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Texturing objects without having to define lots of materials
I'm modeling a track for Assetto Corsa. One of the specifications is that any renderable object must have a material, and every material must have a texture. Up to now, I've been able to model kerbs, trees and similar objects, assigning them a material that has the main texture of the object. However, now I need to model and texture buildings (this is a city track, so it's a urban environment), and I need to assign a lot of different textures to the objects.
After exporting the model in FBX format, I need to import it in the game's own editor, where each material must be configured. Most of times, the default settings (ambient color, specular, shader...) will be ok, but if I have to change them I have to go and edit material after material.
Following my current approach, I would define a Building_StreetX_BuildingA material with the textures for the first building of the first street, then Building_StreetX_BuildingB, Building_StreetX_BuildingC, Building_StreetX_BuildingD... then Building_StreetY_BuildingA, Building_StreetY_BuildingB... This seems to be overkill, and I'm afraid it'll get out of hand quite quickly.
Maybe I could make a single material for a group of buildings, in which all the textures for several buildings will be collected in a single image file. This reduces the number of materials, but it is still essentially the same thing.
I wonder if there is a way to keep the materials count low, maybe with a "physical material" kind of logic (say one material for plaster walls, one for tiled walls, one for marble, one for roof tiles...), while still being able to assign different textures to different faces of different objects.
Is there another approach instead that I couldn't think of? I know most of the concepts, but I'm a beginner when it comes to actual modeling work.

Have you tried sharing the same material but using the UVs of each object to customize them? (for ex: one "building" material with different facades on a large texture and each building picking the facade with specific UVs )

@Bruno I thought of that. It would mean having a gigantic image file, containing all the facades. Would that be a problem? Is there a size "limit" - rather a size that is not sensible to go beyond? What's the difference between having a (say) 500x50,000 texture image, as opposed to 100 500x500 images?

@Bruno Also, as a rule of thumb, what is a sensible resolution for texturing a facade? One pixel per centimeter? One per millimeter?

having a single large texture allows you to have a single material shared between all your objects. Each object using only the needed portion with their UV. But like you said, practical only if the single texture is not too big... the size/resolution depending on how many variation of buildings you want  and how much detail for each building. Are the buildings far from camera?  Get  real closeups? Best is to get a basic scene and experiment with the level of detail that you want for closeups, near sight and background buildings...

I'm asking because if I go for, say, 500x500 facades, then test and decide I should make them larger... I would need to reposition all the UV mappings. But I guess you're right, I have to try a few of them and set for a size and go with it. I'll have to make them one by one anyway, so I'll also test them one by one.


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Particle Systems breaking mesh
I have created ocean using ocean modifier on 6 different cubes and used particle system (on other plane) for rainfall and trying to get ripple effect of rain on ocean water. But when the particles are falling on the ocean, they are breaking my oceans mesh apart (as per screen shot)
When I remove the particle system, it does not break the ocean mesh and works perfectly.  Can you guys help me how to connect the different oceans together so that when particle systems (object) fall on ocean it shouldn't break.

Unfortunately you didn’t show us any settings so providing your blend files would help us figuring out your mistake

If I understand it correctly you use particle systems for a ripple effect, i.e. deformation of the ocean mesh. So deformation will change the mesh, the position of vertices. When those meshes are not connected, they will deform independent from each other and so it will show the gaps between them. To avoid that I guess it would be best if the meshes were joined...

source: Stack Exchange

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

sort: votes


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Rendered Shadow is not sharp
I am texturing leaves on planes and while rendering , it is generating blurry  shadows of the leave object. The same problem occurs with the other objects also.

Any recommended render settings for a sharper shadow?

What do you mean by correct shadow? Without even knowing light setup I could tell you that this one is correct. For some settings.

What is the souce of lighting?if you are using sun, try set the size to zero..as i saw your final render was bit soft (size might be larger than 0)..hope this helps.

Your light source is too big. I can't see what you are using, but if you are looking for unrealistic hard shadows (usually caused by artificial lighting), you need to get a smaller light source. If you are using an area lamp, get the size of it down and turn the strength up. You could also use a point lamp instead. A plane using an emission shader? Make it bigger. If you are looking for natural lighting, this is pretty accurate. Some more rendering samples will reveal the true shape of the shadow.

Moreover, my object was away from the floor also.. Thanks it solved my problem..

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Object not visible properly in compositing
I have solid object cube and i added image in compositor and made the nodes like the following image, but my object is still blur.
I want my object to be visible clearly inside. Please check where i am doing some mistakes.

Could you be more specific? I can't see any blur there, did you mean opacity? Cube should be on top of the image without blending?

You seem to have rendered the cube without an alpha map. You have to use the alpha map in the Alpha Over node as mixing factor.

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Blender Documentation
I am a beginner in Blender 3D, but I can already appreciate the power of this app.
I downloaded this book --> http://upload.wikimedia.org/wikipedia/commons/c/c1/BlenderDocumentation.pdf
However, I am encountering a lot of problems because my version 2.72b and most of what I am reading refers to UI which dates back to older versions.
Can someone help me identify a beginners book (in pdf format) that is updated for the version 2.70+.

I don't think there's one; at least an official one

2.70+ is still very new, so most of the stuff is in online tutorials, not books/pdfs.

Blenders UI has changed with version 2.5 you should ignore older tutorials, for the first steps check http://gryllus.net/Blender/PDFTutorials/AllPDFTutorials.html this question should be closed since we decided to have only one resource question here: http://blender.stackexchange.com/questions/15355/resources-for-blender recommendations for further resources are always welcome.


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Guidance on how to set a plane to look like the sea during a storm
I am a complete Blender beginner and I am trying to follow this beginner's course as suggested by this forum:
http://www.cdschools.org/cms/lib04/PA09000075/Centricity/Domain/81/BlenderBasics_4thEdition2011.pdf
However, I am stuck cause I cannot get the right texture for the water DESPITE doing everything exactly like the instructor says.
In the link below you're see a screenshot of my 2 monitors displaying:
Left Monitor: My Blender 3d with 2 windows, left most showing the rendered texture for the water
Right Monitor: The instructor's PDF file showing how the water should display.
Link is here--> http://snag.gy/eFMIi.jpg
Can someone help me out with this please?

Turn off colour in the influence panel. Only apply this to the normal map

Hi, I tried that but the result is the same  - could it be because I use the blender renders (not the cycles one?): http://snag.gy/n3tea.jpg

Hmmm it could be something to do with the physics tab properties


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Mesh Array Modifier with Fit Curve modifier strings objects through center, not origin
I am using Array modified and Fit Curve modifier to place multiple meshes on a bezier curve.  Unfortunately, blender is passing the curve through the centers of the generated objects, and I need the objects to be placed so that the curve passes through the origin, not center.
Is there a way to do this?
thanks in advance.

What do you mean by center? The geometric center of an object? If so, does it not correspond to the object's origin?

Try using a Follow Path constraint

By "center" I mean the approximate visual center of the object.  I have no idea what point blender is using, but put an array of cubes on a spline and you will see. The spline goes through the middle, regardless of the origin.

"Follow Path Constraint" seems to be for animation. Does it also work for modifiers?

No, follow path works for individual objects. However you can make the origin of the objects go to the center of mass in an object by pressing Ctrl+Shift+Alt+C and selecting Origin to Geometry

That's good to know...but I need to do it the other way...adjust the center of mass to the origin.  I don't think that is going to happen.

OK, I was just being stupid...I'm answering the question in case someone else looks at this issue.
I had set the origin of the bezier to the endpoint of one of the handles...I thought it was on the actual endpoint of the curve.
As a result, even though the origins were lined up and scaled & rotated the same, the modifier was placing the objects with an offset.  It LOOKED like it was going right through the center of the mass of the created objects, but this was just a coincidence.
So...if you have this problem, check your origins again!  Make sure the endpoint of the spline is placed exactly where you want it and its origin is on the endpoint, not the handle.
thanks for the replies.


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Animating for interchangeable model parts?
I've been trying to figure this out for a while and haven't been sure on what to search in order to find an answer to it.
I am creating a game in Unity whereby the player will be able to equip individual armour pieces (like chest/legs/gloves/boots/weapon/offhand etc).
I know how to animate an entire model with an armature, but I'm unsure of how to animate model parts in separate model files.
Upon inspection of a few other games, I have seen a few with a separated 'armature' file that I assume handles all the animating for all model files, but I'm not sure whether this is the direction I need to go, and I'm not even sure how I'd go about doing that.
In addition to this, some model parts may have unique bones related to them (for example: a shirt with a tie, and another shirt without a tie), would I put these bones on a single armature even though other connected models parts would not be using these bones?
I assume there's a simple way of doing this, as it'd be very inefficient to do a hundred or so animations for each individual armour set (with having to apply transformations, weighting and vertex groups to all of them).
Could someone please point me in the right direction?

I would just have the character have all of the bones it needs in the original armature, just not all would be in use.

In blender you can parent an object to a bone (eg. parent a glove to the hand bone), you also have a child constraint that you can keyframe the influence of the parenting. Not sure if that can transfer to unity, you may even be able to change parenting settings by script within unity.

My first instinct is to use a single armature, and have different meshes with an armature modifier pointing to the same armature.  In simple cases you could instead parent the mesh to one bone in the armature.  In more complicated cases you can use the armature modifier and vertex groups with weights to have the mesh modified by the appropriate subset of bones.
How exactly that translates to Unity, I am not sure.


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Blender Python Property change event - Execute function?
i am wondering if it is possible, to execute a function if the user changes a custom property of an object?
For example, i create a custom property "MyInt" for every selectable object in the scene. This property defines the rotation of the object from the center point. If the user now changes the property i want the object to spin around the center. For that reason i would like to know if it is possible to react to a "property-change" event and move the object accordingly to the property value?
My code:
import bpy
from bpy.props import *

bpy.types.Object.MyInt = FloatProperty(
    name="Rotation in °",
    min = -180.0, max= 180.0,
    default = 0)

class Panel(bpy.types.Panel):
    bl_label = "Object Rotation"
    bl_space_type = "PROPERTIES"
    bl_region_type = "WINDOW"
    bl_context = "render"

    def draw(self,context):
        layout = self.layout
        col = layout.column()
        col.prop(context.active_object, "MyInt")
        return

def register():
    bpy.utils.register_module(__name__)
def unregister():
    bpy.utils.unregister_module(__name__)
if __name__ == '__main__':
    register()

Yes you are right, that solved the problem. Thank you very much!


