle overhead, and some sort of light (?) with a corona of double dotted lines circumscribing it at the top of a stick line).  I'm that new.  I deleted the cube.  Everything else remains.
Okay, here's what it looks like:  Imagine a dark, very thin thin-walled black plastic dome, with the black pigment infused into the material such that it's almost opaque but not dense enough; if I'm inside and I look up at an angle and turn to the direction of that light source outside of it, the dome surface gradients and increasingly brightens in between me inside and that light source.  From inside that's where I can see the sky I just pasted onto it pretty clearly.  If I pivot away from that it's going to gradient down pretty sharply to darkness.
But if I try and brighten everything up all around inside by repositioning the light so that it is contained within the dome rather than outside of it, then everything turns jet black inside and I can't see anything.  Another one of those Blender moments.
My question is, how do I brighten the inside of my skydome so that I can see the sky as sunny and clearly as the examples on the web, no matter which direction I turn my perspective on the grid inside?  It's just a stock UV Sphere primitive halved, with a sky slapped on it using the texture tool.  No other tonal values added.
Thanks for any help.

You might also want to explore environment textures, and Blender skies.


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Can OpenGL Render handle (semi)transparency of an object?

Update:  Success with the translucent object under the emitting skydome!
Settings:
I want to make an object glassine, mostly transparent.  Maybe add some partially reflective coating on the top.  Is the OpenGL Render able to do this?
I'd love to try it myself first in order to find out, but every attempt I've made to (a) make something any-alpha at all ends in failure when rendering in OpenGL, and (b) whenever I try to render using anything else, like Cycles, I get no output at all, or the skybox texture isn't rendered at all.  And still no translucency.
Can someone show me how to take a cube (inside of the skydome I've already got), and make it half transparent?  And render okay?  Seems simple, but nothing's simple in Blender.
Thanks for any help.

have you tried enabling glsl in the viewport shading property, and then use the opengl viewport rendering icon-button? (textured or material mode)

Thank you for your reply.  Whenever I have GLSL enabled, my sky inside the dome disappears, goes white back there.

But I also don't know where to find an OpenGL rendering icon-button.  I only know of menu Render!OpenGL Render Image.

I added an answer below to show a possible setup, can't say anything about your "dome"... no details about it?

Okay, that works for transparency, now I've got that.  Awesome!.  Thank you!  (But darn, my sky is still missing with it switched to GLSL though.  Still can't get that to show.  It's either sky with an opaque object in front of it, or white background with transparency in the object.  One or the other.)

I meant: put some visual detail in your question (edit using the link just below it), describing how it's done, its materials. If you wish to share a test file, use this servic http://blend-exchange.giantcowfilms.com/ (free, permanent) and paste the provided link in the question text.

Okay, I succeeded a few hours later.  Thank you again for all your help.  It ended up that the emitting skydome can coexist with a semi-transparent object underneath it.  (GLSL never worked with the configuration, but Multitexture ended up doing it for both the skydome and the transluscent cube simultaneously.)  I'll post the settings I stumbled upon, but there are so many that it will take some time.

(Will work on the partial reflectivity next.)

You got me seeing that the Object parameters have a Transparency setting in addition to the one in Texture parameters.

Her is whay I tried, but I don't know about your dome...


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Zoom--why does it stop so short of the primitive here?

Start a new model
Shift D
Esc
Tools!Vector X:  -30
Manually pan the new faraway duplicate cube into the center of the screen
Manually zoom into that.  Zooming stops far short of it, is prevented from further nearing it

I guess you zoom with your mouse wheel?
This behavior is because the zoom you're using is based on a focus point, which is set on the first object. There are two ways to get around:

set your focus point to your other object with Numpad .
use a "dolly zoom", a zoom which moves your view and its focus point as the same time, with CtrlShiftMiddle mouse button drag

Thanks.  Your second suggestion works for me on this ThinkPad with a desk mouse attached.  (I have a question about the Numpad .--how is that done on a laptop keyboard?)

Check this : https://docs.blender.org/manual/en/latest/preferences/input.html#emulate-numpad


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How do render passes work?
I got a lot of related questions about render passes in Cycles lingering for a while now and apparently I can't figure it out myself.
When it comes to render passes, this manual page with the image below is all the official reference I have found on this topic. This image surely helps, but it is heavily outdated by now. Missing passes:

Shadow, AO - How do they affect the final image?
Subsurface Direct/Indirect/Color - I thing it will behave like the other pass types, but where did this information go previously?
Volumetric - Volumetric information just doesn't show up as a render pass at all, but is still contained in the final image. Why is it missing?

