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How can I improve the realism of my pencil texture lines in freestyle?
I'm using a charcoal image texture to make my cycles freestyle lines look as though they were drawn by hand with a pencil. My inspiration (and the source of the charcoal image texture) was the teapot file linked on this page https://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.71/Freestyle

This is the charcoal image texture:

The concept works okay when you use multiple rounds to go over the same area a few times, but when I try to draw a single line it looks a bit crappy, with the repetitive nature of the texture very apparent.
Multiple rounds:

Single round (which is what I'm after, ideally):

I'm wondering if there's a secret to getting more realistic single stroke pencil texture lines in freestyle? Do I need a better texture? A more random way of having it repeat? Or something else? Hopefully things have moved on in the three years since that texture was created and used in the teapot model.
I've attached simple test file here:

If for some reason the charcoal texture doesn't appear in the file, you can grab it from my post.
Thanks!
p.s. I'm aware of this question How can I use pencil style strokes in frestyle? but those answers simply point me towards the files I've already referenced.
Update May 29th 2017: Spurred on by Mr Zak's answer below I made another version with multiple rounds of lines and a little randomness. While I realize I can get close to what I want with this method (as the layering of the textures creates more randomness), I'm still interested to know if there's a way to improve the realism of the texture on a single stroke. But in the meantime here's what I achieved with multiple rounds and the settings I used. Perhaps it will prove useful to someone else.
Finished image:

Close up of one line:

Settings:

Update 2 May 29th 2017: Since someone asked, the project I'm working on is a series of line-based maps that I'm hoping to render as though they were drawn either in pencil or in pen. I'm still fiddling around trying to work out the final look and feel of them, but knowing if I can achieve the pencil or pen look is a part of that.
Here's an example of where I am so far:

As you can see the lines representing the terrain already have a good deal of randomness and wiggle in them, so that's why I was concentrating mostly on the texture of the stroke. It might be that the lines end up being too small to even register a texture, but as this is an ongoing discovery I wanted to understand the full extent of my options.

Thanks cegaton. I did try that before uploading the blend file, and thought it had worked, but I guess I got it wrong somehow. Also, thanks so much for adding the bounty! That was super kind of you :)

Maybe still related - https://blender.stackexchange.com/questions/31225/how-to-do-custom-freestyle-brush-shape-in-blender-2-74

According to the wiki article Textured Strokes the Use Tips option is available when Along Strokes mapping is used:

Along Strokes Means that the texture will be drawn along the stroke length, making it possible to mimick pencil or brush marks.

However by default it won't really make any much difference:

The option depends on spacing between strokes mapped to the geometry:

Along Stroke mapping depends by the LineStyle spacing parameter that can be found in the linestyle settings. It sets how much the texture will be stretched along the stroke length. Higher spacing means less tiling.

It can be found in the same place where strokes are set up to use texture, Render Layers tab > Freestyle Linestyle rollout > Texture panel:

With that texture rendered strokes become more smeared:

Spacing was set to 5
The effect however is still a bit off as its thickness is not varying and the stamp still is present.
From here on settings from the teapot file were used as reference as well
To correct that don't use thickness of 20; in fact less than 10 will be enough. For convincing and effective results better to let it draw with thin line and repeat it 2 or more times; that will simulate effect of graphite or a pencil strokes more nicely.
This is the result wil Stroke effect decreaed to 6:

Now some repeating pencil strokes would add a bit of "realism" to the image. With Repeat set to 3 it will be already more or less good. But to add even more to that in the Geometry panel add Spatial Noise modifier.

What the modifier does is it varies strokes created by the Repeat option. Amplitude option will increase or decrease how far away the repeated lines are from original; Scale adjusts the scale of repeated detail (if it was at 15 you'd get step-like corners around the line).
Smeared chalk like effect can be created with Along Stroke modifier added to the Thickness panel. According to the manual it applies gradient along each stroke while substituting original values of the line. To make lines more fat and smeared Use Tips option can also be unchecked (in this case):

The partially transparent effect from the teapot scene is created with adding Along Stroke modifier in the Alpha panel, but for some reason in Cycles it isn't visible (teapot scene is in Internal). Even setting Thickness to 0 doesn't really change anything, which is quite unexpected. It looks like in Cycles the freestyle won't calculate and hence use alpha of the charcoal texture. If making that in Internal effect shows up immediately:

It's hard to say if this means for you that Freestyle went ahead since that time but anyway the resulting effect of the freestyle strokes can be changed quite drastically by editing options and adding modifiers.