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L and R poles are flipped using Rigify
When I generated the rig I noticed that the L and R poles (set to the proper feet by default) are flipped. This obviously causes quite a few issues. I used the metarig in 2.91 and only removed the facial controls.

Make sure your metarig's legs are set up correctly.
The only bend allowed in an IK chain is the one to indicate in which way it should bend. If you do it wrong, Blender will orient your IK wrong.
Also check your bones' orient.
As you can see below, I just shifted the metarig knees on the side and it generated the same way as yours.

Thank you. I'll double check them. The process that I did was from a tutorial that mentioned to do a recalculate roll on the character which is where I now believe where the issue came from.

After doing some experimenting it appears that was exactly the issue. Even though it appeared that the bone axis were correct; adjusting the bone roll (shift + N) seemed to mess with the knees. Thanks for your help on this.

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How to keep my particles from getting messed up once converted?
If this were sphere shapes for something like marbles I wouldn't mind, but I'm trying to do some grass. It all looks good while not converted.

But then I convert it and ...

How to avoid this?
Thanks guys,
DPC

Can you define 'converted'? What are you converting it to?

I was missing making them all single objs before joining them. Got to make a note of that...

In the Modifiers stack, on the tab corresponding to the Particle sys, there is only one big horizontal button called "convert". Once you use it it'll create one independent mesh per particle. Which you can of course manipulate in many different ways to suit your needs. Without affecting your still controlled particles.


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How to use the textured material from a multi-mesh object onto a single mesh obj?

The above bush is made of many initially individual images on planes, one per plane (leafs). Then joined into one mesh. This mesh uses 2 materials.
 But now I need to replace all these planes with one mesh (which I already made with the Re-mesh modifier, and lots of cleaning).
 At first I thought I could bake all those planes into one texture to then just apply it to the other single mesh. But after baking I can see it is only using one of the many planes, hence the result is one big leaf in my baked image
 Any ideas?
Feel free to inspect the blend
Thanks guys,
DPC

Quick mapping (sloppy) of your image on single sphere mesh on the left to simulate your starting point. Middle image is placement of the two participants of the bake. Then baked onto another final mesh on the right side.  The 3 images are different stages of the baking process.
The created texture has black background which becomes transparent via color ramp and transparent shader.  I nested the hemisphere askew to increase readability.  All the hemisphere shapes below are a single mesh.  Your are seeing objects below with transparency so you may need more time to get the orientation of the object.  I may correct this.

Created texture with black on left.  Mapped texture with black.  Objects baked in alignment.  Below.

Two alternatives.

Consider Baking in Cycles Render or Blender Render.  You will use a new texture to record the color reflection of one source mesh to the other target mesh.
Your finished original bushy mesh can be illuminated or set to emission material.  We assume your shapes are roughly hemispheres. Hemisphere is sphere cut in half.  The target mesh is hemisphere with reflective surface.  Original mesh in placed over the reflective target.  Bake target mesh.  See video references for detailed instruction on baking in cycles render or blender render.

Consider creating a regular rectangular tile of leaves texture, which is expected to be modest work. Leaves in this texture can all be same size. New mesh is cylinder.  UV Map cylinder to leaves texture.  Leaves appear all same size as in the soup can model.  Use proportional editing to reshape cylinder in to hemisphere.  In this scenario your original bushy collection of meshes is discarded completely... rather I mean ... placed gently in the experience bin.

Abbreviated Picture Notes
Blender Cycles Texture Baking Setup
In the following the red object is your texture object with emission material.
Red emission object is next to green reflective object follows

Bake Result is the New texture follows

Texture placed back on green inner object and rendered follows
Original Red object has been set to No Render.


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Why is my Normal map not working?
Only Bump seems to be showing the concavity I'm looking for (not with the same map, I use an inverted version of the B&W spec map you see in the nodes setup).
But the moment I switch to Normal (the nodes setup below), not only the concavity won't show, but the glossiness is gone!.
This Bump is not too shabby, but Normal is supposed to be better. Plus not knowing why is not working is killing me!
Should you want to inspect a simple blend file  I made, by all means!
Thanks in advance guys!

JDL

Image texture nodes with normal maps loaded should be set up as Non-Color Data.

Also in addition to Mr Zak's comment the normal map is not normalized, it is too strong, which results in black glossy shader (so no glossiness).

Try connecting the Normal Map to the Diffuse node

@Jerryno  How can the normal map not be normalized?  I'm pretty sure the output of a normal map node is always normalized.

@PGmath in RGB image each channel can have value of 1.0. That can add up to a normal vector length of > 1 (1.73). The base of vectors can be also left hand or right hand and I've seen some pretty nasty normal maps with shuffled or mirrored channels. I doubt the normal map node is all_powerful and always gives a nice output.

As the others have said change your normal map image from "Color" to "Non-Color Data". Also your normal map should be hooked up to the diffuse through the normal dot AND the normal dot on the glossy shader.

It should actually be plugged into both the diffuse and glossy shaders.


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Rig not moving mesh correctly
I'm trying to port The Riddler from Arkham City to Garry's Mod, and to do so, I copied a male armature from Half Life 2 and parented The Riddler model to it with automatic weights.
I then went into Edit Mode and spent a long time assigning vertices to the bones (not many, as I was just testing) to make the rig more accurate, but when I went into Pose Mode with parts of the armature selected, they did not move correctly with the mesh.
I then parented a collision mesh to the armature as well (as this was needed), and that worked fine.
I'm very confused as to why The Riddler does NOT move in time, as I remember trying Automatic Weights again, with the same results.
Here is the .blend file I'm having trouble with.
Possibly an easy fix?

its ripped so i wouldnt be suprised if it doesnt work the first time

Ripped? You mean from the game or the vertices are ripped/not joined? BTW, have you actually looked at the model? It'd help.

Ripped , as in from the game .. Ripped also as in , Every single quad is a tri now , So it extremly difficult to rig . One way to fix it is by turning all the tris into quads by dissolving ... That would take a very long time though . Also , I THINK you might be able to rig even though you have tris but im not entirly sure . And i did take a look at the model

Well, did you try to position the rig in Pose Mode? You'll see what I mean about it not moving right-although it IS rigged.

yes , i did and im not sure why its happening , Maybe try to rig it without scaling the bone , and the weights will be applied alot better

I already tried re-rigging it- 3 times actually. Without scaling the bone? I kinda feel that wouldn't work. Strange there aren't any solid answers yet.

You need to seperate the loose parts of the mesh (P in edit mode). You also need to connect the head and tail of the bones, so the bone heat can be calculated properly.

Blender uses solid bones with a head an tail separated by a body.  What you have here is many very small bones placed at the joint locations.  I am not very familiar with Maya but I think this is done in a Maya style where joints are king.  Basically when you are rotating a "joint" in your blend you are spinning a very small bone around a central axis.  You need the head of the shin bone for instance to be in the knee and the tail of the shin bone to be in the ankle.  Then when you select the bone in pose mode put the 3d cursor on its origin and make rotation pivot the 3d cursor.  When you rotate now you will see a stick bone rotating at the knee (like a real shin bone) and the mesh will move like you expect.  You may need to re-weight it but with doing one bone fast it seemed like it would be ok if I got everything straightened out.


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How to save animation as a video format
I am basically trying to make an intro for my youtube channel. I am sort of familiar with the program because I was playing around with it for a long time, getting the basics of it. With the help of youtube videos I am basically done with my project. I put my name in it and everything. I just need to know how to save the animation onto my desktop as a file that I could open and would be in a video format.

You need to render your animation. It's recommended to render to an image sequence first, then render the image sequence to a video file. Specify an output directory and file type (e.g. png) and press Ctrl F12 to start rendering. Once done you can press Ctrl F11 to preview your animation (warning, loads the image sequence in ram, so you can potentially use up all of your ram if your animation is long). Then put the image sequence in the VSE, set the output type to the video format of your choice and render again.

Set the Output to "AVI JPEG" in the render settings.

Also , to set the place where it is saved , Click next to "/tmp/" , That folder image. Then select where to save. After doing all these steps you can then render and it will appear where you saved it.
UPDATE:
One of the big changes in 2.79 is that they finally separated containers and codecs.
The encoding options from previous versions are still there, but now they have organized differently
If you select FFMpeg video, there will be a new tab for Encoding options.

There you can select the container and the codec for the output file.
Container is the file format for the file, (Mov, Avi, Ogg, MP4, to name a few) sometimes is referred as a "wrapper".
Codec (short for Compression-Decompression) Is how the image is compressed. The picture quality, file size and processing power needed to view the file are largely determined by the kind of codec used and the settings used for it.

What if you've already rendered the animation and accidentally saved it in the wrong format. Can you re-save a previously rendered animation in a different format without re-rendering?

To answer my own question, it looks like you can follow the answer here http://blender.stackexchange.com/questions/15142/how-to-render-an-animation-as-video-in-blender but instead just import the 'mistake' video file instead of the image sequence into the Video Editor, then go back to Default view, set the correct output settings and click 'Animation' to re-export the video in the new format.

you can add sounds in the video sequence editor.


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Rendering artifacts in blender internal
I'm experimenting with drawing textures onto the model. I'm trying to render what I've got so far, but my renders come out with these strange black or white rectangles all the way down the blade edge. Anyone know a fix for this?

Some of your issues (the handle area) are from textures

It all came down to a loss of precision in the depth buffer, let me explain.
You have your camera's Start Clipping set to .001, that is tiny.
If you turn on the display limits of the camera you will start to see the problem.

The camera is in the red box, and your sword is in the blue box, over 60 units away.
Now with the start clip set to 0.001 (the default is 0.1) there is a lot of wasted calculations, leading to a loss in precision.
The blender manual has a note about such behavior with a large clipping range.
This Quote from an article on MSDN explains it well.