Passes are categorized into lightning passes and data passes. To my understanding lightning passes are somehow encoded in the final image where data passes are only additional information for compositing. Additionally, image passes are noisy by nature and get less noisy with increased amount of samples, where data passes are not affected by samples at all except that they get anti-aliased with increasing samples amount. Am I correct? (related to this question)
Perhaps my biggest question in terms of understanding: How do these passes get generated? AFAIK, Cycles shoots one ray per pixel and sample from the camera where it bounces off from geometry until it hits a light source or gets killed by the Light paths settings. This results in one ray-traced color value per pixel and sample and the colors of every sample get more or less averaged together. Having one color per pixel calculated, where do the pass data come from?

"Cycles shoots one ray per pixel and sample from the camera where it
  bounces off from geometry until it hits a light source or gets killed
  by the Light paths settings"

This is what happens in principle. In practice there are all kinds of tricks and optimizations that make path-tracing much faster than the naive implementation described by you. For example shadow rays are shot from the surfaces in the direction of light sources, and a trick assures that the image converges towards the same image as without shadow rays, but much faster. These shadow rays allow us to collect the "direct" and "indirect" lighting information separately. They are always collected separately, the passes just expose this internal information to you. This shadow rays/direct sampling trick is called "next event estimation" in the CG literature, if you want to learn more about it.

Shadow, AO - How do they affect the final image?

They don't. The information in the shadow pass is already contained in the other passes, and AO is just some kind of fake global illumination, which is not necessary, as path tracing provides physically based GI.
About your other questions: I guess the answer is also in the Cycles implementation details. Note that (according to the Cycles roadmap) in the future Cycles will have AOVs (Arbitrary Output Variables) instead of hardcoded passes.

To add on about SSS/volumes - the reason they're not in the manual graphic is because that graphic predates the existence of the SSS and volume shaders. The SSS trio of passes does indeed work just like the diffuse, glossy, and transmission. It didn't go anywhere before, the pass is as old as the SSS shader itself. I'm not sure why there isn't a volume direct/indirect/color pass set, it seems there should be. Currently volume data only appears in the combined pass.

Is there a place where I can get some more detailed information about how Cycles works?

@piegames The answer depends on how much you know (3d math, C++) and how deep you want to understand. Maybe start here: https://www.scratchapixel.com/lessons/3d-basic-rendering/global-illumination-path-tracing


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Blender VSE proxies show the bad video
I'm editing my first film project in Blender VSE. I had big problems with replay due to my phone's camera using a strange video codec, but this answer fixed it. I've set the proxy option for all strips and generated them and since I care about replay speed and not about preview quality, the proxies are at 25% size 30% Jpeg compression.
The problem is: Blender really likes one of my strips. It's always the same and I don't know why Blender chose exactly that one, but very often during replay the editor shows that strip instead of the actual one. This may happen during a whole strip or just for a few frames scattered around the strip and is really annoying. It usually goes away by refreshing the proxy or turning off proxies for some while, but not always.
Does anyone know why this is happening and how to work around it? I sadly can't upload any examples.
EDIT:
I just found that in the BL_proxy folder there was not only one subfolder per strip, but one more called proxy_misc having the subsubfolder named 25 in it. That one contains all frames of the problematic strip I see all the time in single jpg pictures. I am pretty sure that it is the cause of my problem, but why is it there and what does it actually do? Are there any documentations on what files Blender generates for creating the proxies?

Not sure if I'm completely understanding the problem. You put a very low quality proxy and you are viewing it in the preview window and some of the frames of your strips are now not what they should be...but pressing refresh sometimes fixes it?
The solution to that would be to put a timecode. Specifically Record run. You apply that in your proxy settings. It numbers your frames so you don't get the wrong thing showing in the preview window and you don't get displaced frames showing up in the middle of edits when you render.
Also make sure the thing called channel:0 right under your preview window output is set to 0 or 32, as if its set to anythign else it could be hiding a strip if its on a higher different channel and u wont see it in the preview window

Under the "Proxy/Timecode" for the problematic video, change Storage from "Per Strip" to "Project", then rebuild proxy and timecode. Worked for me.
Edit: it stopped working again. i have the same problem