If going with only one round of the stroke (and hence only one stroke drawn on the objects) you will need to alter it as much as possible in order to get varying style. You can use several line styles as already mentioned by @TK or you can go with more modifiers for one line style.
I will use modifiers for Thickness panel mostly but possibilities are nearly endless as many of them have also additional modes of stroke overlaying which changes end result quite noticeable.
Note:

there aren't any modifiers on the line style for this one; none of the results used from the several rounds above.
in all the results here Face Smoothness in the Render Layers tab > Freestyle rollout is used for using smooth shading of the mesh.
It also means that shading of the meshes should be set to smooth as well.
in all the results here Alpha Fac in the Line Style Output node in the line style setup is set to 0.5. This allows Cycles to overlay alpha of the texture and use it along with the base color. For some reason it also fixes usage of the modifiers in the Alpha panel. None of these is needed in Blender Internal.

Using stroke thickness (Freestyle Line Style > Thickness) at 3 and Spacing at 1 the result is thin drawing:

To increase the variation add Along Stroke modifier to the thickness of the stroke. It will apply new values for thickness based on the progression type and blending mode choosed; from the manual:

The Along Stroke modifier alters the base thickness with a new one from either a linear progression or a custom curve, mapped along each stroke’s length. In other words, it applies the selected progression along each stroke.

To mimic caligraphic changing of the line thickness which depends on the stroke angle add Caligraphy modifier. Its  Orientation property will simullate orientaition of the virtual pen drawing on the paper - the more it's aligned with the vertical axis the more horizontal strokes will be fat and vertical - thin. Default values of 60 are quite good as well.

Also it's possible to add some noise to the stroke in general; Noise modifier will be the last in the Thickness panel.

To simulate transparency of the strokes modifiers in the Alpha panel are added. In this example Along Stroke modifier is used.

Note also that most of the modifiers can be set to another blending modes thus altering their final result which allows even more different things to try.

As a probably useful disclaimer the reason of existence of this answer wasn't just the bounty.

Thanks so much for putting all that effort in, Mr Zak! It seems like my hope that there's something simple that can be done to make a single stroke texture look more randomly real isn't possible. I also found that multiple rounds of strokes helped cover up and randomize the texture a bit more, but I was hoping to be able to get away with just the one line. If you don't mind I'll leave this an unanswered for now in case anyone else has something to add. Thanks again!

@Dunstan that's totally ok to leave it unaccepted, I don't add answers for that.. What kind of strokes are you aiming for and what requirements do you have? I suggest including that in the question. If usigng 1 round you can easily get more or less good defined stroke by adding e.g. Bezier Curve modifier to Geometry and 3D Curvature to Thickness. It really depends on desired result and amount of time you're ready to spend.

Thanks again for all your efforts on this. I really appreciate someone double-checking my work and adding in extra ideas. I've added an example of the kind of thing I'm working towards using this technique in. I think that unless someone comes along with a crazy idea out of the blue, your kind suggestions are is as close as we'll get. Many thanks again.

COOL!!! I hope I can do this in 2.81 version.

How about using 3 line sets instead 1 doing 3 sketchy repeats?  For each of the 3 linesets you can specify almost the same line style settings but with minor differences that create desired randomness.  Here's the result of my attempt based on the provided .blend file:

And here's a screen capture of the line style settings:

Summary of changes:

The 3 linesets and corresponding line styles are respectively named Base, Overlap #1 and #2 as shown in the screen capture.
In the latter two line styles, the Tip Remover modifier is used to shorten the lines for 2 and 4 unit lengths so that the charcoal texture starts with different offsets, making texture repeats less visible.
In addition, the Spacing Along Stroke in the Texture pane is set to different values in the 3 line styles (here 0.1, 0.2 and 0.3, respectively) to give texture repeats different stretching effects.
Since the 3 drawn lines overlap, the transparency of the 3 line styles are set to 0.5, while the Alpha Fac of the Line Style Output node is also set to 0.5, so as to make the textured strokes not too dense.

I hope this helps you better deal with uniform texture repeats.

Ah, very clever, thank you!. I feel a bit silly for not having thought of that :)

Most of the options are already well covered by Mr Zak and T.K.'s answers, but here's some more methods. The big issue with the textured stroke is that it basically gives you a dotted line of boxes that each hold the texture. But there can be splits or overlaps that cause problems, or gaps where strokes break.
Compositor
The most simple solution if you only want a single stroke is to use the freestyle lines as a mask to overlay a stack of textures in the compositor. This can be instead of using textures stroke, or in addition to it. For this, you will want a clean line set with thickness and alpha modifiers as Mr Zak describes, and then you will need a high frequency charcoal texture to overlay the whole image based on it. There are lots of potential ways to overlay it. Mixing several different textures together, and then varying them with cloud textures or something similar will probably get best results.
To help get your lines nice and clean, people usually put them through a blur, and then multiply the original lines on top of the blurred lines to feather the edges. They can also be put through filters like laplace and kirsch and then mixed back together to get a bit more variation.
Multiple Meshes and Line Catchers
While it probably isn't what you'll be after in this case, it is also viable to add more meshes or mesh pieces to catch lines. So instead of more rounds, or more linesets, you can have more meshes. This could be a simple curve in an area that you know needs to get a line, all the way up to an instanced version of the mesh on a separate layer that has a different amount of subsurf, smooth, or decimate.
A slightly different version of the mesh will mean you get a different chaining pattern. If you use multiple render layers off different versions of the mesh and combine then in the compositor, you can have quite a bit of control. (I doubt that will suit this particular project, but it may help others looking at this question.)