The near plane and far plane are the final pieces required to calculate the projection matrix. The more closely together the planes are, the more precise the values in the depth buffer.
The depth buffer can be 16-bit, 24-bit, or 32-bit, with values between 0 and 1. Generally, depth buffers are fixed point, with the values close to the near plane grouped more closely together than the values close to the far plane. The degree of precision available to the depth buffer is determined by the ratio of the near plane to the far plane. Using the tightest possible near/far plane could allow use of a 16-bit depth buffer. A 16-bit depth buffer could reduce the use of memory while increasing processing speed.

So a simple fix, is to set the camera's start clipping to a bigger number, even 0.1 works, but as your scene is currently set up you could go as high as 60.

Changing the camera settings will fix the problem, however you still have a huge sword.
If you look at the dimensions (in the properties panel N) of your sword it is 31 meters tall!
Just scale down the sword with S, until it is about a meter. Then reposition the camera.
The other option is to scale down your entire scene, then change the strength of your lamps.
This has the same effect as changing the clipping on the camera, because there is now less space blender has to calculate.
So really this was a story of way too big, and way too small. Pay attention to your numbers, and even use real world units.

You are a beautiful person. Thank you for this :)

Is it ok to use real world units if my object is 3 million km wide?  :D  I'm having a lot of problems with what are probably these clip start/end issues.


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Is it possible to stack two or more materials with transparency for textures?
I have a model I want the "base" material to be Blue, and I want to apply a material with an image texture to some selected faces only. The image I want to apply has transparency, and I'd like that transparency to show through to the other (base/blue) material. I've had no luck with mixing a transparency shader using the alpha channel as the factor. I'm doubting whether its possible this way. If it's not possible, how should I go about doing this instead?
I wanted to use the material node, but that doesn't seem to be in blender any more.
Thanks in advance :)

My mask image:
White mask with transparency

Does this answer your question? Add a transparent image on top of a material

The problem you are having here is that the separate material is acting as you want it to. It is making the faces that use the second material transparent and thereby looking through those faces. Those faces are not associated with the base/blue and therefore are not blue. If you want the transparent areas to be blue then I'd recommend one of the following:

Make these selected faces a new object that sit on top of the face (duplicate, separate, move slightly). That way you have your entire head with only Skin, and the new object with only Eyes white mask.
Instead of Transparent BSDF in your Mix Shader you make it the same material setup as your Skin.

In the material tab, go to Settings and change the Blend Mode from Opaque to Alpha Blend or other related Aplha options

That makes the texture actually transparent, as opposed to blue like I'm looking for. You end up seeing inside his skull around those edges. The other blend mode settings have similar unwanted effects.


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How can I unwrap an object with minimum distortion in the UVs?

And by "good" I mean with minimum distortion, keeping the original shapes for the most part, etc
So far, after doing the seams, I've been doing with the best choice I can find from the various alternatives the UV/Image Editor can offer, depending on the mesh (Unwrap, Smart UV Project, Project from V, etc). Then I refine it so more with things like "Minimize stretch, and Average Islands scale". And manually straighten vertices with the old trick Scale + perpendicular coordinate direction + 0 + enter. But of course this method can take a long time, not to mention it can be tedious too.
I found a couple of seemingly great scripts at BlenderAddonList, like UV Squares, and UV Tool. But maybe due to not being updated they are not working today with 2.75a :(  Either way, it occurred to me I may not be looking in the right place after all.
I thought there was a tool in Blender called "Relax UVs" in the UV/Image Editor. But I don't see it, could it be it was in 3D Studio Max? It used to do a great job, like Minimize stretch, but better.
Any pointers, ideas, suggestions, etc will be super appreciated :)
Thanks in advance guys
JDL

Please place an example screen capture of your blender model so others can give you some specific concrete advice.

You should really take another look at UV Squares. It's working fine for me in 2.78c.

If you really don't want to have any distortion at all, that means that nearly none of the faces of the object may remain connected as a UV image. To achieve that all faces keep their original shape and size you can simple unwrap as Lightmap pack. However, all of the faces will now be separated making it hard to see which face belongs where. Those are the off trades of having no distortion.

Incase your doing some painting on it, and want the real size of your faces.
select whole object, mark seams (all face get seams) and unwrap.
There is another way for strange shapes that is a bit more configurable
for better resulting maps.
In mesh edit menu, there is an option to select 'sharp' edges.
First deselect everything, then go fo 'sarp edges' select.
You can give a angle degree (using mouse slider), to select more or less sharp edges. Then do a mark seams, select all and perform uv unwrap.

The other answers are good, but I think they're using the word "distortion" differently than you are.  (Their use is the more common use, btw.)  You want a nice straight UV map, right?  And your mesh is something like an edited torus?
In the case of the specific UV map you're providing, it's doable.  No, you don't need an addon to unwrap that without weird curvy UVs.
1) Select all UV coords ('a' once or twice in UV editor)
2) Reset UV (U->Reset)
3) Re-select a face to make it active
4) Follow active quads from length average (u->follow active quads, confirm defaults)
5) Pack your UV into your texture space (ctrl P in UV editor)
On the UV map you've provided, seamed as it is, you will have a perfect, square UV map, with only the two seams you have in your image.
Another good technique for this, for other kinds of meshes, is pinning and re-unwrapping.  Getting clean UV maps can be very different depending on your exact mesh.
Blender does have a UV relax, but it's called something different.  It's "minimize stretch" and it's available from the UV menu of the UV editor.


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What's the fastest way to change textures for 100 objects?
I had to convert all my PNGs to JPGs, reason why now I need to switch to those new texture files.
Batch converting the image files was easy and fast. But how to do the next step in Blender now?
Thanks in advance guys
DPC

You can replace the filepaths using python and then reloading the images:
import bpy
for img in bpy.data.images:
    img.filepath = img.filepath.replace('.jpg', '.png')
    img.reload()

Great!
JuhaW from BlenderArtists suggested a similar solution, also with "import bpy":
import bpy
for i in bpy.data.images:
i.filepath = i.filepath.replace('.png', '.jpg')
What do you think?

I did try your code, but I must be doing something wrong:
Screenshot of error after running script:
http://blenderartists.org/forum/attachment.php?attachmentid=430177&stc=1
And this is a screenshot of the console:
http://blenderartists.org/forum/attachment.php?attachmentid=430178&stc=1

identation error means that you've missed the spaces at the beginning of the line. Python is very picky about those things, try copying the script exactly into your text editor, then it should work.


text:
Where to find Blender's Prefs/Settings files in Ubuntu 14.04?
First off, I did notice there's a similar thread. However, I needed to add that my files have a date for last year (?!). Really odd, I'd think, because I've been using Blender just couple days ago. Isn't the date of those files supposed to be updated every time I use Blender?
Btw, using the graphical Files Manager app, I found 3 files here:
 Home/.config/blender/2.77/config/
1. bookmarks.txt, 2. recent-files.txt, 3. userpref.blend
I need to install Blender in another pc soon. But it would be great to save the time needed to setting up Blender.
Thanks guys,
JDL

Thanks. Even if it dates back to last year?


text:
Some images are painted on. These changes will be lost. Continue?
I get this message when attempting to pack all textures.
My actual question is: How to easily locate those "unsaved" textures?
I did this before with a copy of this file and there were no problems. The difference this time around is that I packed some textures individually. Then I went to the File menu and chose External Data/Pack all into .blend.
Thanks guys,
DPC

Thanks for replying cegaton :)
I am quite aware of what you say, BUT "...My actual question is: How to easily locate those "unsaved" textures?"

If you have all these images saved as files intially (via F3) and there's unsaved paint since then, you can use UV/Image Editor > Image > Save All Images.

Also in Outliner there's property for whether image is unsaved - open Datablocks, Blendfile Data > Images > imagename > Dirty. If it's checked then image has unsaved changes.


text:
Possible Bug - My material color won't change
This is in Material Preview shading mode. As you can see the colors chosen in the nodes do not correspond the one showing in the viewport for the sphere. Same thing for the Object Properties/Viewport Display. If I apply a 2 nodes material then it’s ok. But there is something with these set of nodes that won’t pass the color chosen in the nodes to the object. It did belong to a more complex set of nodes. This one is a simplified iteration (for troubleshooting).

This is in Solid shading mode:

Can someone pls inspect the .blend file?
badmaterial.blend (833.8 KB)
Thanks guys!

You must have deleted something from the original node network.
Your color ramp is not driven by any coordinate based texture so you will only get a solid color (assuming the same color at every point on the sphere). Since your ramp is a gradient of grey and you are mixing it 50% with black, you end up with a middle grey solid diffuse color! No surprise there!
To see the effect of the ramp, simply add a texture that's based on some sort of coordinates for example a Musgrave Texture, a Noise Texture or a Voronoi Texture would do. So would an Image Texture...

Thank you Bruno. I also noticed that if I slide the left Gradient tick to the right, THEN I can see that tick color in the object (which is what I needed). I really don't need a gradient, I just wanted a means to have a solid color here, but I didn't find any other way. Thanks a bunch again!

Well if you want a solid color, just remove Mix, ColorRamp and Musgrave Texture nodes and use the Diffuse BSDF color input (click on it to select your color!)


text:
Can elements of a collection be moved up or down?

Let’s say I want the NM.Top.Soil layer to be above Far.Mountain. I don’t see the way

No, it's alphabetical.

This functionality is very much needed.

The order is alphabetical, but you can use it as an advantage.
I frequently use codes at the beginning of my objects names to determine their order, like:

"AAA Cube"
"AAB Sphere"
"AAF Empty"

This way those object will always be at the top of their collection

This will do the job while that functionality is added. Great idea! Thanks a bunch!

Same here but I use numbers; my brain can parse their sort order more quickly.


text:
How to animate Light's Power/Strength in 2.80?
I know this was asked before, 4 years ago. But it's not working in 2.80.

You can do it the same way you animate most other quantities in blender. Go to a frame, set it to the brightness you want, then right click on the Energy slider and click Insert Keyframe from the menu. Go to another frame, change the value, and insert a keyframe again. Then it will automatically animate the brightness between those two points.
Below is an image of inserting a keyframe.