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Selection tool only selecting some of the mesh
I am not a noob, by any means.  I have been doing this for 8 years, reviewing tutorials and Q&A's religiously since I began and I have never encountered this myself, nor has anyone I've seen ever had this issue, I don't even know if it's an issue with Blender.  I have a very large and expensive sculpt that I have to finish for a client of his dragon character.
For whatever reason, I can select the whole mesh toggling the "a" key, but can not select it normally using any of the selection tools.  It will only select a sparse few vertices outside of the spikes I recently added to his back, but the spikes select normally.  It will not even let me select them manually, and I am in vertex selection mode.  All of the vertices are visible and none of them have been hidden by any means, they are all part of one object.  None of them are overlapping and there are no doubles.  I am at a loss for what to do.  Where can I upload the .Blend?  It's very large.
Just to note two recent events:  Blender was running particularly slow and I watched a tutorial which recommended adding Blender to my NVidia control panel, which I did.  The second is that I ran into a glitch when I was using the Boolean modifier to add the spikes.  Some of them disappeared altogether when I did, but the ones that didn't are selecting normally and the vertices are responding to the selection tools as expected.  The mesh I added them to is what's giving me problems.

EDIT:  I have uninstalled and reinstalled Blender with no change and this is not effecting other meshes that I have experimented with.
EDIT:  I've already tried exporting out the model and hiding parts of it.  Like I said, I'm at a complete loss.

I can see Boolean modifiers still in stack, looks like they are the ones used to add spikes? "Some of them disappeared altogether when I did, but the ones that didn't are selecting normally" means that Boolean couldn't solve some of overlapping / too dense / else comething geometry and those meshes disappeared. This can lead to unexpected behaviour of the rest of the mesh. Either way, with 9 mln polygons Blender can start lagging especially with modifiers. I'd undo Boolean and sculpt the spikes.

I already undid the boolans and it continued, this is a previous save that I tried reverting back to to see when the issue began.  It has nothing to do with the spikes, because I can select them.  I need to know how to fix the mesh so that I can select the rest of it normally.


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What do I do if my render is just black?
here's the link I've got a template from the internet and have been trying to render it.  However when I do so, it takes seconds but it's just a 10 second black clip.  Others that have used similar templates say it should take about an hour to render.
What should I do to try to fix this issue?
(I am new to using Blender so any help is appreciated!)

Also: When I render an image of it, there is color and I can see everything just fine.  It's just when I render the animation it's blank.

If you upload a blend file, then helping you out would be much easier, as we do not know what the problem is (apart from a black render).

How do I go about doing that?

Have you tried rendering out each frame, then using the sequencer to render an animation?

I'm so new at this... I have no clue what it is that you mean- I apologize.

Sorry my internet is being slow. You could add a link to the blend file that you are using.

When I go to edit, what should I click on to add such a thing? I see hyperlink, block code, and code sample.  Which is correct?

Here is a tutorial from Blender Guru on how to render through the sequencer. https://www.youtube.com/watch?v=dd5RT8rEPqU

Upload the blend to an outside source, such as google doc or something, and add in a hyperlink in the above question.

cegaton- It says that my file size is too large to upload to that site

The link you posted requires the original uploader to allow access to the drive to download. So everyone don't have a file to help you out still ...

There is not a single light source in the file you have downloaded. Just
some animation and a few meshes. All you have to do is to add some
light source and it should render fine.
Hope that helps.


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Cycles Textures and the Displace Modifier
I've been working on a procedural texture with the intention of using it in the Displace Modifier, but I've been doing it in a Cycles Shader tree, (simply using an Emission shader to display it).
In the end, I want access to the physically displaced mesh for 3D printing, so Cycles displacement at render-time won't do.. Do I have to reconstruct the relevant Cycles nodes as a Blender Texture? Or can I bake the Cycles renderer's displacement into the mesh?
At the risk of asking two questions, what will happen to the Displace Modifier when the Blender Internal Renderer goes? Will Blender's internal texture system go, too?

It won't be needed to reconstruct the tree if you bake the node tree result on the object and add texture to Displacement modifier - but it won't be procedural any more.


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Dupliframes not rendered in Cycles?
As became apparent after my attempt to  answer to a recent BSE Question..
It seems that Dupliframes are not rendered in Cycles Preview or Final? (They are rendered by Blender Internal)
This is true of two recent builds of 2.79. Windows 10, Nvidia 840m
Is this just a missing setting, expected behaviour, or a bug?
If it is  a bug, is bug reporting still accepted for Blender 2.79, or has everything moved on to 2.8?

