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Can I use a geometry node to select or modify the material of a single object?
I have created stage lighting setup, and a lighting dimmer board with 126 buttons for selecting the channel of specific spotlights (7 buttons each for 18 lights).
I would like each button to glow when it is pushed down (i.e. moved along its z-axis). At first I was thinking of using a driver to change the emission of the material, but that would mean making a separate material for each button!
Is there a way to use geometry nodes to either change the emission of a single object according to its z coordinate?
Or perhaps selecting a different material slot may be more straightforward. Could I create a different material for button up and button down, and select the material slot according to button location?
I am new to geometry nodes so have very little idea of the capabilities or use. Any ideas or suggestions about where to educate myself would be most appreciated.

To address your question specifically:

Can I use a geometry node to select or modify the material of a single object?

Yes, of course this also works with Geometry Nodes.

In this example I have a button consisting of two elements:

The Button
The LED

I combine both objects using Geometry Nodes.
Additionally I created a Group Input, which can be controlled from outside by Driver or similar.
This float value transforms the rotation of the button on the one hand, and the light of the LED on the other hand.
For this I use the node Compare with the setting Greater Than. As soon as the button press reaches a certain value, I store a boolean value with Store Named Attribute into the geometry of the LED.
This value can then be queried in the shader and used to control the Emission.

+1 Nice solution as well. I didn't go for Geometry Nodes (which of course can do such things) because the premise of the question was that he thought of creating a material but thought he had to make a separate material for each object... so I showed a way to do it with a single material for all objects.

@GordonBrinkmann Thanks! Since Geometry Nodes store an additional attribute in the geometry here, it is of course also possible to use only one material. The shader ultimately decides here which part of the geometry gets which appearance.

Yes, sure there's only one material needed ;) As I said, I know GN can do a lot of things, it was just that if somebody isn't so experienced in GN as the OP himself stated, it wouldn't matter since you can do it completely without GN.

@GordonBrinkmann You hit the nail on the head: You can actually do almost everything without Geometry Nodes. But with Geometry Nodes it's much more fun in my opinion :D

Definitely :) But I've been working so many years without and it's still also fun to see the capabilities of the Shader Editor ;) Although I have to admit I never used the Attribute node very much and didn't know you can enter data paths there... or I forgot about that.

very nice button! ;)

I marked this as the best answer as it answers the question in the title so may best help others ending up here.
In fact, I will use my solution, based on Gordon's as it's the simplest for me to implement. I really need to study geometry nodes but ... not tonight :-)

//EDIT: If you want to be indenpendent from global positions/rotations, you will find a solution with shape key and driver below.
When the Z coordinate is the only thing that matters for the decision, you can do this with a single material for all objects.
Go to the Shader Editor, take an Object Info node, plug the Location output into a Separate XYZ node. The Z value goes into a Math node set to Less Than with the desired threshold value. The result goes into the Emission Strength of a Principled BSDF or whatever you use to make the button glow. (I multiplied the result with 10 to make it brighter).

Now for the solution that's indenpendent of all global positions or rotations.

Join the button (not pushed down) with the housing by pressing Ctrl+J. Go to the Object Data Properties > Shape Keys and press the Plus button twice to create the basis and a key.

Go into Edit Mode, select all faces that belong to the button and move them down into the "pushed" position. Now switch back to Object Mode.

Go to the shape keys again, select the key, right-click on the Value field and choose Copy as New Driver.

A little further down you'll find Custom Properties, click New and on the created prop value you can right_click and choose Paste Driver. You can also rename it to your liking by clicking the cog symbol to the right. You'll need the name in the material later, I called it "push".

In the material, add an Attribute node. Select the Type: "Object" and enter the Name you have given to the property, in my case "push". Connect the Fac output to a Math node set to Greater Than. If you now change the value of the shape key between 0 to 1 "pushing" the button, the value will be compared in the Greater Than node to the threshold value and switch on the emission when exceeding it. By the way: yes, you can paste a driver directly into the Math node without the need for a custom property. But when I tried it, one shape key controlled all glow, no matter if the other buttons were pushed or not. Therefore the custom property as a workaround.

Since the shape key and the material using the driver are completely independent from location and rotation of the object, the effect works always no matter where and how you place it.

Thanks @Gordon Brinkmann - that's a great start. You're right about the global/local issue. In fact my board is angled at 15 degrees so I'd need to local coordinate. I'll look into it.

@Thailandian I'm working on a solution for that and edit this as another option in my answer ;)

@Thailandian I'll leave the "global" solution as well, but I think my edit should do what you need.

Brinkman - Thanks, I had just come up with a similar solution, but instead of using a shape key, I just copied the RNA attribute of the object's location into the node and used the Vector output. I'll post my answer below as an alternative.

@Thailandian I have no idea what the RNA attribute is :D

neither did I until a couple of days ago! They're really useful in drivers.

Here is another solution, similar to Gordon Brinkmann's original idea.
Similarly to Gordon's second solution, I replaced the Object Info node with an Attribute node. This can output any RNA attribute value of an object (amongst other things).
To get the RNA attribute, right-click on that field - in my case the z coordinate in the Transform fields, and select "Copy Data Path" from the context menue.

Then I used Vector output of the Attribute Node to control the Emission Strength.
The emission is now dependent on the local z coordinate, and the parent's location rotation or scale has no impact.

Ah, you can put the data path in there as well. Didn't know this is called RNA attribute. So you found your own solution ;) The only advantage my setup has: you can model the button as one piece and don't have to duplicate two or more objects.

@PPL I didn't copy or paste anything since this is not my answer.

Sorry Gordon Brinkman I meant to ask the author of the solution. @Thailandian are you saying the 'copied' datapath was pasted into the 'Name' field of the Attribute node? I see you copied it but wasn't clear where you pasted it into

@PPL Sorry for the slow reply - ironically, my computer has been down for the past 2 weeks! To answer your question, I now realise it's not necessary to paste the datapath into the Attribute Name field (although it does work). Easier is simply to write "location" into the box.


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How to generate a realistic fluid sim splash?
I'm trying to have an object splash into a fluid, but I've been getting pretty strange results out of my fluid sim. The most frustrating is the effect in the gif below, where the "splash" awkwardly clings to the object before "evaporating:"

This is with a final rendering resolution of 250 and the domain settings below:

Is there any way to get a bigger and more realistic splash out of this scene? The impact factor of the obstacle is currently at 1.5.

There is a relatively high quality open source fluid simulator, called mantaflow. Site: http://mantaflow.com/  You can download it built in Blender here:http://graphicall.org/

Alternatively you can either built or buy a version of the Flip-Fluids Addon

Thank you! I've been struggling with splashes in mantaflow as well. Is it true, then, that the built-in fluid sim will not be able to generate this effect without the strange artifacts demonstrated above?

source: Stack Exchange

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

sort: votes


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Moving hook stretches edges in cloth sim
I attached two vertex pins and then two hooks for a cloth simulation on a plane. When I move the hooks, the cloth stretches the vertex's connected edges to the location of the hook, making the cloth look stretched. How can I stop the hook from stretching the edges?
This a screenshot of the first couple frames of the cloth simulation. The left hook is unmoved and correct. The right hook has been translated left.

This is likely related to https://blender.stackexchange.com/a/83096/29586 - ie, the sequence of the modifiers in the modifier stack. Ensure the Hook modifiers are above the cloth sim modifier - otherwise the cloth will apply first (to the unmoved vertices) and then the hook modifiers will move those vertices after the sim - rather than the sim taking account of the new location of those vertices.

EDIT I've put together a test and this is working as I would expect - ie, with the hook modifiers 'above' the cloth simulation. Here's the setup :

The 'cloth' consists of a subdivided plane. I have added a Vertex Group named 'pin' and assigned two vertices on the top edge to it. I selected each of these same vertices in turn and used Ctrl+H to 'Hook to New Object' to create two new empties hooked to those vertices. Note : It's important to use the exact same vertices for the vertex group as is assigned to the hook.
Using keyframes I animated the right-hand empty.

This produced the following animation :

This only works with the hooks above the cloth simulation in the modifier stack.

Blend file included

Unfortunately, this is not the case. The cloth sim is at the bottom of the modifiers stack. If moved to the top, the hook will move the vertex but not affect the rest of the simulation. When at the bottom, the cloth sim performs the behavior above.
What's frustrating is the hooks will move perfectly while the sim is running and affect the cloth sim as expected. But once the sim resets, the stretched edge effect above occurs.

Hi @xcelspreadsheet - I have performed a test and find this to work. This appears to be working correctly with the Hook modifiers above the Cloth sim in the modifier stack. I've updated the answer with the specific steps taken and have included a Blend file. I'm not sure what you mean by 'once the sim resets'... are you perhaps moving the vertex manually while the simulation is running rather than keyframing the animation - that would certainly cause problems as the animation would effectively 'bake' as it ran through the first time and would ignore changes as it looped back around.

I was moving the vertex manually using the hook attached to the empty, yes. That explains it! Thank you for taking the time—it helped a lot.

How did you connect the vertex to the Empty object, even though you did not assign the vertex group to the hook modifier?

@bakuiseok In Edit mode you simply select the vertex you want to hook and trigger the ‘Hook to New Object’ modifier as described. This automatically creates the hook on that vertex and creates the empty for you. You do not need to manually create a vertex group.

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

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


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How to scale an extrusion from a rectangular plane equally along all four sides?
I'm trying to create a very basic shape in the image of a beveled mirror. To do this, I create a plane, extrude from the plane, and then scale the extrusion. However, the beveled edge is deeper on the shorter sides than the longer sides. Dividing the plane into two faces doesn't seem to help. Any ideas on how to create an evenly-sized beveled edge?

Dissolve the extrusion and bevel the top plane instead. Scaling will never be the same for the sides of that plane unless you scale by X and Y axes separately. If beveling gives the same result then see https://blender.stackexchange.com/questions/12288/why-are-the-longer-edges-being-beveled-more

I think it would be easier to start with the bigger plane and then inset (i key)

Related https://blender.stackexchange.com/questions/7298/why-is-it-important-to-apply-transformation-to-an-objects-data and https://blender.stackexchange.com/questions/14868/inset-in-blender-not-coming-out-even

Scaling works relative to every single axis.
X is 200cm, 75 percent of that is 50cm smaller than before.
Y is 100cm, 75 percent of that is only 25cm smaller.
Use inset (press 'i') instead - it works with a fixed offset - and move the new face after that.