That's a super helpful extra solution. Thank you so much!

Under "Texture Mask" tab, in UV Paint Mode, there is an option button called "Random", which rotates the brush randomly in strokes. You can set the max random rotation offset by changing the "360" degrees to whatever angel you want for strokes.

Please explain how this affects the cycles freestyle lines of the question.


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Programmatically selecting every nth edge loop in a mesh?
I need a programatic way to select every nth edge loop in a mesh, in a certain plane. (In the examples below I've shown a mesh with only 12 x/y subdivisions, but in practice my meshes have hundreds of divisions – far too many to select by hand.)

Is there a common solution for this? Or a script I could look at and learn from? I've tried using python – https://docs.blender.org/api/blender_python_api_2_67_1/bpy.ops.mesh.html –  for this, but I'm not familiar enough with things to get any practical results. Would love to learn, though.
FWIW I've tried selecting all edge loops in a certain plane, and then using "checker deselect" to achieve the same result, but that doesn't do what I want.
Thanks very much,
Dunstan

are your meshes always grids like this?

They are, yes. The only difference between them is the number of subdivisions. (And thanks for helping!)

Following instructions from the related answer you can select them with UI as well.

Select one edge perpendicular to the resulting edge loops. Run Edge Ring from the Edges menu (Ctrl+E) or press Ctrl+Alt while selecting the edge to select ring of edges based on the first selected edge.

Run Checker Deselect.
That's where you will adjust the selection pattern according to which you'd like to select (skip two loops, select the 3-rd, skip one, select the other one etc). The only difference is that you act on only one edge corresponding to each loop.

Finally execute Edge Loops from the Select menu in the 3D Viewport header or press Ctrl+E to spread selection on the adjacent edge loops.

Well damnit, I can't believe that. I initially went through all those steps, but the very last part escaped me and I assumed I couldn't use that tool. Yes, that does seem to be a more practical solution. Thank you, WKG.

By assuming your grid will be parallel to the x-y axis and not rotated, I came up with this idea. It works fine for me and hope this helps.
import bpy, bmesh

# These are the parts that you can change, inputs
step_size =            5
first_selected_loop =   0
x_or_y_parallel =      "x"

# Switching to EDIT mode to read mesh data
bpy.ops.object.mode_set(mode = 'EDIT')
bpy.ops.mesh.select_all(action='DESELECT')

# Program will get the zeroth index or first index of vertices
# (that is x or y coordintes) according to your choice
if x_or_y_parallel   == "x":
    x_y_index = 0
elif x_or_y_parallel == "y":
    x_y_index = 1

# Getting the mesh data
obj = bpy.context.scene.objects.active
bm  = bmesh.new()
bm  = bmesh.from_edit_mesh(obj.data)

# Getting all line coordinates that is parallel to selected axis

# I am assuming we don't know how many lines we got in x or y axis
line_x_or_y_cords = []
for vert in bm.verts:
    if vert.co[1-x_y_index] not in line_x_or_y_cords:
        line_x_or_y_cords += [vert.co[1-x_y_index]]

# I am sorting the line coordinates and
# eliminating unwanted coordinates (we need only the lines that are on
# step size by starting first_selected_loop)
line_x_or_y_cords.sort()
line_x_or_y_cords = line_x_or_y_cords[first_selected_loop::step_size]

# if the edge is not selected yet , if 2 vertex of that edge is
#parallel to our expected axis and if one of its vertex is in our list
# (that is arranged above) select that edge and do select loop
#operation
for edge in bm.edges:
    if edge.select == False and (edge.verts[0].co[1-x_y_index] - edge.verts[1].co[1-x_y_index] == 0) and  edge.verts[0].co[1-x_y_index] in line_x_or_y_cords:
        edge.select = True
        bpy.ops.mesh.loop_multi_select(ring=False)
bm.free()

Hooray! Thanks so much, Alperen! That script runs perfectly when I put it in a txt file and click "Run Script", but cutting and pasting it into the console gives me a small error:
File "<blender_console>", line 5     bm.free()      ^ SyntaxError: invalid syntax
Any thoughts on why that is?