Ok, got the answer.. it was a setting.
By accident, in two files from different users, Duplication was set to 'Frames' not only on the Dupli object, but also on its parent curve. I guess it must be an easy slip to make.
I would delete the question, but I've referred to it from elsewhere, so I'll leave it for a bit before deleting it, and the comments which reference it.


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Can you use vertex weights for modeling?
Often, while modeling, I would like more control over graduated transformation of vertices than Proportional Editing makes available. (In particular, it would be nice to be able to have an influence gradient centered on the transformation pivot, changing with distance from it, but affecting only selected vertices.) Some  other applications, in effect, make vertex weights available to the edit system, allowing you to transform vertices proportionately to their weight while editing.
Am I missing something obvious? Is there a route to this in Blender?
One solution to the specific problem I mentioned above is to hide all vertices you don't want to change while using Proportional Edit. This has the obvious disadvantage that you can't see what you're doing - even if you make an instance of the object, with no parts hidden, you only get to see your changes when kicking back into Object Mode (when a bmesh is written back to a mesh??)
To me, it seems odd that the selection of influenced vertices is made by visibility, not by weight.

Maybe use Shape Keys with vertex groups set as mask through Blend option?
As a bonus it is a non destructive workflow.

Won't work for very complex transforms, but for most linear motion should suffice

+1 for the :) .. :) !  .. that's a thought, though  .. I'll see if I can make it practical in some of the situations I've been dealing with.


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Bsurfaces - can't set 'cross' or 'follow'
I'm having trouble using Bsurfaces (GPL, 1.5.1, shipped with Blender)
Sequence of events:

Create mesh object to contain surface
Create series of Bezier splines to be lofted, in a single curve object (The error is also occurring with Grease Pencil strokes attached to the mesh object)
Select curve, then mesh.
Put mesh into Edit Mode.
In the only available Bsurfaces panel, hit 'Add Surface'
The surface is created. So far, so good.
Another panel becomes available: 'Bsurfaces add surface'.
Any attempt to change the 'Cross' or 'Follow' fields in the new panel results in the following error:
Traceback (most recent call last):
File "C:\Program Files\Blender Foundation\Blender\2.79\scripts\addons\mesh_bsurfaces.py", line 3085, in execute bpy.data.objects[self.main_object.name].select = True
ReferenceError: StructRNA of type Object has been removed

This happens with whatever settings I try, (including 'Keep Strokes') in two builds of 2.79.
I've tried repairing the Blender installation, in case I've got the wrong script.. (where would I find one known to be good?)

I've just noticed this is essentially a duplicate of this post, but it does have a little more detail . I'll take it down and edit the previous post if that's the right thing to do

Definitely seems like a bug to me. there's a tracker for bugs in official addons, I'd suggest reporting there.

Ok, thanks. I was kind of asking in the hope that others might succeed/fail in replicating this problem, in case it's not a bug,  preparatory to making a proper report on the add-ons tracker. Is there a forum good for that? Go ahead and close, or I'll delete?

I can reproduce it here on 2.79 and Bsurfaces 1.5.1. No need to delete if you don't want to, this can serve as a pointer to the tracker for anyone else searching. (for some reason developer.blender.org doesn't show up in search results easily, at least for me..)

@gandalf3 As well as your link, it looks as if the 'Report Bug' button in User Prefs > Addons takes you to the right place. I'll make a report.


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Blender 2.83: A shipped add-on is not appearing in the Face context menu
I was recently made aware of the shipped Straight Skeleton Inset add-on  by this answer and this answer on BSE.
I could use this a lot, but in my setup, (2.83 stable), script version 1.1 in .. /scripts/addons .., it's not appearing in any menu.
I can access the operator via F3, but this doesn't allow me to make a shortcut of Quick Menu entry.
The add-on script includes:
def register():
    bpy.utils.register_class(MESH_OT_InsetStraightSkeleton)
    bpy.types.VIEW3D_MT_edit_mesh_faces.append(menu)

Should this work? Any clue what else might be going wrong?

No issue using Blender 2.83.4: https://i.sstatic.net/x0QZM.png (call you've posted is correct) and I can add it to the quick favs as well.

@brockmann Thanks, that helps my hunt, must be an external conflict of some kind, I guess.. I'll run Blender otherwise clean, and see if it works on its own

Any messages in the console?