This is actually the exact same process as in the other question you posted, and it works for me in 2.8. If this doesn't work, maybe say more specifically how that method didn't work for you.


text:
How to have 2 Mats w/alpha each and a base Mat on the same object?
I need to have the Base.Color material on all the cube faces. With the setup I have I cannot. I have to choose between the materials with Alpha, or the Base.Color material.
I did try adding a 2nd UV map but apparently only one can be renderable at the time.
Thanks in advance guys.

Have you assigned two different materials to two different faces? https://blender.stackexchange.com/questions/516/add-different-materials-to-different-parts-of-a-mesh

As the screenshot shows: 3 materials have been assigned to one cube (Choc.Donut, Blue.Donut, and Base.Color). The tricky part in my case is that I need 2 materials on the same set of polygons: the base material, and a texture with alpha on top of it.

So if your intention is to create decals, there are other posts on the matter: https://blender.stackexchange.com/questions/15207/setup-a-decal-material-in-cycles

Excellent! Yes, that's just what I needed! Thanks a bunch Denis :)

Use decals to place textures over the main texture. See other answers: Setup a decal material in cycles


text:
How to catch light without the object it is hitting on for compositing? (2.80)
I want to render a neon sign along with its emitting light on the wall behind. Then composite it to a real video with Camera Match.
I suppose I'd need to render the light with transparency (somehow). But how exactly?

Possible duplicate of How can I render a spotlight hitting a transparent wall?

https://blender.stackexchange.com/questions/19765/cycles-shadeless-shadow-catcher-material-for-rendering-onto-footage and https://blender.stackexchange.com/questions/518/how-to-make-a-model-cast-shadows-onto-the-world-texture-background/ and https://blender.stackexchange.com/questions/14898/render-shadow-on-transparent-background-with-blender-render/

I'm glad you brought this to my attention Duarte. Any chance you could delete the other one?

I can't delete them myself, directly, but I can flag it for moderation; but since you authored the post you should be able to delete it yourself

I think the best lead so far is this one: "what you need is the emission pass, youll need to place the plane on the position of your wall and activate the emmision pass from the cycles render settings, you can the extract the pass from the render layer node and use it to composite the emmission onto your footage. you should be able to extract the shadow pass too so you shouldnt need to have a seperate plane for both shadows and emmission" from Chris (cgjam.net)


text:
How to put a video or Img Seq over a video?
I am trying to put either a MP4 video, or an Image Seq over a video. But unfortunately the video shows with a black background although I did change the Render/Film/Alpha setting from Sky to Transparent. And the Image Seq shows in bright pink.
Compositing Noodle

Image Seq Noodle

What could I be missing?

Pink color means that Image file couldn't be loaded

The VSE makes this much easier. Do you need to use the Compositor?


text:
How to share/copy Grease P. materials from one Collection item to another? (2.80)
How to share/copy Grease P. materials from one Collection item to another? (2.80).
There must be a way!

I found that copying a layer from one object to another also allows you to import all the materials present on that layer. Maybe it can help.


text:
How to control the line thickness of a drawn object with Grease P. (2.80)
How to control the line thickness of a drawn object with Grease P. (2.80)
I scaled down a drawing, but now the line is too thin.
Thanks

In Object Mode select the GPencil object, then go into Edit Mode
Select the curves/vertices you want to modify
Use Alt+S (or alternatively from the context menu through Right Mouse → Shrink/Fatten)

The stroke thickness can be controlled in the adjustment section for the grease pencil layer.


text:
Where to find custom created Grease P. Brushes? (2.80)

Where to find custom created Grease P. Brushes? (2.80)
So, I’m pretty sure I created a couple custom brushes, but I don’t see how to go to them now :(
Thanks guys

Thank you for trying Yash, but I can tell you were only guessing. Why? Because both guesses are wrong. And because I found where it really is.

This is how it is really done:

It's easy to overlook because the icons representing the brushes look the same, and have almost the same name. Although the complete name of the last brush is "Draw Pencil.001" but it would only show in the upper left corner of the image above, where it says "Draw Pencil" now.

I think it has two.
You may Click on 2 or Draw P... or the logo to the left of Draw p....
Then you may find your grease pencils there.


text:
modeling cube into cylinder
I am new to blender and currently trying to learn modeling techniques. I would like to change a square into cylinder. From what I've read the easiest way would be to use the array modifier and warp it around a bezier circle and then extrude that object. But I was wondering if there are any tutorials on how to do this using only transforms and only a few subdivides....To be specific, I'm trying to make a pillar object from a cube

possible duplicate of How to create Quarter Cylinder

@LeonCheung not so much duplicate as related and pertinent, good to reference here.

I took the liberty to simplify the provided answers.

Leon Cheung-method:

Bevel Ctrl+B edges and use Clamp Overlap C while beveling.
Example:

stacker-method:

Enable LoopTools Addon that comes with Blender.
Then, use: W > LoopTools > Circle - Even though sometimes you need to manually adjust some angles.
Example:

Method 1
Starting with a scaled default cube you could add a loop cuts along all axis' Ctrl-R like so:

Then select the middle loop cut ans scale it S

Open the specials menu W and select LoopTools/Circle Note that the Looptools must be enabled in the User Preferences / Addon

Result with a Subsurf Modifier added:

Method 2
(Suggested by Leon Cheung)
Select the edges of the scaled cube like so:

Press Ctrl-B for Bevel adjust the radius by moving the mouse and add cuts by turning the mouse wheel.

Result after adding and scaling a loop cut around z-axis and sub-surfing:

Could also do scale to circle, I believe the key is shift+alt+S, but I am not entirely sure.

@user1894167 lol, I misread your question and thought I've read pillow but you were asking for pillar.

@stacker, i just didnt subsurf and added more bevel sections to your method to get a pillar

Here's how I would go to create a cylinder:
Here's my cube;

I add a Subdivision Surface modifier. (change the number of divisions based on how smooth you want your cylinder to look.

Here is what the cube now looks like.

Hit Tab to go into edit mode and select the top and bottom faces (edge select)

Hit N to open the properties window. look for the Mean Crease option under Transform. Set it all the way up (1.00).

Here's what it'll look like.

Just Tab out of edit made and you've got a wonderful cylinder. (apply the subdivision surface if needed.)

Thanks. That looks like a better way of doing it just using transforms and subdiv like i wanted.

@user1894167 I am sorry but this method does not produce a cylinder. Subsurfaced surfaces are not round - the subsurfaced cube is not a sphere nor this is a cylinder. The bevel or verts-to-circle are both accurate methods.

@user1894167 I agree with Jerryno, the final result is not strictly a cylinder. Whatever, it would be okay assuming you needn't a perfect one.


text:
Is it possible to get Vray like renders using Cycles?
I deal with architectural visualization. I have used Vray before and I have gotten excellent results. I am struggling to get the same or about the same results with cycles. So my question is...is it possible to get the same or about the same results with cycles as it is with vray?
Thank you

Largely yes. not exactly the same, but when you're skilled enough for it to make a difference, you'll know what render engine you need. For now cycles will do just fine, some truly incredible renders have been made with cycles.

I've seen some good results such as http://cgcookie.com/blender/2014/07/08/architectural-contest-results/ http://cgcookie.com/blender/cgc-courses/interior-3d-architectural-visualization/ http://www.thearchitectureacademy.com

related: http://blender.stackexchange.com/questions/14246/how-is-cycles-different-from-v-ray/14270#14270

This type of result is technically possible, but will depend on your expertise in Cycles. The render engine will not be the limitation (it may be harder, though). I am voting to close this as primarily opinion based.

The two are based on basically the same principals.  The main difference is the way they define materials.  The cycles nodes system can be harder to learn for most people, but it can be much more flexible (and in my mind often simpler) once you get the hang of it.  So, as the others have said, you can get basically the same results, it's just a different way of going about it.

I have the same situation. In Cycles I'm playing a lot with compositor and post-production (dark-table) which can help, but V-ray still is much better in terms of realism and professional results, even without post production. Have you find a way to improve Cycles?


text:
Pose automatically mirrors
Whenever i try to pose my model, it automatically mirrors the pose on the x-axis. Fx whenever i try to lift the right leg, the left leg does the same. How do I get rid of that? I'm using Blender v2.72.
Thankyou!

Are you in Pose Mode? With an armature in edit mode there is an option for x-axis mirror. Bone constraints or drivers should be the only thing to cause a mirror effect while in pose mode.

Pls upload and give link to your blend file to for inspection, you can use http://www.pasteall.org/blend/

I'm guessing that you have a mirror modifier.  If you apply the mirror modifier and then reparent with automatic weights, that will fix the problem.  I do not know if there is a way to keep the mirror modifier and prevent this problem.


text:
Part of model disappears when zooming out
When I go into camera lock mode and zoom out on my model. The distant parts grey out and disappear. Why is that?
Kind regards,
Maarten


text:
UV Distortion on Helicopter
I'm currently modelling a low polygonal model for a game and just finished unwrapping and organizing my uv map. I'm not very knowledgeable about uv mapping, so I was wondering if the distortion in these screen shots is acceptable enough to move on to texturing.
As you can see, I mirrored the chopper down the middle to conserve space, but it seems that there's some distortion around the center areas. Is it okay to leave it as is or is there something I should do to fix this?

That looks nicely done, Go ahead and texture it. When you're finished, show us the results in chat

Basically the only way to tell if it's unwrapped sufficiently is to give it a texture and see how you like it!

Try to make sure that the polygons are planer before unwrapping, this will reduce stretching.  You can also fix this after and then adjust the UV Coordinates in the UV Image Editor.  Some stretching is unavoidable for curved surfaces.

as long as no complex textures need to be there (and they shouldn't if  you want to be able to see from the cockpit) it should be perfectly acceptable to have a material that is basically uniform.

Disclaimer; I've been called sloppy on this before, but never had bad results.

The UVs are ok. Depends how much time you are willing to spend on them.

You would like the checker pattern to be mostly squares
The squares should be same size everywhere
The UV seams should be on least visible places

You can improve on the second point and also reconsider if there is better placement for the seam on the cabin. If there will be text on the heli the mirrored UVs will not work on the hull and so the cabin could have 1 UV island then.