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Check if vertex lies within closed volume
Is there a way to check if a vertex (or for that matter, any location) is inside the closed volume of some object?

Use a BVHTree (https://docs.blender.org/api/2.79/mathutils.bvhtree.html) and get the nearest face(s) from the location. The find nearest functions return location, normal and face index. So from that you can check if the location is inside or out depending on the normal orientation returned. I'm not sure this handles all the possible configurations though.

Related (possible duplicate)

If you would like to see inside your objects, you can enable wireframe view by pressing Z. You can also hide some objects in your Outliner to see which object can be overlapping

Thanks batFinger, that is exactly what I was asking for! I guess my question can be deleted.


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I'm unable to see the mesh anymore. It's turned into a long flat plane
was making a basic mesh and whilst merging some vertices after mirroring my mesh something happened and I'm unable to see the mesh anymore. It's turned into a long flat plane. I can move the single vertex that I can see in the screenshot in any axis (https://i.sstatic.net/NxHkU.jpg) but if I move it out of that random dark plane I'm unable to see the vertex anymore. Even the default lamp and camera are non-visible when not looked at through the dark plane. I stored a backup mesh in another layer before I mirrored my mesh but the same thing appears on all layers too. Any info would be appreciated, thanks.

Some additional pictures showing the modifier stack could help

Not sure why the mirror modifier isn't showing up but here's a screenshot. (https://imgur.com/a/XaU1e)

Done. Are the rest of the images needed? I don't want to inconvenience people by posting too many images.

Yep, the cone clipping solution worked for me too. Thanks for the help, definitely wouldn't have found it on my own :)


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How do I fit these clothes onto my base mesh?
So I have this mesh that I've already rigged, and I want to add clothing to it.  But, the clothing I downloaded from a mesh-sharing site doesn't exactly fit my mesh:

Do I have to modify the dress mesh manually, or is there an easier and more efficient way of getting the dress to fit my character?

Perhaps try a Shrinkwrap modifier set to ‘Project’.


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How to check if an object at on a specific position/how to get the position of an object
I'm working on a project and I need to get the position of an object (not necessarily by python code) and at the same time I need to know how I can check if the position is on a special point like (0,3,6) for example. How can I do that?

I actually found out now, if someone needs to know, this is how I get the positions:
import bge
import GameLogic as g
cont = g.getCurrentController()
own = cont.owner
pos = own.position
x = pos[0]
y = pos[1]
z = pos[2]
and this is how I check for them:
if x = 3.0 and 2.5 and y == 3 and z == 2.5:
    print("The object has the coordinates (3.0|2.5|2.5)")

Equal checks are no good idea. Due to imprecision of the number representations the object might be very close. Better calculate the distance to the reference position and check if the distance is inside a certain range.


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How do you apply the object transform so that scaling the object on a single axis actually scales along the correct axis?
I am trying to scale an object along the Y Axis (flipping it by -1) but I am having trouble. When I scale it by Y, it seems to be a semi-arbitrary axis. The 3D cursor shows that the object's orientation is not aligned with the world, but I want to scale it on the world's Y Axis. I've tried clearing and applying rotation but it doesn't seem to be doing what I expect. I would think that clear rotation would be what I'm looking for, but it doesn't seem to work. I want the object to stay in the same exact world location but I want its rotation to be 0,0,0. How can I zero the object's rotation without affecting its actual position/rotation?
Thanks,
Warren

Are you typing "S" then "Y" then "-1", "return" and not getting what you'd expect? That's strange, because scaling along an axis should already use the world's - not the object's - axes (unless you type "Y" twice). Can you provide some screenshots?

@NicolaSap - Yes, that's what is happening. The transform location and rotation are all set to 0's but the 3d Cursor shows a non-aligned set of axes. Seeing if this image post works:

Oh, I see where it is -- Delta Transform... Now how do I apply that and zero it out?

I figured out one way to do it -- manually copy the delta transform rotation into the regular transform, then apply the rotation. Is there a better way?

Well, I'm not sure how to reply. However I'd suggest you to edit your question with the new information that you've found, in order to get new and more relevant answers.

The problem I had was that the "Delta Transform" in the object properties contained rotation.
My solution was to:
1: Apply the rotation with CTRL-A (Should leave Transform at 0,0,0)
2: Copy Delta Transform's rotation values (x,y,z) to the Transform of the object.
3: Clear the Delta Transform (just set it to 0,0,0).
Now the delta transform is clear, and scaling will work in world space.

If there is a way to do this automatically (ie "Apply delta transform") please let me know.

It's possible the other way around, converting transform to deltas (in Ctrl+A menu as of 2.78). One can clear deltas with Shift+Ctrl+action (R for rotate and so on). I'm not sure if you can copy them back to transforms and clear delta at once.

Please try this : in Object mode, hit Ctrl + A, in resulting menu select Rotation

Its all zero now, I hope it help you :) best of luck

Hi @BlenderForYou, thanks for your response. I would have expected that to work, but it does not unfortunately. Somewhere there must be a hidden transform that is not being applied. :/

Did it fixed the rotations to zeros?

It fixed the rotations to 0's, but my problem was that there was rotation in the "Delta Transform" in the object properties, which I didn't know existed.


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How does one extrude an edge relative to the vertex normals?
I am trying to flare the opening to a relatively complex organic shaped piece of geo. I'd like to extrude out from the opening, and move the extruded edge relative to the vertex normals.
I've tried extruding then pressing escape, but this makes the new edge's vertex normals point towards the center of the object so when I use Alt-S, it doesn't quite move the verts relative to the connected face.
This is relatively hard to describe so maybe some images will help. Original mesh with normals:

Then I hit alt-E and press escape. The new vertex normals point away from the origin:

Here's a close up of a vertex whose normal is facing away from the center:

And finally here's what I get when I press alt-S (was hoping for it to move perpendicularly):

So is there a way to add a sort of flared opening where the flared angle is relative to the face it's built off?
Thanks,
Warren

select the boundary edge loop using Alt+Right click (if it doesn't select the entire loop, select everything with A and click on Select > Select Boundary Loop) :

expand the selection using Ctrl++ :

while the Pivot Point is set to anything else than Individual origins, use the Extrude Region (Vertex Normals) operator :

add to the selection the extruded face loop you don't need (the lower one) using Shift+Alt+Right Click and delete the selection :

select the edge loops between which you have a gap and bridge them (Ctrl+E) :

select everything and recalculate the normals with Ctrl+N :

You get something like this :

Sorry for taking so long to respond. Am I looking in the right place for "Extrude Region (Vertex Normals)"? In the Tools panel, under "Mesh Tools", under "Add" I see an "Extrude" dropdown, an "Extrude Region" button, and "Extrude Individual" button. "Extrude" only has 2 options: "Edges only" and "Vertices Only".

Ahh, I see that option if I am selecting faces, but not if I'm selecting the edge loop as vertices. Is there a way to do that with vertices?

I edited my answer, tell me if you still have any problem

OK, the result I've been getting is using the second method you mentioned with shrink/fatten. I believe the normal it uses is towards the 3d cursor or the center point of the object. If you shrink the opposite direction, you will probably see all the vertices come together at the center point.

The first method you mentioned is the closest to what I've been looking for. Thank you! However, I will need to clean up my mesh to have a full face loop at the top ring. It's not a super clean mesh because it is taken from a 3d scan of my foot. I can see though that method will work if I clean it up.

I re-edited my answer to make it work on messy triangular meshes.
You're right about the Shrink/Flatten method, it uses the object's origin once you extrude the boundary edge loop, because since the extruded vertices are overlapping with the non-extruded ones, their vertex normals have no clear direction anymore, so Blender uses the object's origin instead. So this method is not valid and I removed it from my answer.

That's awesome. The only thing I had to look up was how to get the Edge menu up (Ctrl+E). And I can see how repeating this method can allow me to create a new flared opening at any angle! Thank you!

added precisions in steps 1 and 5


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Cannot Set Material to Metaballs
I'm still fairly new to Blender and I have a question I cant seem to find the answer to. I'm trying to make this low-poly bonsai tree by creating leaves with Metaballs but I can't seem to set the material for the Metalball groups.
As you can see, the material field is blank. I don't know if I'm doing something wrong, or I haven't turned on the proper settings. Please help! Thanks :)

Two quick issues, I can see here

You are using Blender render, please switch to Cycles render
your Properties window for the materials has been scroll down, please scroll up to see the option.

@cegaton : Agreed with you, just giving him both option, if he like :)


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How to achieve dynamic cloth pinning?
I'm having trouble trying to understant how cloth simulation pinning works. I want to modify the pinning group during animation so that I can have characters grabbing and dropping pieces of cloth without interrupting the flow of the simulation. For this purpose I tried to use dynamic paint, but it seems like once the animation starts playing you can only remove vertex from the pinning group, not add or modify them.
The red ball in the exmaple below paints vertex red and the blue ball deletes paint.

What is the problem here? Is there a workaround to this so that cloth can be pinned and unpinned mid-animation?

I have had the same issue in 2.81a. This might be solveable if magnetism on "every point" could be adjusted with vertex groups, similar to cloth physics or other modifiers. Will suggest to developers if possible.

There is no simple solution to this.
Animating the group itself is not a problem, you can use the AnimAll addon or just stack multiple vertex groups with the Vertex Group Mix modifier where you can animate the influence of participating groups on the final one.
The problem is that when you need to change the pinned vertices, you need the simulation to continue where it ended the frame before. But the simulation will not pin the vertices where they currently are, but where they were before the simulation started. Those newly pinned vertices would just jump from frame to frame to their un-simulated location.
To solve this in Blender, you need to create multiple simulations that closely start where the previous ends (and they need to start-end with similar motion also). Then you need to create one extra mesh so you can interpolate between all those simulations and smooth merge them into shapekey animation:
How to bake softbody animation into keyframes?
You will have to modify the script to sample from multiple meshes and to smoothly transition between them, but most of the code is there.
When sampling the simulations you take locations from first simulation and when you approach the second you smoothly switch to it's vertex coordinates.
The results can be very good and convincing. It is common practice in many simulation applications when the simulation is not precise enough like you want and you need to hand sculpt some key poses of the cloth into the simulation.
If you want to avoid the scripting, you can also use multiple Mesh Deform modifiers to those simulations and then blend between them with influence. But when your simulation changes, you can simply re-run the script while otherwise you need to rearrange, re-bind and re-animate those modifiers.

the animAll addon in the addons contained in blender. This addon will allow you to animate the group of vertices that is pinned to the cloth.