@brockmann nope, executes normally from F3, just invisible to menu. Can't get to it right now, will try again p.m.


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What are the correct texture coordinates for a lamp projecting an image?
I have studied the answers to @Duarte's question here, and can't get any of the driverless answers to work, either in recent 2.79, or 2.8.
This was after trying my own set-up with a 0-sized point/spot lamp, whose local coordinates are shown.

Using these nodes to shade the lamp..

The Incoming vector should be from the lamp to the lit point which fired the ray. Its X and Y should be the projection of the world onto a sphere around the lamp. To correct the spherical distortion,the vector is  divided by [its own Z / some K], to find the X and Y of the incoming ray in the plane Z = K in whatever space we've chosen.
This works in World space. I had hoped that by using the Vector Transform node, we would evaluate 'Incoming' in the lamp's space, so when we rotated the lamp, the projected texture would rotate with the lamp around the world.. but it doesn't work:

when the lamp is  rotated, the projected texture sticks to the world.
Have the fixes mentioned in the previous answers been 'unfixed'.. or am I missing something obvious? Can anyone make those answers work, or come up with another way to make a rotatable projector from a lamp, without using drivers, now?

I might have misunderstood something, but the setup using the Normal works for me, the texture rotates with the lamp. (https://i.sstatic.net/dINvL.jpg)

@rjg Ahhh.. thank you! (Dooohhh) You haven't misunderstood anything.  It's even dictated for that in the manual. I'd love to know what's wrong with my math, though. I've used 'Normal' or 'Incoming' from the Geometry node. In my slightly wonky mind, for a lamp, which is notionally a sphere, those should all be the same, if converted from World to Object space.That seems to be so, for a mesh-cube. Maybe there's something different about lamps? Trying again in the (GMT) morning..


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Map an image file to a UV dome post-version 2.8
Version 2.92.
Created a UV sphere and lopped off half, so a hemisphere remains.
At present there are by default two panes in the UV Editing tab screen--UV Editor and 3D Viewport, side by side.
After Edit Mode!UV!Unwrap in the right pane (in the 3D Viewport), the UV Editor (left pane) changes from a square grid and a cursor in the lower left, into a round grid that can accept a round map--where I've thus done so:

Meanwhile the 3D Viewport (right pane) contains the dome perspective, but it's still gray.
I want to map the .png in the left pane onto this dome in the right pane.  But how?
UPDATE:
Here is something in the "Base Color" field for Material Properties:

Hello :). @Aster17 is right, you need to assign the image texture to the object. It's only displayed in the UV editor, not chosen as a color :).

Where in the UV Editor do I perform this action?  I've looked high and low and see nothing about setting a material to image texture anywhere.

You need to do it in the Shader editor (or the Material panel you already have opened). UV editor is only for editing UV maps :)

Hey :). Just follow the link, it's all explained there with images.

I'm trying to translate the link app version into present day version.  I've just posted an update above where Material Properties!"Base Color" has an Image Texture option. It appears to have yielded something.

I have seen the pic you have provided and it is pretty clear that you haven't set the material to Image texture. Please change it to image texture and then try UV mapping it, then it should work.


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some vertices don't follow bone chain with Spline IK
I have made a complex ribbon-like structure (DNA strand), rigged it with bendy bones and made it follow an Archimedic spiral. In one strand, this worked perfectly (1st image), in the other some vertices don't follow their bones (2nd image). Deform is turned on for these bones, the weight paint is right - what else could be the problem?
It is maybe notable that I made and rigged the ribbon by duplicating a ribbon half it's length. Indeed, the same three elements of the ribbon are affected (the last three of the original ribbon).

Please note that in the above image I already adjusted the rotation of the elements to all point inwards.

EDIT: I assigned the vertex groups to the bones by hand so this is likely not the problem, I also tried user9288082's answer, to no avail. So here is the .blend file: https://www.dropbox.com/s/y5nmq0palokfs0u/vertices_dont_follow.blend?dl=0

I found the problem, thanks to this answer. It turns out the vertices in question were also controlled by a bone at the very end of the chain.
What I did:

select the mesh, go into edit mode;
select one vertex inside the problematic part of the mesh and bring up the properties bar by pressing N;
under Vertex Weights, check the names of the bones controlling this vertex, there should be one/several too many;
in Pose Mode, select the bone that should not be on that list;
in Weight Paint mode, choose "Subtract" as mode for the Weight Brush and paint over the red areas that should not be controlled by this bone.