I believe the cabin seam is because he is using a mirror modifier.  I don't know for sure but it is a pretty good guess.


text:
wrong image texture keeps being applied

I am texturing using two different images.  The first one for the cats head worked fine but when I come to use a new image for the cat's body, blender keeps using the first image. See below.  On the left the eyes from the first image appear on the side of the body. can anyone suggest a fix for this?

You need to give the object two different materials with the different textures.  The textured view mode doesn't display the material texturing, just the active texture (whichever texture is shown in the UV/image editor).

@NoviceInDisguise  It's totally possible, just give the two areas different materials.  I don't see anything wrong with using different texture files.

What? Using multiple separate image textures in a single material is done all the time! You just need to be sure to define the right UV maps for the right images on your material. See http://blender.stackexchange.com/q/2176/599

authors: បង ហូខ បង ហូខ


text:
Can I get an IK constraint w/ stretch to only scale bones on their Y axes?
I have a short IK chain with an IK constraint with stretch enabled.  The bones in the chain each have their Inverse Kinematics Stretch set to 0.001.  Here's a simple demo setup...

Moving the Control bone around within reach of the IK chain seems to work fine.  E.g.

But when I cause the stretch to take effect by moving the target out of reach of the IK chain, the chain stretches and scales in all 3 dimensions causing the mesh to expand.  Note the size of the mesh and IK chain bones relative to the target as compared with the other images.

Is there some way to only have this stretch along the Y axes of the bones?  I.e. I want the bones and mesh to elongate but not swell.  I have tried various other settings, including locking X and Z scaling on the bones.
You can grab a .blend file of the sample setup at http://readyposition.com/Blender/IKStretchExperiment.blend
Help appreciated.

IK stretch bones do stretch in all 3 axes and can't behave like you want.
The solution and common method is to

duplicate all the bones in the chain (except the control) and un-parent them from each other
for each bone_copy set Copy Location and Copy Rotation constraints targeting the original bone
for each bone_copy set Stretch To constraint targeting the next bone in the chain. This constraint should have Volume set to XZ to maintain reality or to None if you only want to stretch in Y axis
bind the mesh to the copied bones

Thanks.  I came up with that solution as well.  I was just hoping to simplify.  And this does it.


text:
How can we animate a ball rolling over a path?
So I have an complex smooth surface.  I created a high resolution path curve and used a Shrink Wrap modifier to make it fit on my surface where I want it.  I apply the shrink wrap.
I can easily make an object move along this path now with a Follow Path constraint.  Great.
But...I would like to animate a ball rolling along this path.  I can't find a constraint or other tool in Blender that allows for this.  If I knew how Python interacts with Blender better (I'm just learning) I would write something using quaternions (I've done this in an iOS physics engine I did a few years back).
Or is there some trick with rigid body simulation to make my ball roll along the constrained path?
What's an animator to do?

It might be possible to do something with a curve guide force field and the rigid body simulator. I'll give this a try later.

Seems curve guides don't affect rigid bodies? Odd, as there is an influence slider.. Perhaps a bug.

You can make the ball roll with a Driver, first - this is what you should already have setuped, make sure the ball's Follow Path constraint option Follow Curve is set:

Add single driver to the X axis rotation field (RMB on field > Add Single Driver R)

Setup the driver like this (scripted type, no variables), also make sure Auto Run Python Scripts in User_Preferences > File is enabled:

Lets add a driver variable for the curve evaluation time, call the variable "eval_time", in the Prop field put the curve and Path is eval_time:

Now its time for the driver expression. You will need to know the ball's diameter and the curve's length.

diameter you get from ball's dimensions in properties panel N:

curve's length you get from running this script with curve selected:
 import bpy
 import bmesh
 orig = bpy.context.active_object.name
 bpy.ops.object.duplicate_move()
 bpy.ops.object.transform_apply(location=True, rotation=True, scale=True)
 bpy.ops.object.convert(target='MESH', keep_original=False)
 bm = bmesh.new()
 bm.from_mesh(bpy.context.active_object.data)
 edge_length = 0
 for edge in bm.edges:
     edge_length += edge.calc_length()
 bpy.context.window_manager.clipboard = str(round(edge_length,3))
 bpy.ops.object.delete()
 bpy.context.scene.objects.active = bpy.context.scene.objects[orig]
 bpy.context.object.select = True

It will calculate the length and store it in the clipboard, you can then paste it with Ctrl+V.

The driver expression is: -2 * curve_length / diameter * ( eval_time / eval_max ):

Let's break the expression down:

(eval_time/eval_max) is the only element that changes and it goes from 0 to 1 as the ball moves along the curve

the rest equates to a number, that says how much has the ball turn to rotate along the whole path
If the ball turns 1 complete rotation (360°), it will travel pi*diameter units.
So to cover the path it needs curve_length / pi*diameter of full rotations.
The catch is that driver expects the input in radians, not degrees. So a full rotation of 360° is 2*pi radians.
(2pi) * curve_length / pidiameter, we can simplify and remove pi
The last thing is the minus in front of the expression (-), this is to influence which direction we want the ball to roll. You can use the right hand rule to see what rotation is positive, and what negative (thumb in axis direction, fingers point in positive rotation direction).

Now the ball will roll accordingly to your curve's Evaluation Time:

This is awesome!  Thanks.  Now I have to read up on this stuff so I can do things like this myself.  The more I learn, the less I know. :-)

This video is a good start to drivers.

Pinging Jaroslav towards the question below...

Hi @ThomasKordi, I included info how I got that expression


text:
Can I make a camera use the lens distortion parameters determined by camera tracking?
The camera tracking utilities allow you to specify or estimate lens distortion parameters (k1, k2, and k3).  Is it possible to get the Blender camera to adopt this specific distortion?  I can't find a way to set these directly on the camera.  Nor can I find a way to get the lens distortion in the compositor to take these.
I have a really great track on a very wide angle scene with a very nice distortion.  I can't seem to match the distortion perfectly.
Thanks in advance.


text:
How do I copy video strip properties?
I'm editing a video made with several movie strips. I've changed the properties of one of the strips, like the blend mode, the opacity, the saturation, etc.
I want to copy those properties to the rest of the movie strips, is it possible? Or do I have to modify every strip manually?

You can just do it by

Selecting all strips.
Changing value in the active one.
Do a right click with mouse cursor over changed value.
Choose Copy to Selected item in Pop up menu.

There is an addon called 'Property Chart', you can display a listing of all selected objects properties as well as copy the first property to all others.
This isn't ideal but it at least saves doing it manually.
@user188's answer is better but keeping mine since its still useful at times since you can see all properties at once.


text:
How to render a 30K image with cycles?
I have to render an image of 27000 x 7000 for a 150dpi print. The scene is quite big, but cycles preview and a render in 2700x7000 works as expected.
If I hit render my memory raises up to 20gb, but my cpu usage is at 5%. Why cycles does not using the full cpu power during the render process?
Here are my rendersettings:
Pathtracing
Samples:3000
Tilesize: 64x64
Bounces: Max 12 | Min 3
Diffuse: 4
Glossy: 4
Transmission: 12
Volume: 1

Is there a way to optimize things?

Are you reading the 5% cpu when it is rendering, or just starting, during the Building BVH?

After building bvh, when the image is rendering the task manager says: 5% cpu usage. In the last 20 hours cycles has rendered 269 of 26311 tiles at 4-6%.

Odd.. I tried this too, rendering the default cube at 27000x7000 my cpu stayed around ~50% (waffling around a bit). At 2700x700, my cpu was glued to 100%.

Commandline rendering seems to work (100% cpu usage at the moment).

I had a similar situation and realized the rendering was happening mostly on the GPU, leaving the CPU at limited usage: see here https://blender.stackexchange.com/a/187901/102048

With very large image resolutions Blender can run out of RAM. The operating system will then start using the hard disk for memory which is slow and will cause low CPU usage (swapping).
To reduce memory usage for very high resolution renders:

Enable Save Buffers in the Performance panel so Blender does not keep the full render in memory during render
Render from the command line so no display buffer must be kept in memory
Output to an OpenEXR file so one tile can be written at a time

In my test I still had over half my ram free.. Blender used 1.5GB out of 15.7GB total. CPU usage was at 100% while building BVH and preparing, but dropped to about 20% once rendering started and stayed between 20% and 50% for about a minute, at which point I stopped it. Rendering from the CLI worked fine.

I also have swap disabled.

Displaying a very large image is probably a bottleneck too, which could be avoided by hiding the image editor that is showing the render result. In any case, the command line will have the least memory and CPU overhead.

Makes sense.. Though I still don't see why drawing the huge image would cause less CPU usage.. Wouldn't the CPU still chug along as fast as it can, just put not quite as much effort on path tracing and slightly more effort on (communicating with the GPU?) to draw the image?

Ideally yes, but threads may need to wait writing to the render buffer while the display thread is drawing it.

Also, such problems would be worst when rendering a default cube, on a complex scene and using 64x64 tiles CPU usage will probably be higher.


text:
How to make object transparent on "texture" view mode
I have managed to make an object transparent on solid viewmode, but It is fully opaque when "texture" viewmode is selected.

The reason I need it transparent for textured view is that I'm editing the object to match a picture projected on a plane behind it. Help!

Right now I can work around this issue by hiding and revealing the object  repeatedly really fast and get a similar effect...

If you're rendering in Cycles skip this.  The gif sweeps through a bit fast but to catch it but you don't appear to be selecting "Material" view mode.  Try that and render in OpenGL, see if that gets the results you're after.

You can do it in Material viewport shading, which isn't all that different from Texture.
Set the shading to Material and add a material with the following node setup to your object.

On the Properties Editor make the following changes.

Now change the color of the RGB node to your liking.