Sadly this won't work, because when changing the pinned group it will not take the location from the simulation but the old location when the mesh was static before simulation. It results in non-smooth simulation and sudden jump frame to frame.

Will the hooks help here? How about parenting vertices individually?


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Can Blender support something like OpenTimelineIO?
I am an animator who use Synfig (animation) alongside Blender (video editing) and Ardour (audio editing). Though I use some linux-specific scripts and commands to have a common workflow between them, I often create multiple renders, for even for single simple projects, taking awful lot of time. It could be avoided if Blender and other required apps use something like OpenTimelineIO (https://github.com/PixarAnimationStudios/OpenTimelineIO). Is it possible?

It's possible to write an add-on for this, yes. The question whether Blender can support this is unfair, though. It's more a matter of finding people interested in implementing it.


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How to create fan blades?
How do I make these fan blades for a jet engine? These are the blades I'm wanting to make. thanks
Here is the engine so far in blender

Related https://blender.stackexchange.com/questions/40211/modeling-a-3-blade-boat-propeller and https://blender.stackexchange.com/questions/86429/how-can-i-model-a-propeller-like-the-one-in-the-image

Here's 2 videos of how to do it... I would tell you how to do it in an answer but I can't right now... Hope these help. https://youtu.be/Oivgs0vzy8o is a traditional modeling method and https://youtu.be/YRgcXnd1Wl4 is a tutorial about the spin tool. The spin tool tutorial isn't specific to fan blades, but it could be a starting point for you if you decided to make it that way.


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Blender's cube projection unwrapping doesn't work anymore in Unity
I have Unwrapped my level in Blender using the cube projection Option. the results were exactly what I wanted
The level looked also looked fine in Unity for a while. However I'm not sure what happened but right now unity is not unwrapping them properly
Besides unwrapping every single texture manually I don't know what to do and I would definitely need some help. Thanks in advance!

Is the texture still correct in blender? Did the mesh change? How are you bring it into unity?

Did Unity add on extra materials to your mesh? Open up the mesh renderer and check. I think if you change it to 0 and assign your grid texture, that should do it. Another thing you could try is delete the model/texture from Unity and re-import them.

I have solved the problem by finding this link:  https://answers.unity.com/questions/826967/textures-on-models-messed-up.html    Apparently my texture has been set to "clamp" instead of "repeat". I'm not sure why though. I wanna say thanks again for commenting


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frame_change_pre.append(handler) doesn't work
I wanna run a function each frame. So I create a new script and type in the following:
import bpy

def my_handler(scene):
    print("Frame Change", scene.frame_current)

print("test")
bpy.app.handlers.frame_change_pre.append(my_handler)

The problem is, that it simply doesn't work. When I hit "Run Script", "test" is written to the console, but nothing else happens then.

The hander "fires" when you change frames. What happens when you scrub frames or animate?

Oh, I thought it fires each frame of blender... can I do that somehow?

I found it: bpy.app.handlers.scene_update_post.append(my_handler)

From link below: "By default handlers are freed when loading new files. In some cases you may want the handler to stay running across multiple files (when the handler is part of an add-on for example)."
You may need to use the persistent decorator:
import bpy
from bpy.app.handlers import persistent

@persistent
def my_handler(scene):
    print("Frame Change", scene.frame_current)

print("test")
bpy.app.handlers.frame_change_pre.append(my_handler)

see https://docs.blender.org/api/blender_python_api_2_60_6/bpy.app.handlers.html


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How do you create an aura, or halo effect, like what was possible with the internal Blender Render Engine, in 2.80
When Blender had its internal render engine, you could set it to render objects as a halo, rather then as a solid. It also allowed for starburst and other effects in the halo. I would like to know how to do the Halo effect using Blender 2.80, preferably in Cycles. I doubt there is away to add the other effects that were possible.

I don't want halos from particles, I want the mesh it self to emit the halo effect., like in the old internal blender render. I don't want to have to set up a particle system at all.

A similar question was asked a little while ago. The following answer should provide you with the information to render halos in Cycles: (see 'Point Clouds').
https://blender.stackexchange.com/a/45487/23799
Since the linked answer is over a year old, I went ahead and verified it's content for Blender 2.80 and expanded upon the explanation on how to set this up.
For further reference on this method, see the aforementioned post.

As an example, I've added a mesh that will represent the location of the particles in the particle system. Add a particle system to the mesh and leave the settings as is.

Add a mesh that completely encompasses the particles in the particle system. This will be your volume shader. Create a material for this mesh and open the Shader Editor.
(I have made the cube semi-transparent so you can see what's going on inside).

In the Shader Editor, detach the Principled BSDF Shader node(or delete it) and add a Point Density shader (Add > Texture > Point Density) and an Emission shader (Add > Shader > Emission).
Connect the Density output of the Point Density node to the Strength input of the Emission shader.
Then connect the output of the Emission shader to the Volume input of the Material Output node.
Set the nodes up as follows; In  the Point Density node, select the object to which you added the particle system(in this case, Suzanne) and select its(her?) particle system (called 'ParticleSettings' here) in the Particle System input below. Leave the other settings as is.

Now, if you render the image using (Viewport) Render, you'll see the particles glow up. You can change the size of the glow by changing the 'Radius' setting in the Point Density node.


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I need to show my poly count in my render for a school assignment. How can I do that using Blender 2.83?
I modeled a well for a school assignment using blender 2.83. I need to make a render which shows the poly count. I can't find polycount as an option in the Metadata to include in the render. I wonder if there is a way to include it in the render or am I going to have to add it in the notes after getting them.

related: https://blender.stackexchange.com/questions/174158/show-the-polycount-of-selected-objects-in-object-mode

Just add it as custom text/name in the metadata options.

Poly count is at the very bottom right of the screen.
In the note section for metadata write the info you want and turn on "burn into image"

A different way to see statistics is to enable the overlay in the 3D viewport as shown in this post:
Bottom Status Bar Doesn't Show Verts, Faces, Tris Information In v2.9a

Here's a script to automatically write the with the selected object's stats on the metadata notes:
adapted from :
Show the polycount of selected objects in object mode
import bpy

verts, edges, polys = 0, 0, 0
dg = bpy.context.evaluated_depsgraph_get()  # Getting the dependency graph
for obj in bpy.context.selected_objects:

    obj = obj.evaluated_get(dg)
    # This gives the evaluated version of the object. Aka with all modifiers and deformations applied.
    mesh = obj.to_mesh()  # Turn it into the mesh data block we want

    verts += len(mesh.vertices)
    edges += len(mesh.edges)
    polys += len(mesh.polygons)

bpy.context.scene.render.use_stamp_note = True
bpy.context.scene.render.stamp_note_text = "Verts: "+str(verts)+", Edges: "+str(edges)+", Polys: "+str(polys)
bpy.context.scene.render.use_stamp = True

To use go to the scripting window, create a new text, paste the script and run it.


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Distorted UV unwrap issue
I am trying to UV unwrap a model of a tank I am creating. I am having an issue trying to unwrap the tank body. It is basically a box with a curved front and back. I am trying to do a seamless texture all the way around, so I split the body in half so that I could unwrap it, then duplicate it and flip it so the UV coordinates are mirrored. When I press 'u' and select "Unwrap," I get the following result:

As you can see, it's a continuous row of quads with two open ends, so I see no reason why it shouldn't unwrap in a more straightforward fashion. I looked around for solutions already. I tried applying the scale, which made no difference. I tried resetting the UVs from the 'u' menu, then unwrapping again, but that still resulted in distortion. I already removed doubles. I would set up some seams, but given the shape I have I don't see how that would help at all. Maybe if I re-created the geometry it would work, but then I don't understand how it would get stuck in this state.
How can I unwrap this so that each face keeps the correct proportions and the edges are aligned to X and Y in the UV editor?
Here is the blender file if that helps: simple tank (unwrapped).blend
Thanks.

You have pinned vertices. Here are two images which describe how to fix the issue.

Fantastic. Not sure how it happened to begin with, but that fixes it. Thanks very much!


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What is the best way to send operation from a software to blender?
I want to make addon with C++ and Qt (like arnold renderer) or with python and PyQt/PySide and run blender python scripts. I don't want to make addon in Blender python api. I found some ways but i don't know which way is better or if there is an other good way or not. Please help me do this.
some ways i found:

install PyQt/PySide in blender's folder (i don't like this way!)
make server and client and send operations to blender
make loop in blender to check a file and write operations to file from app

TL;DNR: There is no best but Client/Server is used most often so I would recommend that approach.
There is no single best way, because all of the approaches have strengths and weaknesses and the one that works best in a given situation will depend on which weaknesses your application can tolerate.
Since you don't like the first approach I'll only comment on the other two.

Client/Server approaches are the most flexible and allow you to have the client and server on different machines; but they rely on networking libraries that can be a bit tricky to use and hard to debug in weird corner cases.  Still, they're the type of approach most commonly used in these situations.

File based approaches are subject to various problems with timing, OS buffering of file contents, and conflicts when you try to use the same technique from two instances of Blender at the same time; but they take very little code to implement.

Two other approaches that are more complex and probably over-engineered for your application are

Shared memory based approaches. These are a hybrid of client/server and file based approaches in that they tend to use mailboxes.  They're a bit more robust than client/server but also a bit more complex.

Blender as a module.  Complete overkill for your use.

That said, I would recommend client/server because there are plenty of examples; it's not that difficult to adapt existing approaches; and there's a community where you can get support.