Despite your verification, you may still have vertices with a bad weight. To be absolutely sure about it:
1-select all your points in edit mode
2-Switch to edit mode : select armature + shift mesh switch weight paint                                                                           3- On the weight paint menu click on the option: "face selection masking for painting"(see image joint)
4-On the weight paint menu also click on the "limit selection to visible" option
5-Then paint the vertices remaining on the spot with a weight of 0.
The vertices should follow the bone concerned because your paint also in back vertices.
If this solution does not work. Send your blend file.

Thanks for the answer. Unfortunately, I am having some trouble following your instructions. What do you mean by "select all your points"? Do you mean vertices?

I tried it, it didn't change anything. I uploaded the .blend file, the link is at the end of my original question.


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rotate bone around 3D cursor in pose mode
I would like to pose my armature using the 3D cursor as pivot point. However, the bone rotates around its own center, even when I set its origin to 3D cursor. I also tried parenting this bone to another bone that I put in the rotation center. However, my bone of interest steadfastly rotates only around its own geometrical center.
How do I get it to rotate around the 3D cursor?
Edit: It is actually a chain of B-bones. It works for the bone that is highest up in the hierarchy, but not for the rest of them.

you can't use the 3D cursor as a pivot of any bone in Pose mode. Maybe show some screenshots of what you want to do to find another way around.

I disagree with @moonboots here. It is totally possible to rotate bones around 3D cursor in pose mode. The bone you need to rotate that way must be free of constraints that would prevent it though, like f.ex. being a connected child of another bone.

Yes, sorry, I meant you can move around the 3D cursor in Pose mode, but once you begin to animate it won't rotate around as it won't take it into account anymore.

Yes, all these bones are children of other bones. So I suppose I will have to adjust the location along with the rotation?


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Evenly distribute vertices in bezier curve
In Blender 2.79, evenly distributing vertices using LoopTools only seems to work for meshes, not bezier curves. How would one do it for bezier curves? I have seen this post: How to evenly space vertices along several segments bezier curve but find the first solution too much of a workaround. The second solution does not work for me, because Blender does NOT place new vertices in the exact middle between existing vertices when subdividing a bezier curve (see screenshot)

It shouldn't place vertices unevenly when you subdivide a bezier curve, it should place the new vertices exactly between existing vertices.

Possible duplicate of How to evenly space vertices along several segments bezier curve Check my second answer there

@moonboots Somehow, it doesn't (see edited question). Could I have messed up any settings in Blender? I opened a new file for the screenshot.

@Duarte I have seen that post but find the first answer unsatisfying and the second answer does not work for me (see edited question).

Anne, you're right I've never noticed that, I guess I haven't used bezier curves a lot  ;)

I use curves frequently and that never seen that happened subdividing always places vertex at the center. Try checking if your Bézier curve is set to 2D and that there are no duplicate vertex overlapping. Also see if your handles aren't skewing the results

@DuarteFarrajotaRamos Subdividing bezier segments in Blender places the points evenly in relation to the time parameter when moving along the curve. It does not take spacial distances into account. The fact it worked for you is only a coincidence and rare, it depends on the curve shape and how long the handles are. In general those segments are not even, the arch lengths between points differ.

@Duarte indeed, when I select a vertex including its handles and scale it down to zero (by hitting S, then 0), the new vertex appears in the middle between the existing vertices. I guess this will have to be good enough for now.

@Jaroslav thanks for clearing that up. It explains the "weird" behaviour of vertices. My only experience with vertices coming from static vector illustration software (Inkscape, Illustrator), getting used to Blender's four dimensions can be hard for me.


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lowering faces in a mesh
I'm attempting to lower a face with out causing a edge to be pulled down with it how can this be achieved...
I have tried extruding and moving the face downwards, but when I delete the faces that are left I'm still left with the edges present messing up the mesh...

I wish to avoid the second image

https://blender.stackexchange.com/questions/35043/extruding-inwards-leaves-vertices-alone or https://blender.stackexchange.com/questions/51729/what-is-the-fastest-way-to-do-a-cut-extrude-inward-extrude


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Can Rendering Be Paused And Continued?
Just curious to get an idea of how it works, could I pause a project to shutdown my PC for the night and then continue the next day, as I'm aware it can take a long time to render some projects.
It's different from the question it's been link to for similarities, in the sense that it wouldn't be in the same session, the PC would  be turned of then back on, it's a difference worth considering.