If it's imperative that you use Texture shading, the following method should suit your needs just fine (it also works in Material shading):


text:
How to wait for bpy.ops.wm.alembic_import to finish?
Quite a simple question I hope, I've been tearing my hair out with it for over a day now though. I'm trying to write a background python script that will import an alembic and then perform certain actions on it.
I can get the alembic to import by calling bpy.ops.wm.alembic_import with the filepath, however this import appears to occur in a separate thread which means that the code I immediately move on to still sees an empty scene.
Is there a way to make the python script execution wait until the import is finished, or insert a callback that will be called once the import is finished? I've tried the load_post and scene_update_post callbacks with no luck.

bpy.ops.wm.alembic_import operator provides a property called as_background_job which defaults to True. In that case the alembic import will happen asynchronously.
You can override the default behavior by passing a False value, in which case the import happens synchronously (blocking Blender)
bpy.ops.wm.alembic_import(filepath='....abc', as_background_job=False)

I had the same issue,
This is my current solution:
import bpy, time

#get size of total scene:
sceneSize = len(bpy.data.objects)

#do my import:
bpy.ops.wm.alembic_import(filepath="E:/Projects/blender/RenderCam.abc")

#wait for scene size to change:
elapsed = 0.0
maxTime = 10
while(sceneSize==len(bpy.data.objects) and elapsed < maxTime):
    time.sleep(0.2)
    elapsed += 0.2

#do something with imported thing:
bpy.context.scene.camera = bpy.data.objects["RenderCam"]

basically keep checking the size of the scene until it changes - then assume that the import is complete.
I welcome a better solution if anyone knows one.

Turns out this only works for small imports (eg cameras).   if I try to import an abc with lots of stuff it ends to early.....

Maybe read the alembic file for the object count first, then use that as a gauge for when to proceed?

That is not a predictable and reliable way. I have added an answer which overrides the 'as_background_job' alembic_import operator property.


text:
Shearing a group of objects
[][3][![transformed object][3]][3]I have a group of objects and I need to give them all an equal shear  during an animation (like a matrix transformation).I tried using the lattice. It does distorts it(like a shearing) but it does not give an equal shear to all the objects.
The first image is of the object that I wish to transform.
The second image is of the object after it has been transformed but the objects itself seems to have become separate and this is not how a matrix transformation operates mathematically. Please help me to understand what is the lattice deform transformation doing and how to use it such that it is in accordance with matrix transformation.

Could you post some screenshots of what you currently have and what you want to achieve?

Lattice Deformation should do what you want. Is it possible to post the blend-file on https://blend-exchange.giantcowfilms.com/ please?

I realised that if the lattice encloses the objects completely and if the options are changed from bspline to linear, it does the job.


text:
How do I set the location of the 3D axis?
I am new to Blender, so this is probably a common question.
The origin and the 3D axis indicator are in different locations. This affects how modifications applied in edit mode via S and mouse drag.
I found the N panel that lets me enter origin location.  How do I set the location of the 3D axis indicator?
Also, how is there any way to lock the origin so that it does not change with every left mouse click?

You're mixing several terms. Position of the axis indicator (it would help if you show screenshots btw) is called the pivot point; it will be the same as 3d cursor if pivot is 3d cursor. Origin of the object can't be moved neither with left nor right click, it's only Move Origin command or moving geometry in Edit mode. Precise location of the 3d cursor can be set in N panel as well in 3D Cursor rollout.

The 3D-Cursor is one of the unique and very useful features of Blender, albeit sometimes confusing to new Blender users.
The issue you mentioned seems to be because of the pivot center for rotation and scaling set to use the 3D cursor PERIOD key (the before the ? key).
If you press COMMA key the rotation/scaling transformations occur about the Bounding box of the current selection.
The 3D cursor has many uses in Blender.

The 3D cursor is where new objects get added in the scene
The 3D cursor can also be used for setting a temporary pivot axis for an object and then perform rotations and scaling (by pressing PERIOD). To reset the 3D cursor back to world origin, press SHIFT + C

Custom 3D Cursor placement behavior
If you really do not want the 3D cursor to be shifting when LMB is clicked, then you can customize it from the user preferences. This is an advanced customization step and must be followed carefully.

Invoke the User Preferences Window CTRL + ALT + U
Search for Set 3D Cursor
Click the white triangle to expand the key map.
If I want the 3D cursor to be placed when I hold SHIFT and CTRL keys and then press the left mouse button, so I check SHIFT and CTRL.
Try it out in 3D view
If satisfied, save the user preferences.

That's not the origin, it's the 3D cursor. Not wanting to move it, is akin to trying to work with a text editor without moving its cursor.

I am looking at an example where the 3D axis indicator (the 3 arrows showing x,y,z) is different than the origin.  The origin (the dashed circle) is in the center of a cylinder.  The 3D axis is affixed to one of the ends of the cylinder (different for the origin).  I would like to move the axis indicator to the cylinder end.  I see how to move an origin.  How do I set the location of the axis indicator?  Secondly, the origin changes every time I left click.  Is there a way to lock this during edits so that I don't have to reset it all the time?

Every object has an origin (its "position" in the world), The world also has an origin at (0, 0, 0). The red/white dashed circle is not an "origin", it's the 3D cursor. You can configure Blender to use it as pivot point for certain operations -- Blender can use the 3D cursor, object origins, the average point of all selected objects' origins, etc. Please see the 3D cursor and Pivot point manual sections.

Pressing Shift+C will return the cursor to the center of the xyz axis (and re-center the scene visually if there are objects in it).
Pressing Shift+S reveals a drop down menu with many useful options.


text:
Poll method for custom panel
How do I setup the poll method for a panel causing it to only display when 2 objects are selected ?

    @classmethod
    def poll(cls, context):
        return len(context.selected_objects) == 2


text:
(bpy.ops.mesh.transform.resize)how do I call this operator as a modal rather than directly executing it?
I was trying to call this function as a modal through code but unfortunately when I execute bpy.ops.mesh.transform.resize(long list of values here), it applies the function directly and I want this as a modal just like when I press the "S" key triggered through code.

I haven't worked with modal operators yet, but there are some modal script templates shipped with blender that might be a source of seeing how it works.

I know how to make custom modal functions, but how do I access the existing modals like the resize(face,vert,edge), knife tool,etc ?

To adjust the properties used by an operator, which is referred to "redoing" the operator,  you can use the operator panel at the bottom of the toolbar or press F6.

No, this isnt what I'm asking, I'm asking how do I execute the existing modal functions like the resize, scale, knife tool.etc through code.

You can achieve the behavior you desire ( user interaction ) by explicitly passing the execution context (INVOKE_DEFAULT) as the first argument.
bpy.ops.mesh.transform.resize('INVOKE_DEFAULT', ......)

The default execution context is 'EXEC_DEFAULT' and is implicit for all operators. In such a case just the execute() method defined for the operator is called using the default or passed operator properties. But in case an operator defines an invoke/modal method and 'INVOKE_DEFAULT' is the execution context, either an operator properties user interface can be used to execute the operator or can be run modally or both.
Further details can be found at the links below:

bpy.ops calling operators and execution context
bpy.types.Operator


text:
Keep strips height when pressing home
I am still trying to get familiar with Blender's interface, to use it for video editing.
Now, when you press the home button, it shrinks the strips in order to see the whole timeline. I would like to know if there is any way to use this option but keeping the height of the strips that i set.

Don't forget, you can scale the view with Ctrl+MouseMouseButton with individual control over height and with.

Pressing Home key will scale all strips to the current view. You can split your VSE timeline to a second view with all clips, use this to navigate and select strips, then in the larger view press Numpad Period. The preview window will still show the current frame from either timeline.

There is no way to change this behaviour.

View all Sequences Home
  Zooms the display to show all strips.

But there is a similiar command.

View Selected NumpadPeriod
  Zooms in the display to fit only the selected strips.

This will zoom to the selection. An alternative would be to quickly select all then view selected.
A, (A,) NumpadPeriod
This will preserve the height scale.


text:
How to Reopen the 3D Viewport along side the UV Edit Window
I opened the UV edit window and made a uv map. Now I want to open up a second window with my model in the 3D viewport. I want to synchronize the mesh and the uv map. But I can't figure out how to open the 3D viewport.
Thank you for your help,
Sabia

Related - http://blender.stackexchange.com/questions/36239/how-to-open-a-timeline-window and http://blender.stackexchange.com/questions/1223/how-to-close-open-a-view-panel

I have created a hotkey for performing this most frequently needed operation with areas.

RMB click on the edge between two areas
Choose Split Area
Right Click on it again.
Choose Add Shortcut
Press the hotkey you would want to use for splitting areas (I used CTRL+ALT+SHIFT+X)
Then press the hotkey to initiate the split.
Pressing MMB button can change the direction of split.
Click the mouse when satisfied with the proportions of split.

References
Arranging Areas in Blender

Adding a new resizeable area is done by grabbing the diagonal lines ("little ridged thumb grips") that are present at the corners of all areas and moving them to the desired direction, to obtain an "up-down" or a "left-right" split.
Once created, each area can be assigned to a different type of editor.
An area can be removed by "coalescing" a neighboring area onto it. This is done by grabbing the same handle and, while holding the mouse button, moving the pointer to the center of the area that you need to remove.
Here's an animation of what you are trying to achieve

Hope this helps.

I decided to simply shut down with Ctrl+Q. When I came back in, I was able to cleanly do what I wanted rather than trying to exit wherever I had gotten to! So I recommend that to anyone. Save if you need to, Ctrl+Q and come back in! Do not try to find your way out of the labyrinthine paths of Blender. :-D
I read some of the manual's interface info as suggested. Thank you for those suggestions.


text:
Is there a modifier to transform proportionally along a circle? (for tri-lateral symmetry)
What I'm actually trying to achieve is a hack for modeling with trilateral symmetry.  I'm trying to achieve this with the following modifiers:
Starting with a model like:

1 - Mirror Modifier (mirror in X and Y) to give 4 identical quadrants.  This gives me something like:

2 - Boolean Modifer (use a big cube to remove the 2nd quadrant i.e. upper left).  I only allow the cube to draw as wires so I can see through it.  This give me something like:

3 - Some sort of deform modifier (this is the crux of my question) that will close the shape in some reasonable way to achieve trilateral symmetry and allow me to continue modeling only in the original "quadrant".
Simple deform doesn't seem to be the right thing here.
Mathematically there are a few ways to do this, though scaling everything along the circle seems to be most natural and gives me the result I want.  So I could implement any of those transformations in Python as a one off.  But I'd rather hear someone experienced with Blender say that one of the deform modifiers does the trick for me.
Thanks!