That's really going to help my project advance. Thank you again for putting so much effort into helping me :)

I'm glad that I could help:) I have blender 2.78a and I don't get any errors. You can delete bm = bmesh.new() and bm.free() lines if you wish, it still works:)

Also, sometimes blender just closes after I run the code and I don't know why:)

Ah yes, my blender closed a few times too after running it :) Perhaps there's something in there that freaks it out. Well thank you so much for going to the trouble of writing all that code for me. I see that there's another solution posted here that's probably more practical since it uses built in tools, but I really appreciate your answer too!

Thank you for your kindness too, I upvoted the answer you said since it seems much more simpler:)

@AlperenÜretmen.
The code you posted works nice though I have 1 request
Can it be modified with z Coord? to only select edges on specific height?
Please see this post
maybe you have better idea on how to solve my question
https://blender.stackexchange.com/questions/162456/select-edge-loop-of-mesh-using-python

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Cutting the face it create extra geometry
I have a simple object and i want to cut that object with the cylinder and im getting extra geometry. a file attached to know more my problem

its because the boolean operator works only on volumetric meshes.
say tube and cube, but not tube and plane. a plane is flat.
also sometimes it goes wrong because you think the shape is 3d but its not some flaw, resulting in a non watertight shape.
in your case you might apply a solidify modifier to the plane and then go on with what you did. (you need to apply it, not only add the modifier).
happy blending.

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How to vertex slide outwards?
How can I extrapolate a vertex/line along its tangent, as in the gif below?

do you mean to slide your vertex along the side outwards? There is a double G shortcut to activate sliding of the vertice on the edge, once you Alt whíle GG is active you will see that your vertice can slide outwards... is that what you wanted?

yes that is exactly what i wanted, thank you. can you add that as the solution?

Hopefully it will help even more people, I notice a lot that many people don't know about this

Pressing G twice will activate sliding of the vertex on the edge:

If you hold Alt while GG is active, you will see that yellow line is extended and you can slide outwards:
Edit: You can also press C instead of holding Alt to activate sliding outwards

Alternatively you can press C to toggle the line extension on or off. More friendly towards users with disabilities.

true, somehow I only use C with knife... don't know why

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Why duplication not follow path
Im making duplication along the path. I have a mesh and a curve path. Selecting the mesh and curve i press Ctrl+P and selected follow path. In Duplication i turn off speed. The mesh is not following the path in circular shape. Its twisted. I applied scale and rotation to both curve and mesh yet the result is twisted. Any suggestion or help.

dupli error file

I tried your file, and just after removing the parent in "object > relations" and selecting again "cube.004" in that listbox, the parent is better:

something didn't update correctly during some previous operation, maybe.
edit: ok, it is nearly the same even with the new file.
this time, after re-applying the parent as above, you need to clear its origin.

Have u done other settings other than that my result is different the mesh going away from the curve

no, just opened the file, and tried to reassign that parent object....I tried again now.

Sorry i have send the wrong file. I have attach the new file (dupli error)

ok, I updated the answer

Yes thanks i send the wrong file before so i was getting different result. This is perfect now.


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Why no lights enter the room
I have apply glass material and sun is in the position everything looks good but no lights enter the room. I have added hdr file and a lamp. Whats the reason what im missing to get light enter the room. All black inside the room and just the hdr image is seen from the window. In the red mark there is no light. And in green mark where the edge is coming from as there is no wall. And from the window the background look so artificial.

Related: http://blender.stackexchange.com/questions/2558/how-to-illuminate-the-darkness-inside-glass-objects-in-cycles and http://blender.stackexchange.com/questions/71570/why-is-there-no-light-passing-through-the-window

@PaulGonet thats my question in that and i did not get the answer i need why there is no light passing the room i have the glass material perfect still no light enter. plz download the file and go through and tell me where im going wrong thanks

If you need to add more information to a question, clarify that the provided answers do not work or that your question isn't a duplicate you should use the 'edit' button below your question to update it instead of asking the same question again.


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How to align duplication correct way
With the reference image attach. Im making the sandals and im the way to plug the diamonds in that. I have remove the center edge from the mesh. With the duplication im making the diamond to rotate around the curve. From side view it looks good but when i rotate and see the diamond going upper side and some diamond gone inside the mesh and only 1 diamond ring is visible. How correct align with the reference image the diamonds.