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Use multiple Child Of constraints in one bone and animation
I have a model and rigged this model then i added 2 Child Of constraints to one of the bones and in timeline i want to change parent but when i do this , bone and attached mesh go to other place and everything runs out. How to fix it?

Could you use regular Parenting instead (of child of Contraints)? For this use Ctrl+P with two selected Objects, where the Parent is the active object (last selected) and the Child is the other Object

i want to change parenting in animation

Do you use keyframes on the influence slider to change the parent? If yes, this probably causes the problem. Because if you reduce the influence of the first parent zero, while you increase the influence of the new parent, the reduction of the old parent will set the position to the default position again instead of leaving it where it is. To solve this i think you can just keep the old parent on 1 while setting the new parent to 1. Maybe you need a different solution, depending what exact behaviour you want to achieve.


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import .fbx animation from blender to unity cause weird position and rotation
i made some animations in blender and exported to .fbx but when i import them to unity some action clips have problem.

I have read similar situations (answers, community, stackoverflow, ...)
i realized that blender and 3ds max are using constant animation FPS but unity has decimal values in FPS. and this makes problem for me.

FOR EXAMPLE
i have shotgun reload animation that shell goes into weapon from frame 10 to 20 and from frame 20 to 29 it remains there and in frame 30 (just 1 frame) i reset position.but in unity from frame 29 to 30 takes about 0.05seconds and it shows that shell returns back.(i want to return immediately)

Ways have been tried

blender exporter settings (simplify = 0, sampling rate = 0.1, and any other part in settings)
unity (turn off resample curve, reduce keyframe, and lots of other settings)
unity (change time settings in project settings)
set interpolation mode to constant in blender
export 1 animation per file in blender

but none of these ways worked for me. please guide me.

In this cases the best if you make the shell as a separate object (if you use armature, you can easily bind it to a bone in Unity) and turn off the model while it flies in unwanted locations.

What happens if you don't reset it in the last frame and make the animation start over automatically, but pause on the 1. frame (Animation Editor).

I had this issue importing my fbx from Blender to Unity. So what I did was to change the framerate from 30 fps to 29.97 inside Blender.
Then when I imported to Unity all worked good to me.


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When applying location of a translated object with mirror modifyer the global axes are used
I really don't know how I archived this. Can anybody tell me how to get the mirror modifier to use local axes when applying the object's location?

What do you want to do?

I have a tutorial video where a simple plane where cut into two half's. One has been deleted and subset with a modifier for demonstration purposes.
Then the plane is moved and the location has been applied.
On the video the mirrored part is still in position just as expected.
Every time I apply the location, the GLOBAL Axis are used for the mirror. I retried that with a simple new project but get the same result.
Q is what do I make wrong. Or is there a global Setting that I accidentally switched?

Do you have a link to this tutorial video?

It's a big german one, the part I used seems to be only buy able.
Here is a video of another part: https://www.youtube.com/watch?v=zoc9_dRcvn4

Generally the mirror modifier uses the object origin as pivot point, to mirror the mesh along global axes; when you apply the loc, the object origin goes to world origin (0,0,0).
You can create a new object (maybe an empty) and use it as new pivot point selecting its name in the mirror modifier "Mirror object" menu.
This empty can be moved and rotated along with the object, to get the mirroring performed on any desired local axes.


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Missing geometry and UVs when batch rendering through command line and Deadline
I'm trying to render a scene composed of alembics(cached geometry and transformations) on my farm using deadline, which should itself be using command line rendering anyways. When I try to command line render the scene on windows either via the command prompt or deadline, it messes up some frames, more often than not it renders a good frame and then a bad one, where the geometry disappears and uv's get messed up.
I am using Blender 2.81 on Windows 10.
any light that you can shed on why this is and how to solve it would be greatly appreciated.
I'll attach a sample of a good and a bad frame;

Looks like it is a disk mapping problem, I changed all paths(textures, files) to the mapped disk of my server and seems to work fine.


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How to bake wireframe to texture? no i'm not referring to export uv
i'm modeling an hard surface with subdivision, bevels and so on.
I would like to bake the final wireframe to texture, with all the subsurf, bevels, bools etc.
Is it possible?

Just in case you need a wireframe not baked but rendered  ... https://www.youtube.com/watch?v=ZVzWaf8ZK04

This seams to be what you are looking for https://blender.stackexchange.com/questions/51802

Ah, am I right - you want texture with wireframe that includes subsurface and bevel topology generated by modifiers without apply? Can you give us some reference image? Because like with subsurface the result would be a big mess ...

I'm not sure this is exactly what you want but you could duplicate your object, apply all the modifiers to the copy, in Edit mode/Face Select mode, select all and inset individual faces (double i), give a color to the selection, invert selection and give another color to the wireframe, then bake the result?

thank you for your suggestion, but this is a destructive method, i would like to keep my modifiers in order to easily modify the mesh if needed

what do you mean by "destructive method"? Yes you need to apply the modifiers but you can keep the original with its modifiers.

Wireframe node should be possible to bake as any other material ... it just goes to triangulated. Probably because all meshes are triangulated for rendering?

mmh sound interesting, i'll give it a try!


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How to merge 2 parts of the same object?
i have a simple question for you, i need to "merge" 2 parts of the same object in edit mode where the faces collide, here a simple example to better explain the desiderata:

IS it possible in Blender with a simple operation? or do i have to recreate the whole parts to make them collide correctly?

https://blender.stackexchange.com/questions/51318/how-to-really-make-it-only-one-object https://blender.stackexchange.com/questions/2976/how-can-i-add-vertices-to-intersection-of-two-edges https://blender.stackexchange.com/questions/28574/simple-way-to-creating-vertices-at-intersecting-planes-and-deleting-leftover-int/28577#28577

Recorded a quick video showing how to easily do it.
The steps are:

Create two loop-cuts on the smallest/thinnest part.
Snap the new loops along the X axis(or whatever axis are appropriate for your mesh) to the mesh you want to merge it with.
Select the faces your mesh is going through and create an inset face.
Scale down the new faces and snap the edges into the thin piece.
When all edges/vertices are overlapping use Alt+M and select "By Distance" to merge overlapping vertices.
Finish off by either manually selecting and deleting the interior faces or use Select - Select all by trait - Interior faces to select them and delete

Thank you, this is a good solution, but consider that my image is composed by only 1 object.

this is a simple topology, just add there a few more edges and merge the vertices. You can use voxel remesh as that is just one click operation but it makes the next modeling impossible in a classic way.


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Create a solid from 2D math function
Is it possible to create a solid based on a 2D function in Blender?
Example:
I have a function $y=x^2$ where $x \in [0,1]$. Here 'Z' is simple projection of XY plane so, extrude shall do the job.
I looked at the 3D Math addon functions but it not what I really want.
I finally want to create an stl image (attached). The attached stl is done using OpenSCAD but I found few issues like the symmetry is missing, scales are not accurate and I was not flexible in increasing the face count to have an accurate shape.

It's possible to create complicated shapes using a function using the Extra Objects addon's XYZ Maths Surface option. This allows the surface to be defined mathematically. From your sample image this isn't simply y = x^2. It's not a straightforward way of creating a mesh but it is possible. What function are you actually trying to create?

i did come across math surface but I am not sure how to define z in that case as its only a projection as you see in the fig. The function is "y=x^2/(x^2+(1-x)^2)" where x=[0,1].

You can achieve this with the Extra Objects addon, XYZ Math Surface option.
To enable the addon, open the User Preferences and search for the Extra Objects addon and enable it. Now in the Add menu you should find Mesh/Math Function/XYZ Math Surface. This allows you to define the coordinates of points in XYZ space as two variables (U and V) are varied.
To create your equation (y=x^2/(x^2+(1-x)^2)) you need to vary U over the range 0.0 to 1.0 and substitute x for u - by defining X as simply u and defining Y as u**2/(u**2+(1-u)**2) (note that power (^) needs to be written as **).

In order to turn this into a symetrical surface we need two points, one at +y and the other at -y. For this we can use V and vary it between -1 and 1 with only 2 steps (so it flips between -1 and +1 for each point) and multiply the previous equation by v :

To produce the shape in your question we need to stretch the two sides apart - achieved by adding a constant to the equation :

Finally, to add the 'ends' we can extend the range and use "ternary" operators to allow us to use 'x if condition else y' form. Here we set it effectively to 0.5 if u < 0 else our_equation if u <= 1 else 1.5. This produces the following result :

Note the settings in the left-hand panel. Increase the U step for more vertices along the mesh. Decrease U min for a longer 'handle', increase U max for a longer 'paddle'.
Once you're happy with the shape you can simply enter edit mode (Tab) and Extrude (E) to give it some thickness (or add a Solidify modifier if you prefer).

Thanks!! Is there a way to name a zone on the stl image. For example, let's say I want to name the surface of the stl as "tz" between (0.4,-1.5,-0.5) to (0.6,1.5, 0.5). I want to use this name while meshing for a CFD software (for applying a boundary condition).

@Saideep I’m afraid I don’t know how you would go about that. Perhaps ask a separate question - someone might be able to help.


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Difference boolean for overlapped objects or any possible alternative
I am trying to generate a geometry using Math Function (XYZ function) as in Fig.1  using version 2.79.
I ideally would prefer to have three independent objects and merge/join all 3 objects as one and export as an stl. I am aware of the 'join' function but this would not eliminate the overlapped boundaries in the stl file (that is the stl file still marks the boundaries of the objects present in the joined stl) which is not what I want. Therefore, I taught 'difference' boolean can be used but was causing major issues.
The steps I followed were,
Step1: Model bottom half part of the geometry as in Fig.2 (see for equation used).

Step2: Copy paste Part1 to get Part2 and rotate 180 along Y as in Fig.3. This results in an overlapped portion of the objects.

Step3: Add Part3 to finish the geometry as in Fig. 4 by copy past part1 and rotate 270 along Z. Again this has overlapped portion of the object.

Now, I extrude each object individually and select a plane to apply the difference boolean. Unfortunately, this works very rarely and most of the time I end up with an unsnapped plane as in Fig.5. How can I avoid this?