You could use a curve modifier, after your current setup, or an array with object offset, using a rotated(360/3 degrees) empty

Maybe this helps: http://blender.stackexchange.com/questions/23659/how-to-use-array-to-create-circular-array-without-spiralling

Brilliant, @Jerryno. I had to tweak it a little to make it right.  It is even more general that I had hoped.  Writing up the answer now.

Thanks to @Jerryno, I have an even more general solution than I was hoping for.  In fact, it addresses any degree of symmetry that I need.  Here are the details.
Here is my base geometry with only a subsurf modifier:

Notice it also shows a Bezier circle that I will be using.
1 - Add an Array modifier with a fixed count of 3.  Notice that Merge is checked.

This gives a result like:

2 - Next we want to use a Curve modifier to bend things around the circle.

This gives something like:

3 - Don't fret about the gap.  In order to close the gap, select the Bezier Circle and type "3/pi" in the X Scale and Y Scale.  Since Blender interprets the Python expression it will show .955 in the cells as in:

Which gives the very satisfying result of:

Interestingly, if you change the Array modifier fixed count to anything, N, and change the scale on the circle to N/pi, you can get higher degrees of symmetry (e.g. w/ N = 5):

How cool is that?!  (Man, I love Blender!)
One more thing might make this even more convenient.  Since we have an odd number (3 in my case) of repeats, it isn't truly symmetrical.  When I edit, it looks like...

If you want this edit to be truly symmetrical (i.e. each edit affects 6 analogous areas in the final geometry), then put a Mirror modifier for the X axis first in the modifier stack and only start with half of the original geometry.  And we get...

So to summarize, the full recipe of modifiers for this N-lateral symmetry is:
1 - Mirror Modifier in X
2 - Array Modifier w/ a fixed count of N
3 - Curve modifier with a Bezier Circle
4 - Make sure the Bezier circle has a radius of N/pi

I had posted another answer to my question that addressed the original situation I was facing.  But since I'm designing an entire series of objects with trilateral symmetry and some with some very different topology, I thought I'd adopt a variation of the solution presented by @cetagon here.
The problem with my other solution is that it maps everything in the original model above the X axis to the outside of the circle and everything below the X axis to the inside the circle.  While this works for my original problem, it leads to a lot of confusion and crazy math to try to get resulting geometry that is close the origin.
So here's the solution I am using now.  This is also generalizable for N-way symmetry, but I'll show the 3-way case here.
With starting geometry that looks like:

1 - Add a Mirror modifier to mirror in X to get (be sure to select Merge and Clipping):

2 - Add an empty at the origin and rotate it around Z by 120 degrees (1/3 of the way around).
3 - Add an Array modifier with relative offset 0, select Object Offset and specify the Empty object.  Be sure to select Merge and First Last as in:

This yields...

I left it in edit mode so that you can see that only the one bit of geometry needs to be edited in order to get the fully symmetrized result.
Editing near the seam opposite the original mirror edge can be a bit wonky at times since it seems impossible to automatically get the clip behavior you get with the mirror modifier.  I'm open to suggestions on that.
Also, do people prefer this approach or the other approach better?  Or can someone think of something even better.  I'd rather just have a more flexible mirror modifier but I'm not that far in understanding the code base yet.  Only approximately 24 hours in a day.

I realized that I could have just unchecked relative offset instead of making it 0.


text:
How to use API to get an object's constrained position?
I'm using Blender 2.8 but this question probably applies to older versions as well.
Scenario:

I have an Empty located at the origin.
I have a Bezier Curve.
The Empty has a Follow Path constraint targeting the Bezier Curve. This
successfully causes the Empty to move along the path.

What I need is a way to access the modified location of the Empty after the constraint is applied. I only seem to be able to get to the original unconstrained location (0, 0, 0). E.g.
>>> D.objects['Empty'].location
Vector((0.0, 0.0, 0.0))

Help is appreciated.

After much digging around I believe for this simple case I can get what I need in D.objects['Empty'].matrix_local. E.g.
>>> D.objects['Empty'].matrix_local
Matrix(((1.0, 0.0, 0.0, -0.7031904458999634),
        (0.0, 1.0, 0.0, 0.0),
        (0.0, 0.0, 1.0, 0.29674994945526123),
        (0.0, 0.0, 0.0, 1.0)))
>>> [D.objects['Empty'].matrix_local[i][3] for i in range(3)]
[-0.7031904458999634, 0.0, 0.29674994945526123]

There is also matrix_world (which is the same in this simple case). But if there is a better way to do this more generally, I hope someone will illuminate us.


text:
Can I copy grease pencil from UV/Image Editor to 3D View?
Perhaps there is another easy workflow for this. Just trying to get relative measurements for something in the UV/Image Editor by drawing a few lines with the grease pencil. Then I want to copy the strokes to the 3D View and then rotate (2D) and scale them as needed as a guide to designing objects.
I know I can load images into the 3D View background or load images into a plane in the 3D view, trace things with grease pencil, convert grease pencil to geometry, etc... But for my workflow it would be much more convenient to be able to quickly transfer grease pencil strokes (as strokes or geometry) between views.  It would be nice if this was generally available between all views.


text:
Can python callbacks be registered on viewport user actions?
Is it possible to have python callbacks invoked when a user does something like select an object, bone, vertex, etc...?
For example, imagine a FK/IK setup where clicking on certain bones trigger the FK/IK switch and other necessary modifications. This isn't precisely what I'm trying to do but it should get the point across.

Try a search on msgbus

Interesting. Looks like it lets you know about changes to datablocks. Not sure object selection qualifies. I tried some experiments to see if I could register interest in bpy.context.selected_objects but couldn't get my callback to be invoked. Maybe I need an example.

Not sure msgbus works with context. The other one to look at is a depsgraph update handler which runs a lot.  or just remembered this one https://blender.stackexchange.com/questions/160909/handle-vertex-property-changes-with-msgbus-subscribe-rna


text:
Where is the surface emission for materials to create a light source from a plane?
Im currently trying to create a light source from a mesh plane, and a tuturiol explains that i need to add a material and then select surface>emission>strenght 10. I can't seem to find a way to edit surface in 2.72b

Cycles:
Method 1:

Set the render engine to cycles
Go into the node editor
Check Use Nodes
Delete the Diffuse Node X

Click images for larger versions

Method 2:

Set the render engine to cycles
Go into the materials panel
Click Use Nodes
Change the Surface to Emission

Internal:

Check that you're using internal
Go into the materials panel
Set the emit value
Check shadeless (to look like cycles)

wow thanks for the quick response..you rock!

@NoviceInDisguise Note that that functionality is part of the Node efficiency tools addon.


text:
animation render playback hidden on OS X
When I "play rendered animation" the playback is hidden under the gui and I have to minimize the entire gui to view it.  It doesn't matter which display option I choose in the render panel.  Single frame renders display correctly in whatever display option is selected.  Macbook Pro retina with Mavericks 10.9.4.  Can't figure this one out!!

Works fine for me on archlinux with openbox, but I imagine this is OS (and maybe even DE) specific. Sounds like blender ought to ensure the window is focused or something..

I can confirm the same behaviour on OS X. But it's probably best to report this as a bug: https://developer.blender.org


text:
Using Blender to investigate the cast of shadows from an object onto a specific point in space
I think that Blender might do what I have in mind, but I am not a Blender and Python guru, so I am looking for directions.
I need to determine if a point in space is obscured by an object, i.e. does it cast the shadow over it (there is one source of light, the sun). This has to be done for:

many different objects of different shapes but of similar size: they are fairly simple with just a few surfaces (e.g. a collection of cubes of slightly different sizes and orientations). Each is stored in one OBJ, so there are many OBJs. The analysis should be done one by one.
a collection of many points that need to be tested, each has different 3D coordinates. For each point it should be determined if a shadow is cast over it or not, so the result is binary.
for a different position of the sun (e.g. 100-200), to mimic the variable position of the sun during the day and throughout the year.

I am interested in two things: how to automate this, and is there a function in Blender that determines if a point is obscured or not.
What I have so far is shown below. For the simplicity of the approach let's assume that all points that need to be tested have the same Z coordinate (i.e. they are planar).
for each OBJ:
    +Load the OBJ
    +Place a plane at the Z value of the points to be tested
    for each position of the sun:
            +Render the image so only the plane with the extent of the shadow is visible
            (option Cast Only, and the camera is orthogonal and has a top view.)
            +Export the image
            +Import the image with an image processing library in Python
            for each point to be tested is a shadow cast over it:
                            +Find the pixel in the image that corresponds to
                            the position of the point
                            if the pixel value at that point is dark:
                                   it is obscured
                            if not:
                                   it is not obscured

Is there a better method for this? Please note that the points might have different Z coordinates, so my method is not optimal (it would require multiple planes).

I would like to point out that the blender python has an API for ray_casting objects so you don't have to manually loop over all the faces of the object your self.
http://www.blender.org/api/blender_python_api_2_63_8/bpy.types.Object.html?highlight=object.ray_cast#bpy.types.Object.ray_cast
import bpy
from mathutils import Vector, Matrix

SunObj = bpy.data.objects['Sun']
sun_mx = SunObj.matrix_world

Surface_Object = bpy.data.objects['Test Points']
surface_mx = Surface_Object.matrix_world
for v in Surface_Object.data.vertices:
    v.select = False

#here some simple test objects
test_names = ['Torus', 'Suzanne', 'Cone']
test_objs = [bpy.data.objects[name] for name in test_names]
test_mxs = [ob.matrix_world for ob in test_objs]

#we get the sun location from the world matrix
sun_location = Vector((sun_mx[0][3], sun_mx[1][3], sun_mx[2][3]))

#Test test points are stored in object data
test_points = [surface_mx * v.co for v in Surface_Object.data.vertices]

hits = 0
for ob, mx in zip(test_objs, test_mxs):

    imx = mx.inverted() #ray_cast happens in local space
    for i, pt in enumerate(test_points):
        loc, no, indx = ob.ray_cast(imx * sun_location, imx * pt)

        #simulate shadow with selection of the test vert
        if indx != -1:
            hits += 1
            Surface_Object.data.vertices[i].select = True

print(hits)

a sample blend
https://www.dropbox.com/s/004eu6aaqxg6zxy/ray_cast_sun.blend?dl=0

You dont need to render any images or setup any planes. This is what you should do:
for each OBJ:
    +Load the OBJ

for each position of sun:
    for each point to be tested:
         +Create a ray starting at point with direction of sun (sun's local Z axis)
         +Test if ray intersects any of OBJs, if yes:
             it is obscured
         if not:
             it is not obscured

sun's local Z axis you get from up_vector=(0,0,1) and sun's world_matrix:
from mathutils import Vector
up = Vector((0,0,1))    # global Z vector
up.rotate(bpy.context.scene.objects['SUN_NAME_HERE'].matrix_world)
# up is now sun's local Z axis - the ray direction

The part Test if line intersects any of OBJs is done by looping over all OBJs triangles and testing mathutils.geometry.intersect_ray_tri() function.
If your object have lots of triangles test the OBJs bounding box first.