It looks like a duplicate at first, but to a closer inspection, the other question deals with an uninterrupted session, while this one asks about turning off the computer altogether. The answer is the same though: there's no such functionality at the moment.

If you are rendering using Cycles, this method https://blender.stackexchange.com/a/87487/16395, together with using "progressive refine", could help. Of course, instead of two computers at the same moment, that can be applied to the same computer on different days.

Are you render animation or still image?

I think a difference this slight should be ignored. I would consider it a duplicate. It is the same question in essence.

Thank you for your comments, I'd be exploring both animation and still images I just wanted to be sure as I've been recommended Render Farms and just wasn't sure if it was worth it, the other topic didn't quite give me the answer I was looking for, given that im asking about the PC being turned of rather than a part of the same session apologies if it created an issue.

If your PC  and operating system supports 'Hibernate' then you may simply be able to hibernate and then resume the following morning. You would need to try it to ensure it works as expected (I don't know if GPUs reliably hibernate and resume.... I would assume so) - there could be glitches if your particular hardware isn't 100% supported.

It does have a hibernate option, never used it but will give it a test tonight to see how efficient it is, brilliant awnser thank you


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Are triangles bad for a mesh
What impact would this have on say a game asset or something like a tank that's animated ?
Asking as I'm piecing together a project that will be involving my own models.
On occasions I've noticed when Bevelling edges the create Triangles on another face, so I wanted to be certain be accepting it.
Thank you

You can find a plethora of articles all over the place dealing with the subject. Like this one, or that one.
TL;DR:

Use whatever works. Quads are the default. But feel free to use triangles when you need to use them. There’s no hard and fast reason to say that you should never use a triangle. Sometimes it’s just easier!

Thank you, I think its because there's so many different articles its hard to get a reliable and definitive answer, some say triangles are bad others contradict it, thanks for the help bud.

Pro tip: when you can see opposite answers like that, then most of the time it's because they are all valid, but depend on their context.


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Drawing a nurbs curve along a surface
I think I've asked this question once before, but I am not sure if anyone out there has an answer.
My question is, is there away that I could draw a Nurbs Curve right along a surface?
As in the Nurbs Curb would fallow a certain shape.
For example, I am trying to re-create a a wire harness / Brake lines for a car, I have a reference scan of it, but I only have the A surface, the other side wasn't captured by the scanned.

I have tried using the poly tool, but it's too complicated and takes a lot of time.
I appreciate any answers you could share with me
Thank you :)

I would just use Snapping.

set Snapping to Face
grab a curve point while holding Ctrl to temporarily enable the Snap to follow the shape of a target object

You can also take a look at Shrinkwrap modifier, but it can be little tricky for this kind of usage.
https://docs.blender.org/manual/en/latest/modeling/modifiers/deform/shrinkwrap.html

That helped so much :) thank you so so very much


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how to set a custom scale size for an object once shortcut button is pressed?
I am aware that I have already asked this question before I apologize ahead of time.
BUT I am STILL struggling really bad with it. as simple as it looks for some of you its really hard for me. The other similar answers suggested to me didn't help since I am super new at scripting.
here is some information----
I am using Blender 2.79b
I'm writing a code that I will eventually turn into addon at the end.
the code is supposed to have 3 shortcut buttons.
button1- to add a cube
button2- to add a sphere
button3- to add a cylinder

Once each button is pressed, I want the object to have a custom scale or dimension.
For example: Once the Add Cube button is pressed, Cube gets created with these dimension (15, 20, 15)
If you can help please be specifi since I have NOOOO idea what I am doing :p
Here is my code
import bpy

class HelloWorldPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "WIRES  &  PIPES"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'TOOLS'
    bl_category = "NEW"

    def draw(self, context):
        object = context.object
        layout = self.layout

        row = layout.row()
        row.operator("mesh.primitive_cube_add")
        bpy.ops.transform.resize(value=(7.5, 10, 7.5))

        row = layout.row()
        row.operator("mesh.primitive_uv_sphere_add")
        bpy.ops.transform.resize(value=(5, 5, 5))

        row = layout.row()
        row.operator("mesh.primitive_cylinder_add")
        bpy.ops.transform.resize(value=(12, 12, 5))

def register():
    bpy.utils.register_class(HelloWorldPanel)

def unregister():
    bpy.utils.unregister_class(HelloWorldPanel)

if __name__ == "__main__":
    register()