For reference, I attach the blender file with 3 objects. I have not included the extrusion of the objects and difference boolean in the .blend file to make it flexible to work for others.

Do note that, I am using a maximum number of vertices for the math function (1024) as for my purpose I would like to have accurate tangents and normals to the surface. I did try out the "remove double" but still, I have some unwanted parts in the geometry.
Thanks.

For the accuracy you mention, do you require the vertices internal to the shape, or will the vertices on the boundary be enough?

The main aim is to get the boundary of the model which later will be used for a Computational Fluid Dynamics set up. Internal vertices are less important (in other words, I don't even need them) in this case but I guess the difference boolean is struggling with the overlapped vertices.

Boolean have limitations, as described in blender wiki:

Boolean operates best on water-tight meshes, where inside/outside is
  clearly defined.
The following characteristics are known to give bad output.

Open volumes.
Overlapping geometry.
Self-intersections.
Zero-area faces.

While they may not fail in all situations, they aren’t guaranteed to
  work properly.

When you join meshes you create Overlapping geometry and Self-intersections, that makes bad result.

So make 3 separate booleans to avoid self-intersections.

Or maybe try different ways to build geometry, for example Animation nodes or Svercok ?
Or instead of using booleans remove useless parts of mesh manually, in edit mode?

Could you please elaborate on using 3 booleans? (I think it is the same doing 3 times the difference boolean one after the other or am I thinking wrong?) Also, I am not sure how to remove unwanted portion in edit mode as I have way too many vertices. I tried 'remove doubles' but not satisfactory.

I have tried the three individual boolean step mentioned above and I did notice that blender struggles to snap-off the essential portion.

I can't be sure this result is acceptable, but maybe the general approach is.

Dispose of all geometry not contributing to the profile you're interested in.
a) select 1 internal vertex then Select > Similar > By Connecting edges, and delete.
b) on all straight edges, Ctrl-select internal vertices, and dissolve.
Put pivot at center of long straight edge
a) With edge selected,ShiftS Cursor to selected
b) In Object Mode ShiftCtrlAltC > Origin to Cursor.
Create empty at origin

Assign an Array modifier in the Empty's space, and rotate the empty
in Z by 90 degrees.

This results in an offset.. (the ends of your math function curves do not meet)

So compensate with an offset in the modifier, as shown

Hoping this is what you are after - corners now coincident

Make the outline contiguous, after applying the modifier.
a) Go in by hand AltM, merge the corner vertices
b) Delete internal vertices
c)  F Fill the outline, resulting in an Ngon face

Optionally tidy up, put the pivot at the center, put in a couple of edge-loops which meet there.
Extrude the face.

Of course, if it's the hole you want, not the block, delete the Ngons, turn the profile inside-out and box it in.


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Scaling a math function from a specific vertex
I have a model developed through a math function as shown below in the figure. I would like to scale the figure as shown in the figure without changing the vertex position.
Explanation of the figure:
The model seen is according to the function implemented. Now, the two vertices on the Y-axis remain where they are originally present and the surface of the model needs to be scaled proportionally in x,y (that is if scale factor of 2 along x, then the same scale factor 2 along y from the vertex) shown in red.

My guess is that the positioning of the origin needs to be changed but not sure how?
Any hacks to do address this?
Thanks.

I'm not sure what the best way to scale that with Blender would be, but I'd look at just adjusting your equation. Here's your $y$ equation:
$$y=\begin{cases}
0.5 & \text{if } u < 0 \\
\frac{u^2}{u^2+(1-u)^2}+0.5 & \text{if } 0 \leq u \leq 1\\
1.5 & \text{if } u > 1
\end{cases}$$
Notice that the main part of the middle equation, $\frac{u^2}{u^2+(1-u)^2}$, normally has a range of $[0,1]$ on the interval $[0,1]$. You are offsetting it by $0.5$. If we scale it, and change the offset of the third piece, we can place it wherever. Use this equation instead:
$$y=\begin{cases}
0.5 & \text{if } u < 0 \\
k \cdot \frac{\left(\frac{u}{k}\right)^2}{\left(\frac{u}{k}\right)^2+\left(1-\frac{u}{k}\right)^2}+0.5 & \text{if } 0 \leq \frac{u}{k} \leq 1\\
k + 0.5 & \text{if } \frac{u}{k} > 1
\end{cases}$$
where $k$ is your scalar. You can try it online using Desmos here. (Thanks to Rich Sedman for help with scaling horizontally).
In a Python expression, it would be this (substituting in whatever value for k):
(0.5 if u<0 else (k*((u/k)**2/((u/k)**2+(1-(u/k))**2)+0.5) if (u/k)<=1 else k+0.5))*v

Nice answer. With a few tweaks to ‘x’ you can include scaling horizontally - see https://www.desmos.com/calculator/ba7g3qpclp

@RichSedman Heh. I totally missed that second part of the scaling. I'll add that, thanks.

Is it possible to have "u Step>1024" for math function? I am planning to have a geometry as above but with 2 models (named 'A', 'B') where A is a mirror of B and both are connected to the 0.5 line. If I have a combined model as one geometry, I must compromise on precision as I cant have 'u step'>1024. If A and B are modelled independently each geometry can have 1024 'u step' and have a better precision for the geometry. So, is it possible to export A, B as individual stl images with u steps = 1024 and merge them to get the desired output?


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only PART of a spherical mesh not rendering uv texture
Newbie trying to create an eyeball. Used a uv sphere, modified it a bit, unwrapped (added seams) and all seemed good in the 3d viewport shading's rendered mode, but in actual render the center of the eyeball is not displaying the texture properly. What am doing wrong? :/

this is really hard to tell from your screenshot. could you upload your file to blendexchange? https://blend-exchange.giantcowfilms.com/

wow that was fast! the file is here:

One eye geometry is invisible in the viewport (eye outer), but visible for rendering. Open the Outliner and pay attention to the little eye and camera icons next to your objects. The eye makes an object appear in the viewport (and in rendered viewport display), the camera activates/deactivates an object for final rendering (F12 or animation rendering).

To make your eye inner geometry fully show in final render, you can either click the camera icon of eye outer and make the object disappear, or you can give it a glass shader and let the texture of eye inner show through.
In the viewport, you can use the shortcut Alth to bring back all hidden geometries and objects.

Thank you so much, and I do feel a bit silly. You saved my eye, thanks again!


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Textures after soldify?
I have created a hairstyle. When I try to soldify it to get a thicknes i can only see blurred rims. How to change it without unwrapping uv maps once again ?

If you apply the modifier, then you can just select the faces that are showing incorrectly and manually unwrap and align those.


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Blender Made an object inside my object
I am new to blender and I am trying to make a character player. I just finished creating the model and somehow messed everything up. There is a character object inside my character object. But, they are the same object. It is almost as if blender copied every vertex and re-added it slightly out of line. Looking for some help and advice. Attached is a drive link to my blender file.
https://drive.google.com/open?id=1QALbFkmGPriKuchhaha0Xx1PFYW3G2-x

Thank so much for the help! But, that didn't work. It kind of seems like the vertices are not exactly doubles of each other. It's like there is a slightly smaller person inside my bigger person. :/

If it is not too much trouble. I would really appreciate it if someone could take a look at the blender file in my original post. Explaining what happened in words doesn't seem to do the situation justice.

Well I dunno how you got into this situation, but @cegaton is right, "Remove Doubles" will help.  In this case I had to bump up the Merge Distance to .06 to remove what looks like all of the doubles, although it's hard to be certain.  And then I had to recalculate the normals.


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Physics vehicle rig twisting
I have been working on a physics based tank rig and while it mostly works, I'm having trouble making it drive in a straight line. The rig continues to keep twisting, one way or another.
Even when it's not moving I can see close up that the rig is turning on the spot. Increasing or decreasing the Rigid World settings appear to have no effect. Here are some screen shots of the tank moving in a "straight" line and a close up of it as well.

You can download the rig from here, it's a single .blend file from 2.79.
I am so close to having this rig working correctly, but I've been trying to get this final problem fixed for a while and I've gotten no where. If anyone could help me then it would be much appreciated.
Thank you.

Rigid Body Constraints
Introduction
Constraints (also known as joints) for rigid bodies connect two rigid bodies.
The physics constraints available in the non-game modes are meant to be attached to an Empty object. The constraint then has fields which can be pointed at the two physics-enabled object which will be bound by the constraint. The Empty object provides a location and axis for the constraint distinct from the two constrained objects. The location of the entity hosting the physics constraint marks a location and set of axes on each of the two constrained objects. These two anchor points are calculated at the beginning of the animation and their position and orientation remain fixed in the local coordinate system of the object for the duration of the animation. The objects can move far from the constraint object, but the constraint anchor moves with the object. If this feature seems limiting, consider using multiple objects with a non-physics Child-of constraint and animate the relative location of the child.
Connect
The quickest way to constrain two objects is to select both and click the Connect button in the Physics tab of the Tool Shelf. This creates a new Empty object (named “Constraint”) with a physics constraint already attached and pointing at the two selected objects.
Physics Tab
Also you can create Rigid Body Constraint on of the two constrained objects with Rigid Body Constraint button of the Physics tab in the Properties editor. This constraint is dependent on the object location and rotation on which it was created. This way, there are no Empty object created for the constraint. The role of the Empty object is put on this object. The constrained object can be then set as Passive type for better driving the constrain.
Additional parameters appear in the Rigid Body Constraint panel of the Physics tab in the Properties editor for the selected Empty object or the one of the two constrained objects with the created constraint.
Common Options
Rigid Body Constraint panel.
Enabled
Specifies whether the constraint is active during the simulation.
Disable Collisions
Allows constrained objects to pass through one another.
Object 1
First object to be constrained.
Object 2
Second object to be constrained.
Breakable
Allows constraint to break during simulation. Disabled for the Motor constraint. This can be used to simulate destruction.
Threshold
Impulse strength that needs to be reached before constraint breaks.
Override Iterations
Allows to make constraints stronger (more iterations) or weaker (less iterations) than specified in the rigid body world.
Iterations
Number of constraint solver iterations made per simulation step for this constraint.
Limits
By using limits you can constrain objects even more by specifying a translation/rotation range on/around respectively axis (see below for each one individually). To lock one axis, set both limits to 0.
Fixed