Thanks. I didn't expect it to be so simple. I will vote your answer after I get some reputation.

I fixed the api intersect call, it was old 2.49 api. This will work in current blender.

I have started to implement this, and I am stuck at the mathutils function: I have managed to convert each triangle from the OBJ to the Vector type, but I do not know how to do the same for the ray of the sun.

point_loc = mathutils.Vector((x,y,z)) where x,y,z are coords of point to be tested. sun_loc = sun.location where sun is bpy.data.objects['YOUR_SUN_NAME']. Then ray is (sun_loc - point_loc) and ray origin is point_loc

Thanks, but as far as I know when it comes to the sun, the sun.location is irrelevant because the location of a lamp of the type Sun does not affect the rendered result. Only the rotation is important (which I do not know how to use here).

Oh sure, i forgot that your rays are parallel. The direction of sun is its local Z axis. Updated the answer with how to get it.

Jerryno, thank you very much for your prompt answer. I've also up-voted your answer now that I have enough reputation :)

Jerryno, I have finally implemented the algorithm. It works, but not completely as I had it in mind, because the computations go "beyond" the point to be tested. For instance, when a point is above a plane and between the sun and the point there is nothing, the function returns an "obstruction" (i.e. an intersection), since the ray "continues" to the plane. Do you know how to solve this, and to "stop" the ray at the point to be tested without going beyond it? I can compare the height values of the point and the intersection, but I am sure that there is a better solution.

I see, consider 2 vectors point-intersection and ray. If their dot product is greater than 0 they have the same orientation. If its < 0 the intersection was a false positive then. http://www.blender.org/api/blender_python_api_2_60_1/mathutils.html?highlight=vector.dot#mathutils.Vector.dot

Vectors have same oriented direction if their cross product is zero and dot product is greater than zero. There's no need to test the direction (the vectors are on a line), so the orientation test should be enough.

Jerryno, I only have a question about the statement "up.rotate(bpy.context.scene.objects['SUN_NAME_HERE'].matrix_world)". It seems to be location-dependent. If I move the sun to another location (which is irrelevant since we are dealing with the sun, and the ray remains the same), the values of "up" change. Further, I have made some detailed tests and it seems that the visibility test is wrong in some cases. Do you know if this statement is correct?

I am sure the rotate() func is not location dependent even if the input is world-matrix. It also takes Euler class which you can get with matrix_world.to_euler() but it will (should) yield the same result. Values of up will change everytime you call rotate() on it, it actually changes the vector forever. I am grasping at straws now, if you could post relevant parts of the code somewhere it would help

Jerryno, you are absolutely right. I am sorry, I had two odd bugs that misled me, which I have solved now. Thank you once again for your help.


text:
How do I draw onto video with Grease Pencil in the VSE?
I'm doing some video editing and would like to be able to draw directly onto the video in order to highlight objects, produce arrows, etc. It should be possible to do this with Grease Pencil, but I can't figure out how. How do I do this?
Looking for other people who've done this, it seems that it can be done, but I can't find any instructions. The obvious thing (drawing on the video with D held down) just creates an annotation rather than adding a Grease Pencil layer, and annotations seem to be ephemeral and are intended for notes to the editor rather than actual video edits --- I'd also expect them to belong to a strip, which they don't. I have found a few references to people who've created a 3D scene with the video projected onto a square and then used the 3D Grease Pencil to draw on that,  but that seems... wrong. Also, this appears to be for Blender 2.7.
But I keep finding refrences to people who've actually done this, so it does seem to be possible. Can anyone tell me how?
For reference: this is with Blender 2.82. I know that Grease Pencil has had a major overhaul since 2.80.

Yes, the grease pencil was rewritten completely in version 2.83, but as far as I know, it   works only for the 3D environment.  So most likely those who are doing what you want are compositing/overlaying the images from the scene over background video or images. If you go that route it would be easier to use the video as camera image, you don't need a plane with the video file as texture.

This means I'm effectively creating an animation where the video is a source for one of the animation elements, though, right? So I have to edit the two separately, and can't apply video effects to the drawing. I suppose I could create an additional scene and add that as a video strip, but then I can't draw on the video?

Read: Live action footage and grease pencil animation

Afaik, annotations are not for output, but only for notes inside Blender and therefore can't be added to the exported video. However you can draw with grease pencil in the 3d view in a new scene and add that scene as a scene strip to the sequencer(check transparent and change blend mode to alpha over), and that will be in the exported file.
Btw. same question here: Grease Pencil to Video Sequencer
How to draw GP on top of video:

How to add a grease pencil scene to the vse:

Size isn't the problem. They move too quickly, they can't be paused, and your setup isn't laid out the same as mine is, so trying to figure out what's actually going on is very frustrating. If you have a pointer to instructions in the form of text I can read, that'd be so much better.

Take note that this does not work when you have edits in the VSE. Have a look at https://blender.stackexchange.com/questions/328176/streamlining-video-editing-using-grease-pencil-directly-on-vse-footage and this new idea suggestion https://blender.community/c/rightclickselect/YVyM/


text:
Ignoring a channel when removing gaps in the VSE
I've got this:

I want to remove that gap, moving all strips to the right up to fill it. Normally I can do this by pressing backspace, but I can't do that here because of the audio track above --- Blender doesn't think that's a gap.
Is there any way I can tell blender to ignore the audio track while removing gaps?

I think I've found a solution. I don't know if it's the best solution, but it does appear to be a solution.
Place the playhead in the gap. Select all strips to the right. This won't select the audio overlay because it doesn't start to the right of the playhead, but it will select everything else. Then Grab, and manually move left so it overlaps the strips to the left of the gap. On confirmation, the two strips to the right will have been moved so that there's no gap, and every other strip will have been removed the appropriate amount.
If, however, I come back in ten minutes discovering that everything's been garbled because all my carefully placed overlays and crossfades have been rearranged, I will scream here, and you'll know it didn't actually work.

Check out the addon Blender Power Sequencer. Pressing C will do that for you.

That looks like it only works on one channel at a time, though, which I don't want --- I have lots of other strips (mostly text overlays) in the three channels between the audio/video and the sound overlay which need to be moved appropriately.


text:
How to join two objects.
I have two objects that I want to join together on one plane and am having dificulty figuring out how to do this.
I started by mirroring an object I had designed and I want to put the two mirrored halves together, without changing the shape of either.
I am aware of mergeing, but that changes the shape of the objects, which I don't want. I have also tried using various "snaps" none of which have resulted in the desired outcome.
Is there a way to move one object so that the center of a selected face is moved into contact with the center of another selected face, while preserving the shape of the object that is being moved.

Did you mirror manually and now have two objects - left side and right side? Why not using Mirror modifier for mirroring?

I used the mirror modifier, I might have set it up wrong but this is something I would like to know how to do regardless, if it is possible.

If all you want to do is just to move mirrored sides to each other then redo that with Mirror modifier added to one of them, it'll be much easier. If moving mirrored sides manually there should be used snapping 3D cursor to desired face in Edit mode and moving object to cursor in Object mode. See some examples with snapping as well https://blender.stackexchange.com/questions/39784/snapping-two-objects-by-edge-in-object-mode and https://blender.stackexchange.com/questions/36812/how-do-i-snap-one-vertex-to-the-position-of-another-vertex-in-a-different-object


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Use rayCast() in none-game scripts?
I want to make a scripts that adapts meshes and I need to cast rays for this.
But the rayCast() function is part of the game engine and it seems these functions can not be used by the standard scripting.
IS there a way I can use the rayCast() function?

It's not really clear what you mean by "adapting meshes". Perhaps you can add a picture or explain it more?

Blender can cast rays outside of the game engine, best ask a more specific question.


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Create a new UV map but move the textures with the polygons?
I've imported an object from an 3d data capture program in Blender, which came with an automatically generated UV Map. I'd like to create a new (more sensible) UV map based on the cleaned-up geometry, but keep the model looking the same (so the polygon-to-pixel-colour mapping is consistent).
Is this at all possible to achieve?

If the two UV maps reside on the same mesh you can use UV baking. If you create a material with the texture and the first uv layer, you can bake the diffuse color (or even the rendered result, if you make a shadeless material) and bake it to the second UV layer. Make sure to select the proper UV layers in the material texture slot, UV editor and active UV layer.


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Showing X3D color per face?
I have an X3D from Meshlab which has color per face, It's a polyhedron where per face colors are the best compared to per vertex.
Can blender show X3D per face colors? I have found an option of per vertex colors in New Material>Options, is viewing per triangle colors not implemented?

related: http://blender.stackexchange.com/questions/30314/file-format-with-per-face-colors?lq=1

related, same thing happens with .ply files: use the Vertex Color layer: Import PLY doesn't display vertex colors
In Blender there is no color per polygon, but you can set all vertices of individual polygons to the same color. When vertices are shared by multiple Polygons their vertex_color information is not.
If the .x3d is formatted correctly, then Blender will make the appropriate vertex_color map (tested! for instance with this file).

Thanks alot for the tips, i had a go to find the node arrangement and i lost the materials window i will have another go today.