Related http://blender.stackexchange.com/questions/68923/torus-object-stretched-in-array-curve-modifier

@lemon may i know why i have to add a plane and empty is it necessary can you make it clear

I think the empty is not needed for you. About the plane: this is a way to avoid the diamonds to be deformed if they are directly curved. So as the diamond is dupliface of the plane, it is not deformed even if the curved plane array is deformed. But sometimes these deformations are not so much visible, so you can also curve an arrayed diamond directly (just try what is the best in your case)

@lemon after adding the plane and set fit curve there are no duplicate are performing i have attach the file above what im missing

Have you activated dupliface on the plane, after the parenting?

@lemon yes i have activated the plane

Could you upload the file again?

I have got the answer but i want to learn different methods also for future so i do prefer your answer also plz this is the file

I think you just missed to check 'faces' in the 'duplication' section of the plane's property panel (not visible in this new blend file as the parenting is not done). This is called 'dupliface' also (like you checked 'dupliframe' in the first blend file). Get it?... and before doing that, apply the scale on the plane (or the result will be very large)

@lemon with the reference video i have made that duplication its on frame not faces. What is difference between faces and frames Thanks https://www.youtube.com/watch?v=Rp88ckdLwVQ

Dupliframe is for objects that have no faces. And I suggested duplifaces for the plane you attempted to use yesterday. Also, you can use this plane (faces) to give an orientation if needed. Another aspect: if you were rendering an animation dupliframe will correspond to each frame

With the curve selected, under the Curve tab of the properties area, activate Follow.

Go into Edit Mode and change the curve's Tilt so that the curve's arrows are perpendicular to the shoe geometry. With a control point selected use Curve > Control Points > Tilt or Ctrl+T to do that. I suggest enabling Proportional Editing to achieve a smooth transition. (The tilt can also be changed after the diamonds are aligned, which probably will make errors more obvious.)

Change the diamonds' Rotation so that the diamonds are aligned with the surface.
XYZ angles of 0°, -15° and -90° seem to work fine.

To make sure that the curve is running at the surface of the shoe, add a Shrinkwrap Modifier with the shoe as target, mode being Nearest Surface Point and enable Apply on Spline.

You might have to move some of the curve's control points outwards so that the shrinkwrap modifier doesn't snap the diamonds to the inside of the shoe.

Final blend file:

I did notice @lemon 's suggestion of adding a plane array with dupli-faces after I started my answer and I do think that the plane array method is superior as it would allow you to use a shrinkwrap modifier on the planes, which again would allow you to skip the fixing of the curve's tilt. Or at least be much more sloppy with it.

Problem was it there were no dupliframe made by array after activating also. Any way thanks for both

@ateks, for the plane, not 'dupliframe', but 'dupliface' (which means duplicate the children objects for each face of the parent object)


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How do I make my pose symmetric?
I have already created the armature for this model and they are in the exact positions that I want them to be, so the armature itself doesn't need to be edited. However, the issue is that when using x-axis mirroring, the pose of the armature is not symmetric, like so:

One arm is always in front of the other whenever I try to change the pose. I must have accidentally moved one of the arm bones slightly when changing my rest pose. When I checked edit mode, I identified that the bones that are causing this issue are these bones:

Notice how the positions of the tails of these bones in the rest position are slightly different.
I want to edit the pose so that both arms are extended the same amount when I use x-axis mirroring for moving the pose (in other words, the rest pose should be symmetrical). But how would I do that? When I go into Item > Transform > Rotation for the bones, they both have the same rotation (since I assume they are calculated with respect to their current orientation), and therefore I cannot just copy and paste the coordinates from one side to the other. This is what I mean:

Here the quaternions for both these bones are (1,0,0,0), even though they have different orientations.
I am quite new to Blender, so right now I just don't know how to solve this problem without going through some complicated math or redoing the model. If anyone can provide me some insight into something I'm missing that would be greatly appreciated.

Update: I just found a solution. In pose mode, select the misaligned bone, then go to bone constraint properties and apply the copy rotation bone constraint. Then in the constraint properties, select the armature under the target option, then select the bone you want it to be symmetrical to, and then invert the y and z axes. Then use this tutorial to change the rest pose: https://www.youtube.com/watch?v=iMVs6BP1Q48&ab_channel=Chris%27Tutorials.


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Parent rigify part to empty
I'm working on an animation of a robot pedaling a bicycle. I have used rigify to
generate controls for the skeleton. I have added an empty to the rotating bicycle crank where the foot should contact it. What I'd like to do is parent the foot element to the empty, so that it will follow the rotation of the crank.
[

Hello, so what is your question? I guess you could use a Child Of constraint in order to parent the foot controller to the empty?

bingo!! Case closed!! many thanks.

Give a Child Of constraint to the foot controller bone with the empty as Target.