Panel: Physics ‣ Rigid Body Constraint
Type: Fixed

Options available to a Fixed constraint.
This constraint cause the two objects to move as one. Since the physics system does have a tiny bit of slop in it, the objects do not move as rigidly as they would if they were part of the same mesh.
Point

Panel: Physics ‣ Rigid Body Constraint
Type: Point

Options available to a Point constraint.
The objects are linked by a point bearing allowing any kind of rotation around the location of the constraint object, but no relative translation is permitted. The physics engine will do its best to make sure that the two points designated by the constraint object on the two constrained objects are coincident.
Hinge

Panel: Physics ‣ Rigid Body Constraint
Type: Hinge

Options available to a Hinge constraint.
The hinge permits 1 degree of freedom between two objects. Translation is completely constrained. Rotation is permitted about the Z axis of the object hosting the Physics constraint (usually an Empty, distinct from the two objects that are being linked). Adjusting the position and rotation of the object hosting the constraint allows you to control the anchor and axis of the hinge.
The Hinge is the only 1-axis rotational constraint that uses the Z axis instead of the X axis. If something is wrong with your hinge, check your other constraints to see if this might be the problem.
Options
Limits
Z Angle
Enables/disables limit rotation around Z axis.
Lower
Lower limit of Z axis rotation.
Upper
Upper limit of Z axis rotation.
Slider

Panel: Physics ‣ Rigid Body Constraint
Type: Slider

The Slider constraint allows relative translation along the X axis of the constraint object, but permits no relative rotation, or relative translation along other axes.
Options
Limits
X Axis
Enables/disables limit translation around X axis.
Lower
Lower limit of X axis translation.
Upper
Upper limit of X axis translation.
Piston

Panel: Physics ‣ Rigid Body Constraint
Type: Piston

A piston permits translation along the X axis of the constraint object. It also allows rotation around the X axis of the constraint object. It is like a combination of the freedoms of a slider with the freedoms of a hinge (neither of which is very free alone).
Options
Limits
X Axis
Enables/disables limit translation around X axis.
Lower
Lower limit of X axis translation.
Upper
Upper limit of X axis translation.
X Angle
Enables/disables limit rotation around X axis.
Lower
Lower limit of X axis rotation.
Upper
Upper limit of X axis rotation.
Generic

Panel: Physics ‣ Rigid Body Constraint
Type: Generic

The generic constraint has a lot of available parameters.
The X, Y, and Z axis constraints can be used to limit the amount of translation between the objects. Clamping the min/max to zero has the same effect as the Point constraint.
Clamping the relative rotation to zero keeps the objects in alignment. Combining an absolute rotation and translation clamp would behave much like the Fixed constraint.
Using a non-zero spread on any parameter allows it to rattle around in that range throughout the course of the simulation.
Options
Limits
X Axis/Y Axis/Z axis
Enables/disables limit translation on X, Y or Z axis respectively.
Lower
Lower limit of translation for X, Y or Z axis respectively.
Upper
Upper limit of translation for X, Y or Z axis respectively.
X Angle/Y Angle/Z Angle
Enables/disables limit rotation around X, Y or Z axis respectively.
Lower
Lower limit of rotation for X, Y or Z axis respectively.
Upper
Upper limit of rotation for X, Y or Z axis respectively.
Generic Spring

Panel: Physics ‣ Rigid Body Constraint
Type: Generic Spring

Options available to a Generic Spring constraint.
The generic spring constraint adds some spring parameters for the X/Y/Z axes to all the options available on the Generic constraint. Using the spring alone allows the objects to bounce around as if attached with a spring anchored at the constraint object. This is usually a little too much freedom, so most applications will benefit from enabling translation or rotation constraints.
If the damping on the springs is set to 1, then the spring forces are prevented from realigning the anchor points, leading to strange behavior. If your springs are acting weird, check the damping.
Options
Limits
X/Y/Z Axis
Enables/disables limit translation on X, Y or Z axis respectively.
Lower
Lower limit of translation for X, Y or Z axis respectively.
Upper
Upper limit of translation for X, Y or Z axis respectively.
X/Y/Z Angle
Enables/disables limit rotation around the X, Y or Z axis respectively.
Lower
Lower limit of rotation for X, Y or Z axis respectively.
Upper
Upper limit of rotation for X, Y or Z axis respectively.
Springs
X/Y/Z Axis
Enables/disables springs translation on X, Y or Z axis respectively.
Stiffness
Spring Stiffness of the translation on X, Y or Z axis respectively. Specifies how “bendy” the spring is.
Damping
Spring Damping of the translation on X, Y or Z axis respectively. Amount of damping the spring has.
X/Y/Z Angle
Enables/disables springs rotation around the X, Y or Z axis respectively.
Stiffness
Spring Stiffness of the rotation around the X, Y or Z axis respectively. Specifies how “bendy” the spring is.
Damping
Spring Damping of the rotation around the X, Y or Z axis respectively. Amount of damping the spring has.
Motor

Panel: Physics ‣ Rigid Body Constraint
Type: Motor

Options available to a Motor constraint.
The motor constraint causes translation and/or rotation between two entities. It can drive two objects apart or together. It can drive simple rotation, or rotation and translation (although it will not be constrained like a screw since the translation can be blocked by other physics without preventing rotation).
The rotation axis is the X axis of the object hosting the constraint. This is in contrast with the Hinge which uses the Z axis. Since the Motor is vulnerable to confusing perturbations without a matching Hinge constraint, special care must be taken to align the axes. Without proper alignment, the motor will appear to have no effect (because the hinge is preventing the motion of the motor).
Options
Linear motor/Angular motor
Enable
Enable linear or angular motor respectively.
Target Velocity
Target linear or angular motor velocity respectively.
Max Impulse
Maximum linear or angular motor impulse respectively.


text:
Texture shows up with bg
I have a metal pyramid which I'm trying to make slightly covered with sand dust.
But I don't need it everywhere, so I decided to use a mask. I've never used masks before.
I'm using a texture for this dust as shown in the video (https://www.youtube.com/watch?v=ZmrCoGj9m2Y) BUT:
I have base metal material with normal displacement from a noise texture,
I have a dust img,
I have a mask.
When everything is set up and I paint the texture I also paint black background. In the video he has clean dust only show up on the model. He has nodes to make it appear only in sertain places (I use paint for that) but he doesn't have anything that makes it show dust without black bg
So how do I make it so when I paint only dust shows up and between it is my base metal material and not black bg of the texture?

Your node setup is basically correct, however, I think the "Black background" that you are seeing is because the nodes that define your dust are a mix between a diffuse shader and... nothing!
I will call the mix shader node on the left of the image the "first mix shader node", and the mix shader node on the right of the image the "second mix shader node".
So you are successfully mixing between the nodes that make up your base metal (second slot, on the second mix shader node) and the nodes that make up your dust (first slot, on the second mix shader node). But your dust is itself a mix between an Orange colour and no shader at all (which shows on the render as blackness). So your dust is coming out as orange mixed with black.
To fix - plug another diffuse shader into the second socket on the first mix shader node. Give it a slightly different orange colour. You should get results more like what you wanted.

So what you suggested worked
But that's not what I'm looking for
I now have Dark Brown "particles" of dust (you could see the on my screenshots) and Light Brown space between (I added a Diffuse shader as you suggested, of light brown colour)
But can I make it have no colour instead? so that we see "particles" of dust but no black or light brown inbetween but rather our shiny metal of the pyramid, so that we have an effect of dust on the model?
Is that possible?
The guy's render looks like he has exactly that and I can't get my head around it.

Yeah, there are lots of options. One option - you could just have a single shader for your dust material. Delete the first mix shader node, plug the dust.png texture node into the diffuse shader colour input, and then plug that into the second (and now only) mix shader node. Another option - keep your two tone dust material like you have now, and use a colour ramp node after the dust.png texture to push the black/white value up to a level that you are happy with. Bit hard to describe on here.


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Non-color data (and other) option missing
In Image Texture node I don't have any other options but sRGB and Linear.
How do I enable the Non-Color Data option in the dropdown menu?
I followed the tutorial (https://www.youtube.com/watch?v=W1px5mPdN4s) and the guy has it, whilst I don't. Switching to cycles did not help. I use Eevee btw.
Thank you, cheers

save your texture first!

What do you mean? I import it with image texture node, it's already on my computer

What kind of image texture are you using? Png, jpg etc.

jpg and tif. One node is a gloss map another one is normal, jpg and tif.
The guy in the tutorial also has jpg and tif files.

Looks like this option now shows up (at least in 2.83) after you open the image, under the "Color Space" dropdown:

I had the same problem and I searched a lot for a solution, I had a laptop that appear the all options, but on a PC it does not appear after a long search,
I found that downloading the blender from the official website does not have options, but I tried to download it from the Microsoft Store and it solved the problem, I hope the solution works for you


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Grease Pencil animation rendering only the background
I need to render an animation where the PNG files from the rendering will be saved. I'm using the demo file that is provided by Blender (https://download.blender.org/demo/test/ForYou.blend) - Grease Pencil Automation (ForYou.blend).
The problem is that when i'm running the animation rendering it creates the PNG files with the background only and the animation objects are not captured (same goes to a case where i create video file).
Any help will be really appreciated. Thank you

In order to render a grease pencil animation, you have to use OpenGL render.  Using the blend file that you provided, if you open it, up there are two views,
directly under the view that you want to render there is a plus

If you click that and then scroll to the right by dragging the middle mouse over the bottom section(the panel menu) you will see the OpenGL render button.

The one on the left renders the current frame and the one on the right renders the animation.  Just make sure that you deselect everything before you render as it is just rendering the viewport at a higher resolution.

Thanks for the quick response. Yes, i've already tried it and it works. Just wanted to understand if the inability to render the active scene (not the OpenGL way) is the limitation of this specific animation?

I'm not an expert but as far as I'm aware thats the only way grease pencil animations can be rendered

Thanks Ben. Will have to find some other animation then :)

Blender offers demo files here that can be used as benchmarks https://www.blender.org/download/demo-files/.  They have the splash screen ones, some cycles tests, and even some real-time ones.