Upgrade to Blender 2.90 and above
bpy.ops.mesh.primitive_cube_add(size=2, calc_uvs=True, enter_editmode=False, align='WORLD', location=(0, 0, 0), rotation=(0, 0, 0), scale=(0, 0, 0))
import bpy

class HelloWorld(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "WIRES  &  PIPES"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = "NEW"

    def draw(self, context):
        object = context.object
        layout = self.layout

        row = layout.row()
        row.operator("mesh.primitive_cube_add").scale=(1, 1, 1)

def register():
    bpy.utils.register_class(HelloWorld)

def unregister():
    bpy.utils.unregister_class(HelloWorld)

if __name__ == "__main__":
    register()

bpy.ops.transform.resize(value=(7.5, 10, 7.5))
works inside an Operator.


text:
Object doesn't get motion blur in several frames

I made a robot animation with IK rig. After rendering, as you can see on image 2 & 4, the robot didn't get motion blur at all but the furniture still get the motion blur. image 1 & 3 works fine. I use "Child Of" constraint to connect furniture to the robot.
Closer look:

Motion blur setting:

Am I missing something?
Blender version: 2.79
Render engine: Cycles

Suggest adding a  screenshot of motion-blur settings.

I just added the motion-blur settings screenshot.


text:
Establish a variable inside a driver expression
I'm quite new to python and drivers. I'm writing a rather complicated scripted expression inside the driver-area and I need to repeatedly use a long number sequence. Would it be possible to first store this number inside a new variable and then refer to that variable instead of the number?

The driver namespace
Can add functions and constants to the driver namespace
import bpy

def func(a, b, c):
    return a * b * c

m = 9.4443299912

bpy.app.driver_namespace["f"] = func
bpy.app.driver_namespace["m"] = m

Run the script above, (copy & paste into text editor hit Run Script button,)  to make the new members available to the driver namespace. To make it autorun when file is loaded, give the text block a py extension and check the Register checkbox on RHS of text editor header

Can now consider m in a driver expression to be a named constant like pi and e.
Use in a driver expression like f(m, m, m) Can be typed directly into a field by preceding with a hash # character.  Once the expression is a driver (purple) on editing expression there is no longer a need for #.

There are a number of functions and properties etc already defined to the namespace, a sample of python console output.
>>> for k, v in bpy.app.driver_namespace.items():
...     k, v
...
('asin', <built-in function asin>)
('asinh', <built-in function asinh>)
('atan', <built-in function atan>)
...
('pi', 3.141592653589793)
('e', 2.718281828459045)
...
('f', <function func at 0x7f8f18d34c80>)
('m', 9.4443299912)
('frame', 1.0)

Where frame is the context.scene.frame_current.
EDIT: would like to see a "sub expression" driver variable type where you could do this for scalars, or using other defined variables.  Fitting everything into the scripted expression can be a PITA.

Thanks, this seems like a good answer. I would like to have just one clarification due to my lack of experience: would you add the first part of your answer directly to the expression-field of the scripted expression, or do I need to establish it in a separate python file?

@Antti edited answer, possibly the easiest solution is to make the file autorun  on load.

If you prefer not to use a separate file, consider (lambda m: m * m * m)(9.4443299912).


text:
No transparency in rendered background, is this a bug?
Suddenly I only get a gray background in my cycles renders, even though film-->transparent has been checked and the format is a PNG with RGBA enabled. The image still contains the alpha information (verified in another software) but why is Blender displaying this gray background?
Here is 20 sec video demonstrating the problem:
https://youtu.be/1FqZaiTiCFU

Did it used to work okay in the same version of blender? And have you installed any new addons/updated any recent drivers, etc?

I downloaded an older version (2.68) just to test it out.. Same thing. Could this be a Linux "feature"? I usually work on a Windows machine but I'm trying to migrate to Linux Mint at the moment.

Hmm okay, are you sure that it's not just Linux's way of displaying transparency? Try saving the Image and opening in an image editor go see. Far out I know but worth a shot :)

I submitted a bug report.. They could not reproduce the behaviour yet, so it seems like it might be a bug.

Most certainly not a linux feature (I use linux). The idea that the operating system controls or cares about the way an alpha channel is represented sounds quite silly to me to be honest.. ;)

It might sound silly but it wasn't so far from the truth since it looks like it was a driver issue -which is kind of related to the operating system.

I filed a bug report and did some testing. Seems like the cause of this problem might have to do with my graphics drivers.