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EEVEE. Reflection of gloss surface in another gloss surface is causing weird bars of light instead of smooth lighting
As you can see in the render the "Stairs" on the left are being reflected in the shapes on the right but the light from the stairs looks like caution tape or something.  Is there any way to smooth that out so the lighting isn't broken up into those bars?

Hello, could you add a little more info about your lighting setup and the materials you used ?

I've added screenshots of the Gloss shader used for the platform and the Emission shader used for the sun.


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Is it possible to animate collection of objects that form a whole object that parts of are already animated with armature?
In this particular case i have a gun (collection of meshes) that parts of are rigged like trigger, shell ejector and top part shifting back. I want to add a recoil and tried selecting all the objects from a 'gun' collection and then keying rotation but parts shifted location somehow and everything broke.
How would i go about doing this the good way?

After trying to rotate along one axis: (doesn't even rotate)

E: I found some semi/very helpful comment here

I took a look at your model. If I was going to rig this gun, I would use 4 bones: a trigger bone and a clip bone which are both children of a gun body bone (all remaining vertices) which is in turn a child of a master bone. The only animation that the master bone is used for is the recoil; all other animations are keyframed using the other bones (reload, put away, aim down sights, etc.). I hope that makes sense.

So looks like i need to make a master bone and attach the rest of the stuff to it and hope it will work somehow

E: I found some semi/very helpful comment here

I took a look at your model. If I was going to rig this gun, I would use 4 bones: a trigger bone and a clip bone which are both children of a gun body bone (all remaining vertices) which is in turn a child of a master bone. The only animation that the master bone is used for is the recoil; all other animations are keyframed using the other bones (reload, put away, aim down sights, etc.). I hope that makes sense.

So looks like i need to make a master bone and attach the rest of the stuff to it and hope it will work somehow
Added new armature, selected all objects including armatures, ctrl-P then Parent-> 'Armature with automatic weights' and it sort of worked i think. Also the problem was i was using parent to object and then sort of manually adding armature modifier to meshes and selecting armature because it seemed to work.But i fixed some stuff by 'reparenting' children of master node

for this kind of obects, parent With Empty Groups seems better, then you just need to assign the meshes you want to the vertex groups you want


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Rotate object while following a path segment
I have an object following a path. I want this object to start and stop rotating at two specific points of this path. I could insert 2 keyframes normally, but I'm guessing that this could be done in a more general way?
Specifically, later on I will want to replicate this object many times changing the trajectories randomly within a window. And all of them should start the rotation when crossing an imaginary plane (say x=2), and stopping when crossing a second imaginary plane (say x=4).
(I am new to blender. Any suggestion or idea about where to start would be much appreciated)

So that all trajectories would share the start and end point?

The starting point of all the trajectories is shared (x=0,y=0,z=0). The end point will be different in 3D (but same in the x axes; x=6). But the segment with rotation will be in-between this points (from x=2 to x=4).

I can try to develop the animation of the different trajectories first. But there are different ways to do this, and only some of them will be compatible with the "rotation activated in a region". So I was hoping that you the experts could give me some advice @Lukasz-40sth

How to do this depends on the details of what you're doing, and how you want to specify the points measuring rotational changes.  I like to use a follow path on "fixed position" mode, and then animate the offset factor of the constraint.  If you're doing it this way, you can create a driver that interpolates between two different rotations on the basis of the offset:

I give Suzanne a follow path, on fixed position mode.  I create two empties with the same constraint, then use their offset to place them along the curve.  (Not by just translating them!)
Then, Suzanne gets two copy rotation constraints (world->world), targeting each empty.  The second constraint gets a driver for its influence.
I need three variables for this driver: the offset of each empty and the offset of Suzanne herself.  To create this driver, I can right click on Suzanne's second copy rotation influence and select "Create new driver".  Then, in the driver editor sidebar, with this driver selected, I can delete the starting variable and change the driver to a scripted expression.  To get each variable I actually want, I can right click in the offset field for each object and select "copy as new driver".  Then I can use the paste button (the second button to the right of "add input variable" in the driver sidebar) to paste these inputs into my driver.
After that, I set up my scripted expression.  I'm measuring the distance Suzanne has along the line, rescaled to the position of my first empty, rescaled to the length between the empties; I'm then using min() and max() functions to clamp this to the 0,1 range for the influence of the constraint.
Copy rotation doesn't always give you the interpolation you expect between 0 and 1. It's not wrong, it's just that 3D rotation interpolation is a more complicated beast than one at first assumes.  If you have problems with the interpolation of the rotation, there are other constraints you can use instead.
This gives you a tunable structure, where you can control the start and stop of the rotations, the length of the curve, and the exact rotations, all independent of each other.