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How to Extrude so That Extruded Face Isn't Parallel
I just had a quick quick question.  So in the image, you can see that when I extrude from an edge loop, the extruded edge that comes out of it is always parallel to the original edge loop that I extruded from.  How do I extrude so that the angle of the extruded edge loop isn't parallel to the original ie) it follows the door.  I know there is a way of doing this without creating curves and beveling.  Any thoughts?

Do you mean something like this?

With your faces selected, hit SPACE and find: 'Extrude Region and Shrink/Fatten'

You can't extrude too far in or you will have to clean the top up a bit.
You can, however, go about this backwards, too, using inset.
Model the inner radius first.

Extrude below the floor so inset doesn't mess with the lower end of your mesh.

Select the front and hit I

After that, repair the damage.

This is a nice option to know about but it does not, in my experience, do a reliable inset/outset . .. occasionally it looks right, often it does not.  It all depends on what you're looking for I guess.

Some topology doesn't like that tool, true. But I built an arch like the one in the picture and it behaved, so I thought it belongs in here.

Absolutely, it does belong here, it is a good solution in certain cases!

Thanks for the answers, I ended up manually going in and rotating each loop to go around but those other answers are really useful as well:)

To clarify a bit, since the answer was edited subsequent to my comment: shrink/fatten does work fairly reliably on faces.  The modified answer shows how to use it in this fashion.  However, it does not work reliably on edges, which is what the question concerned.  The Offset Edges plugin works on edges without having to locate or create faces with normals pointing in the right direction.

Sorry, I have the nasty habit of iterating my answers. I admit that I didn't think of it as an edge problem because the intended result was probably a watertight mesh again.

I am a newly-converted fan of the Offset Edges plugin.  It does exactly what you're describing (I think, based on your description).
https://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Modeling/offset_edges
Edit: it does this type of thing:


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Tried Everything, Can't Generate a Correct Normal Map
I have been working on making a normal map where I project it from a high poly to a low poly mesh.  I have tried cages, adjusting margins, adjusting ray distances, basically everything and I'm still stumped.  The best I can get my normal map to come out to is attached below.  What're your guys' thoughts?

What were you baking from? How does highpoly look like? Does it have faces which are beveled and oriented not at 90 degrees to its flat surface? Margin setting is not something that will have any serious impact, so it can be left on defaults

Is the low poly and high poly object in the same or almost the same location ? If you change the location then the normal maps are going to be projected in an unwanted way.

Sorry for the late reply, been at work.  So if you look in the picture, you can actually see both the low poly and the high poly @MrZak.  The low poly is gray for the material that I had to add (to put the normal map image onto the image texture node) and the high poly is that tan object you see.  The faces aren't beveled and are parallel with the surface.  But beveling can screw things up?  Also, I am baking from the high poly to the low poly mesh

@Retrax, the two meshes are indeed at the same location, same origin spot, everything is applied, etc.

Now I see both objects are there in place however this doesn't allow to see geometry of the highpoly. This is important since if highpoly doesn't have some curvature on its corners there won't be any normal map effect - it doesn't catch 90 degree corners. See https://blender.stackexchange.com/questions/29268/weak-normal-map-bake for example. Bevel can make it worse, can make better, depends on geometry mostly, but it isn't the only way to model highpoly

Ah that makes a lot more sense.  I added a subdivision surface modifier and it did the trick.  Thanks so much for the help man! @MrZak


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What is Node Wrangler Used For?
Can someone explain to me the basic concepts behind why one would want to use the Node Wrangler add-on?  Thanks for the time!

http://gregzaal.github.io/node-wrangler/ The addon makes working with nodes a lot faster and easier.

See https://blender.stackexchange.com/questions/1691/way-of-seeing-data-as-image-anywhere-in-a-cycles-nodes-setup

Thanks @MrZak!  I actually looked at that post and didn't read all the way down where the answer was.  My bad


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Problem Trying to Bake a Normal Map To Access Blue Values of the Normal Map
I am trying to bake a normal map for this object but it isn't working.  I am basically trying to add dust to an object by just accessing the blue values (the values that are upward facing on the normal map so that I can add dust just to the top of the model) through a separate RGB node once I have a normal map as shown in this picture:

I am not trying bake from high poly, to low poly, rather just trying to create a normal map for the object itself.  I included the UV unwrap I did and the image that comes out after I bake is completely blue which would suggest that my model is at the same angle as the normal map that's trying to be created but that's impossible because of how spherical my object is.  Any thoughts?
Thanks!

You don't need a normal map to access the normal vector of the face. Is there a reason why you would like to bake it?

So I want to access all of the upward facing vectors. I thought I had to do a normal map to do it because when I tried to it without a normal map, I couldn’t get just the upward values, I got the normals for example coming on the bottom of the arm and that’s not where you would expect to see dust if that makes sense? @Carlo

Did you check the CLAMP option in the color mix node as shown in the tutorial? That should prevent negative Z values from being take into account.

I did yes @Carlo


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How does the Vertex Weight Mix Modifier Work Internally
I've gone through all of the documentation and been fiddling around with this modifier for an hour.  Can someone tell me how it works?  What is it actually doing?  My understanding right now is that it mixes different weights (which you set by vertex groups) and I understand all of the blend modes and what not).  Essentially, I understand a lot of what it's doing but I can't wrap my head around this problem.  In the vertex groups you set a weight for your vertex group and then in this modifier you have an A and a B group and you set default weights for the A group and the B group.  What is the interaction between these different weight settings?  How does it work together?  Also, how would you use a texture map on this (I looked up the blender post for this at Remove vertices based on texture but couldn't figure it out).
Thanks so much for the help!

Have a slow read through the manual page on the vertex weight mix modifier, it has an example at the end to help explain it.
The points I think are most relevant -

Vertex Group A
      The vertex group to affect.
Default Weight A
      The default weight to assign to all vertices not in the given vertex group.
Vertex Group B
      The second vertex group to mix into the affected one. Leave it empty if you only want to mix in a simple value.
Default Weight B
      The default weight to assign to all vertices not in the given second vertex group.
Mix Set
      Choose which vertices will be affected.
All vertices
          Affects all vertices, disregarding the vertex groups content.
Vertices from group A
          Affects only vertices belonging to the affected vertex group.
Vertices from group B
          Affects only vertices belonging to the second vertex group.
Vertices from one group
          Affects only vertices belonging to at least one of the vertex groups.
Vertices from both groups
          Affects only vertices belonging to both vertex groups.
Texture Mask
      An additional texture, the values of which will be multiplied with the global influence value for each vertex.

So Vertex Group A is the group that gets the result, you use this in modifiers after the mix.
The mix mode defines how the two values are mixed, while the set decides which vertices get the weight.
The texture mask can then limit the result to certain areas of the mesh.

Thanks for the response @sambler!  So the texture mask that you use basically applies the black and white values for selecting vertices on group A only.  Is that correct?  Also, to do this, would you have to UV unwrap the object from which you are selecting vertices?  Lastly, were you saying that "Vertex Group A" will then show up as its own vertex group when I use it in other modifiers or would I have to specify it as an attribute?  Thanks man!

GroupA gets the calculated vertex weight, if you have a wave modifier after the weight mix and set its vertgroup to GroupA then the calculated vertex weight will affect the wave. The mix set defines which vertices get the calculated weight assigned to them. UV's have no effect on the vertex weights, they may be used to affect the texture used. In the texture black=0.0 white=1.0, the calculated weights are multiplied by this value, so black parts of the texture mean no weight and white parts mean the full calculated weight.

Thanks again for the response @sambler!  You fully answered two of my questions, and for the final question, I didn't elaborate so that was my fault.  So say I add a procedural textural ie) noise for the sake of clarity and I want to use that texture to be able to get a weight of 1 where the noise texture is white and 0 where it's black on a cube mesh.  Blender will basically use default texture coordinate mapping of the noise texture to be able to put those weights on there yeah?  And then for example if I wanted to get a weight based on an AO map then I would have to UV unwrap yeah?

If you have baked an AO map then you will want to use uv's for that image texture. For procedural textures, you can do either. For any texture you can choose a mapping type of generated, object, uv, world, camera...

Awesome that makes sense.  Thanks for the help!


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What are the practical applications of the voxel data texture?
I have looked quite a bit at the capabilities of the voxel data texture.  I understand that it is "volume pixels" where it gets its name from.  It looks like they can use it some programs to take slices of images and reconstruct 3D models out of it like reconstructing MRI and CRT scans which is super cool.  It's seems like this could be such a powerful thing in terms of getting really cool effects because you can access the data of these "volume pixels" and do some really cool things with it.  I know it's used for smoke simulations.  Could you use it to do cool things with point density stuff like cloud creation and whatnot?  Based on my limited knowledge on it, it seems like there aren't a lot of practical effects you can use with this or it would be getting used more often.  What're your guys' thoughts?


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Shrinkwrap Modifier Doesn't Conform After Having Geometry Follow Profile
I'm trying to retopologize a flower stem that I sculpted.  I am applying a shrinkwrap modifier to a circle where I close follow the geometry and then as I understand it, the shrinkwrap modifier should conform to the original mesh.  It seems to be conforming decently but it is super blocky and isn't smooth.  I thought it might have to do with the fact that the sculpting underneath isn't smooth enough.  What're your guys thoughts?  I'd be curious to understand what is going on "under the hood" with the modifier and triangles (and their normals) from a mesh sculpt.  Here are the images, the first one shows the blockiness of the wrap and the 2nd one shows my sculpt:

This is expected.  You cannot perfectly represent a high poly model with a low poly one, or else we wouldn't have any high poly models.  Your low poly retop will not match your stem exactly.  Make sure you have smooth shading and try to represent the edge flow of your model, retopo takes practice as much as anything else.

@Nathan That makes sense.  Thanks for the help man!

Change the order of your modifiers.  Shrink Wrap first then SubSurf. See which one you like better.