thank you very much. This is much more detailed than I expected. I will work to implement your solution these days and post any follow-up comments if necesary


text:
Blender FBX Import messed up
So I'm trying to port the Voyager model by Eric Flat from 3DS Max in to Blender. And I've tried looking for a possible fix to this, however I've been unable to find a solution.
When I try to import the model to Blender this happens to it
This doesn't happen with other formats other than the 3DS format either. While I can use an OBJ format, the mesh is a little odd with it. I've tried ALT + G as well as clearing the LOC, ROT, SCALE values.
However the model itself isn't like this in 3DS MAX
I'm not sure why is this happening either, I've also ported another model from MAX using an FBX format, and it imported in to Blender completely fine.
These are my import settings
If anyone knows a way to fix this without changing to another format, I'd greatly appreciate the response.
Blender version: 2.79

There is no need to add 'Fixed' to the question or answer, instead, accept the answer that solved your problem.

I can't accept it until tomorrow, the FIXED edit was temporary.

The mesh parents were off center, and were fixed by moving them to the 3d cursor. Huge thanks to Pte Jack for figuring this out.

I don't understand. How did you fix it?


text:
Boolean Union not working. Subtracting instead of adding?
Tried looking this up on google, here, etc, etc, etc.
I have pics. Plain and simple question. I'm doing a boolean union and it looks like its subtracting the target if anything. I forgot to take a picture of it, but the crescent circle I'm trying to add actually worked on the other side of the oval. That is the vexing part about this. Any ideas?

Remove doubles, flip normal and then boolean

Same results...

Nevermind. Apprently it was someting wrong with one of those crescents. The one I used on the other side worked on this side as well. The flip and remove enabled that. Thanks.


text:
Blender 2.8 Cycles All Materials Same Color As Viewport
I don't remember changing any settings that I don't know what are for. The color of all materials is exactly the same as the one of the viewport background, ignoring roughness etc. This also occurs in final render. Eevee works fine, problem is only when using Cycles.
What have I done wrong? Any solutions?

I had the same issue, but because of something different. I did not realize I had Pause Preview enabled. Now I know that option exists too.

SOLVED
At some point I accidentally moved my objects to background layer. I had the transparent background turned on, so they got invisible. Moving them back to foreground solved the problem.

There are a few probable reasons why this is occurring.

If you go under the Object Data tab in the Properties panel, look for a material RGB color wheel/box. Check to see if the stored color there  matches your object's color.
Your Material may be causing this effect. You usually have to edit your materials so that the render engine can impemebt them properly. Make sure there are no problem with your node/material structure when using Cycles.
Check the "Draw Type" check boxes in the Object tab in the Properties panel. One of these may be causing this u expected result. Try playing around with them and see what happens.

Hope this helps.


text:
Save text logo for external use
I've created a 3D text with no animation, just text, and want to use it in my OBS when streaming. I don't know how to export it from blender to add it to OBS. Any help or suggestions would be appreciated. Thanks

I'm voting to close this question as off-topic because it seems to be more about other software than about Blender.

this is blender

I want to save it on blender to use on other software

It is unclear what formats are supported by Open Broadcaster Software so it is hard to guess how it should be saved. Is it a picture that you need or a 3d model?

I want to save my blender 3d text as an image such as jpeg or png or bmp but don't know how

You will need to choose the render engine, setup a camera, some lighting, materials for your text, chose the render format and it's settings as well as dimensions of the image in the Properties Editor, Render Settings tab, render it (f12) and save the rendered image from the image editor (f3). If you needed more help it would be useful if you clarified what parts of the process you needed more help with.

Using a non-animated image as a logo/overlay in an external program is generally pretty simple. From blender, all you should need to do it render it as an image with a transparent background. It should then be easy to add it to your program of choice. For example in OBS i found this: https://obsproject.com/forum/threads/inserting-a-logo-while-recording-a-video.19133/
For more info on rendering a transparent background see: Can Blender render pngs with the background transparent?


text:
How to Preserve Base Color of Non-Node Materials When Converting to Node-Based Materials?
I have dozens of objects (all curves, not meshes) imported with their own material and Base Color defined. I need to use nodes, but when I do, the Base Color changes to white, ignoring the color of the non-node material.
How do I keep the Base Color of a material WITHOUT node in the Base color when converting to a material WITH node?
Before:

After:

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There is reason to believe this post was not written by a human due to its structure, and grammatical construction, and has been marked by our community.
Current AI chat bots are a language models, that means they are like a parrot, they can mimic human language well, but they are built to write seemingly logical, seemingly factual grammatically valid text, rather than actually be correct, like a human would.
The veracity of the following content cannot be ascertained.
See the Concerns regarding AI generated content.