The most efficient solution to problems like this, for me, involves both the subsurface modifier and then, after it, the decimate modifier. The problem comes from the lack of relative equivalence in vertex count for your two models, the shrinkwrapper and the shrinkwrappee.
You can apply a basic Subdivision Surface modifier to the wrapper, typically set to Simple, with a count high enough to remove the seams. (Naturally, make sure you set your wrapping mesh to "Shade Smooth" first.) This has been discussed before, but is very inefficient on its own for storage and crippling if you're building for something like a game...
So, once it is high enough, you're likely to have more vertices than you actually need. You can use a Decimate modifier to drop them to a low percentage of what they were, using the "Collapse" setting. You'll have an edge count visible in the modifier, get it as low as you're comfortable with. Generally speaking, the lower the edge count, the better; but after you hit a certain point you will start noticing artifacts.
Depending on the mesh, I can usually bring it down to around 0.25. Collapse mode removes the least significant edges first for the overall flow of the mesh; so it's reasonably intelligent about what gets to be kept, and what it can ditch, given its parameters. (You will be amazed just how much unnecessary baggage your model can be carrying after a SubSurf.)
The best thing about these modifiers is that the additional vertices are not stored in the model file, to my understanding; they're created at run-time. For a game, you will want to apply the two when you're content with them, if it isn't done automatically. Otherwise, if you have something else deforming it, like a hook or an armature modifier, which works before the subsurf and decimate modifiers, it will continue to work; though you may sometimes have to wait on modifier processing for a second or two.


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Constructing a Flower from Multiple Parts Texture Map
Anybody know the best way to make a flower out of this texture?  The texture has everything I need in terms of an alpha mask, glossiness, normal etc.  How would I construct the mesh from this?  Could I use one subdivided plane (to put all of the textures onto) and then cut out separate parts of the plane and retopolize the parts?  Or would I make multiple planes and then have their UV map align to a part of the image?  What're your guys' thoughts?

Perfect.  And then due to the fact that I have an alpha mask, I don't need to match the shape exactly.  Is that right? @cegaton


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Create a 3d model with python API using Postgis Polygon
I want to create a simple 3d structure using the coordinates of a GIS polygon(latitutes and longitudes of vertices).
For example a coordinates of a polygon would be like this:-
{"type":"Polygon","coordinates":[[[-121.332737,38.722023],[-121.332895,38.722023],[-121.332895,38.721977],[-121.332946,38.721977],[-121.332946,38.721881],[-121.332737,38.721881],[-121.332737,38.722023]]]}

I want to create a simple structure with blender API using this footprint as a base.

This script will generate a mesh object from the coordinates provided in this specific structure.

It will also add edges (assumes the vertices are in order), and one ngon face from all verts.
Note that this mesh is huge and to see it with the default view settings, you need to either be in orthographic mode or set you view clipping to a much higher value.
import bpy, json, bmesh

data_string = '{"type":"Polygon","coordinates":[[[-121.332737,38.722023],[-121.332895,38.722023],[-121.332895,38.721977],[-121.332946,38.721977],[-121.332946,38.721881],[-121.332737,38.721881],[-121.332737,38.722023]]]}'

dataDict = json.loads( data_string )

coordinates = dataDict['coordinates'][0]

bm = bmesh.new()

# Generate vertices
for co in coordinates:
    # Add new vertex at the provided coordiante with z=0
    bm.verts.new( co + [0] )

# Generate edges
bm.verts.ensure_lookup_table()
for i in range(len( bm.verts )):
    if i == 0:
        bm.edges.new([ bm.verts[i], bm.verts[-1] ])
    else:
        bm.edges.new([ bm.verts[i], bm.verts[i-1] ])

# Generate one ngon face
bm.faces.new(bm.verts)

# Generate a mesh and transfer data from bmesh object
m = bpy.data.meshes.new('GIS')
bm.to_mesh(m)

# Create a new mesh object and link to scene
o = bpy.data.objects.new('GIS', m)

bpy.context.scene.objects.link(o)

Hey, thanks for the answer. But after running the script the mesh is not appearing. Can't even see in orthographic view. Am I missing something?

After you go to orhtographic view, press Home on your keyboard to see everything, and all will be revealed (dramatic tone not intended lol)

I feel stupid now, but I'm still not seeing it. Zoomed out as much as I could. It's running without any errors. But I just can't see anything. Tried exporting .dae and .obj files too. But even they appear to be empty. I'm on mac by the way (irrelevant, but still maybe helpful).

Did you select the object? you can do it from the outliner if you can't see it at all

Recommend subtracting first coordinate from all vert coordinates, which  will put one coord of area of interest at global origin.  Secondly remember that lat, long  coordinates are spherical (the earth is an ellipsoid) and some georef / datum should be used when converting, as method above is basically a simple equirectangular projection, which will be way off as latitudes increase.  Lastly is there a need to create edges?

With help of @TLousky's answer and @batFINGER's comment, finally this worked for me.
import bpy, json, bmesh
from math import *
from mathutils import Vector

data_string = '{"type":"Polygon","coordinates":[[[-121.332737,38.722023],[-121.332895,38.722023],[-121.332895,38.721977],[-121.332946,38.721977],[-121.332946,38.721881],[-121.332737,38.721881],[-121.332737,38.722023]]]}'

dataDict = json.loads( data_string )

coordinates = dataDict['coordinates'][0]

x_factor = coordinates[0][0]
y_factor = coordinates[0][1]

verts = tuple([((x[0] - x_factor)*10000, (x[1] - y_factor)*10000) for x in coordinates])

bm = bmesh.new()

bm = bmesh.new()
for v in verts:
    bm.verts.new((v[0], v[1], 0))

# Generate one ngon face
bottom = bm.faces.new(bm.verts)

top = bmesh.ops.extrude_face_region(bm, geom=[bottom])

bmesh.ops.translate(bm, vec=Vector((0,0,1)), verts=[v for v in top["geom"] if isinstance(v,bmesh.types.BMVert)])

bm.normal_update()

# Generate a mesh and transfer data from bmesh object
m = bpy.data.meshes.new('GIS')

bm.to_mesh(m)

# Create a new mesh object and link to scene
o = bpy.data.objects.new('GIS', m)

bpy.context.scene.objects.link(o)

Good one. Generally GIS data will give us coordinates that walk around a face, in which case bm.faces.new(...) works. Incase they are messed up could use contextual_create eg ret = bmesh.ops.contextual_create(bm, geom=bm.verts) new face is ret['faces']  ... bmesh.ops.solidify(...) is another way to add thickness.


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Unable to individually give material to bark and leaves
I am using blender 2.79, and in using the sapling gen addon, I am unable to add different materials to both bark and leaves.I'm a total beginner, so it might be an error on my part.Please tell me what is needed.

The Sapling Gen Addon should create two separate objects for the tree and the leaves if you select the leaves and add a material with whatever color you want it should assign that material to the leaves only.


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Attribute node for Vertex color texturing problem
I would like to use vertex color information for texturing. I found some description on the web but there is something what I can't figure out. If I use a color at 0.5 value, the FAC value through separate RGB node looks like not 0.5 result. What am I missing?

If I disconnect node from FAC at mix shader and set the value manually to 0,5 I get the result I'm looking for.

I put a 'Gamma' node between the 'Attribute', and 'Separate RGB' with a Gamma setting of (1/2.2), that is to say,  (0.45454....) and it seemed to correct the 'Fac' in the mix. A proper answer would explain which color spaces get used down this pipeline, and justify the setting, so this is just a comment.

I found an answer from a much more reliable source, here

The gamma node really helps, Thank you! The background of color spaces is "chinese" for me at first look, but maybe later I will learn about this.

It is confusing, because which spaces are used by which bits of the system is not always well documented.


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Mantaflow simulations causing strange diamond artefacts
I've create a fluid simulation with mantaflow and am rendering the FLIP particles themselves (no mesh). The simulation looks great (with a resolution of 96) but when it becomes quite turbulent there are strange "diamond shaped" artefacts appearing and disappearing sporadically.
You can see it here:

And it's very noticeable in video (in the center where the two fluids meet):

Is there a way to get rid or reduce these artefacts?

have you tried changing the resolution?

try having resolution values like 32, 64, 128,  or 256

@Jonas I tried different resolutions yes.

@Rakeshchoudhary Mh, I had 96 as a resolution. You think that this could be the issue?

Please attach blend to your Q via https://blend-exchange.giantcowfilms.com Thank you

I tried with 128 but the diamonds were just a bit smaller.

Any problem post the blend I asked for? A you can see your red sim in fine, means yellow setup produce it. We don't know what whole setup is used, means - it is hard to help when we don't know what setup you use :)

@vklidu the blender file is really big, because it contains high-res models and the simulation data is ~5GB. The Red part generates the exact same diamond artefacts, it's just not as visible. I have 6 simulations in total, with the exact same problem.

@enyo I haven't seen this artefact before, and from silent here maybe also others don't know how to reproduce these diamonds, means - they can't look for different setup if works or not. (also it can be something that just sim works like this and there is not a fix at the moment). Also what blender version was used? BTW I don't think you have to share baked and meshed sim. Keep just domain and flow object (or other elements used in sim), or append them into a new blend and share, they should be just a few kB.


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Why is blender saying some of my scenes have no user
Blender started "randomly" deleting some of my scenes and when I checked, it was because it said there are no users. I figured out how to add a fake user now (via the "Orphan Data" Outliner) but I'm still unsure why this is necessary.
Why would a scene require a user, and how can I make sure this doesn't happen in the future?
I also haven't found any pattern to which scenes are marked as having no users.

Related https://blender.stackexchange.com/questions/176758/how-do-i-fix-a-scene-with-zero-users

Exactly my issue.


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Strip length does not update with sequence length
When I add a Sequence as a Strip in the Sequencer, and then increase the length of my sequence, the strip does not take into account the new length and always stops. Is there a way to update the strip so it contains the whole length of the sequence?
Here you can see that my strip is ending at the playhead

After adding the sequence again, it works as expected.

I've made a bug report here: https://developer.blender.org/T76222
As an alternative, the Hold offset values can be changed in the Time sidebar panel(the values are really odd, but it is possible to make it longer)

I'm sorry, I can't code a solution for you, but do you have additional questions?

Thanks @tintwotin! I wasn't able to get it to work with a hold offset, but I'll try. A fix for that would obviously be best :)