I managed to find a solution. I asked ChatGPT to create the script.
import bpy

# Iterate through selected objects
selected_objects = bpy.context.selected_objects
for obj in selected_objects:
    if obj.type in ['CURVE', 'MESH']:
        # Check if the object has a material
        if len(obj.data.materials) > 0:
            material = obj.data.materials[0]  # Assuming only one material is assigned

            # Create a new material with nodes
            material.use_nodes = True
            material.node_tree.nodes.clear()  # Clear existing nodes

            # Create the principled BSDF node
            principled_node = material.node_tree.nodes.new('ShaderNodeBsdfPrincipled')
            principled_node.location = (0, 0)  # Set the location of the node

            # Retrieve the base color from the original material
            base_color = material.diffuse_color[:3]  # Extract RGB components

            # Set the base color in the principled BSDF node
            principled_node.inputs['Base Color'].default_value = (*base_color, 1)

            # Create the output node
            output_node = material.node_tree.nodes.new('ShaderNodeOutputMaterial')
            output_node.location = (400, 0)  # Set the location of the node

            # Connect the principled BSDF node to the output node
            material.node_tree.links.new(principled_node.outputs['BSDF'], output_node.inputs['Surface'])

Thank you for sharing the solution (and for properly marking it as GPT this time), however it would be even better if you analyzed the code and modified it to better fit your question: 1) you don't really want to delete the default Principled BSDF node (and replace it with usually inferior Diffuse node); 2) no point to remove the output just to add it back; 3) the print statement doesn't seem very useful; 4) it could be all wrapped in a loop for obj in bpy.data.objects: or for obj in bpy.context.selected_objects:

@MarkusvonBroady Thank you for your assistance. Since the script was created by an AI and I have no knowledge of Python (0%), there is indeed much room for improvement. I have taken your points into consideration and updated the script to use the Principled BSDF. I believe it is slightly better now. Thank you very much for the feedback.


text:
How to add a Geometry Node to multiple selected objects (curves, not meshes)?
I have dozens of curves and I want to add a Geometry Node called test to all these selected objects.
The Geometry Node has already been created and I just want to add it to all curves that are selected.
How do I do this with Python script?

 Warning, Potential AI generated content⚠
This post is suspected to have been generated with the help of an artificial intelligence, chat bot, or other language model tools without proper attribution.
There is reason to believe this post was not written by a human due to its structure, and grammatical construction, and has been marked by our community.
Current AI chat bots are a language models, that means they are like a parrot, they can mimic human language well, but they are built to write seemingly logical, seemingly factual grammatically valid text, rather than actually be correct, like a human would.
The veracity of the following content cannot be ascertained.
See the Concerns regarding AI generated content.

I tried to create with the help of ChatGPT and came up with this script. In my case it works. The only way I managed to do it ON CURVES (not meshes) was by creating the modifier and specifying the node name for a single active object. Then, simply copy the created modifier to the selected inactive objects.
import bpy

# Select the active object
obj = bpy.context.object

# Add a new Geometry Nodes modifier
modifier = obj.modifiers.new(name="Geometry Nodes", type='NODES')

# Get a reference to the Geometry Nodes modification node
node_group = bpy.data.node_groups["test"]

# Set the modification node as the "test" Geometry Nodes node
modifier.node_group = node_group

# Copy the modifier to other objects
bpy.ops.object.make_links_data(type='MODIFIERS')

This doesn't answer the question (it doesn't APPLY the modifier, just adds it), and is an unmarked chatGPT content.

@MarkusvonBroady Oh, you are correct about "apply". Actually my intention was to "add" the Geometry Node modifier to dozens of curves at once after importing an SVG vector (that's why they need to be curves). As English is not my native language, it was a literal translation and I didn't realize it until you commented. I'll edit the question to avoid confusion.

It will apply all the modifiers (and convert the curve to mesh)
import bpy
from bpy import context

node_group = bpy.data.node_groups['Geometry Nodes']

for object in context.selected_objects:
    modifier = object.modifiers.new(name='Geometry Nodes', type='NODES')
    modifier.node_group = node_group

    context.view_layer.objects.active = object

    if object.type == 'CURVE':
        bpy.ops.object.convert(target='MESH')
    elif object.type == 'MESH':
        bpy.ops.object.modifier_apply(modifier=modifier.name)

Unfortunately, this approach doesn't work because an error message appears: "Cannot apply constructive modifiers on a curve. Convert the curve to a mesh to apply." The modifier is only applied to the active object, not the inactive ones. In my case, I need to work with curves, not meshes.
But I managed to find a workaround. Thank you, anyway.

@rdllngr in case of curves, replace the last line with bpy.ops.object.convert(target='MESH') - but keep in mind it will apply all modifiers (and convert the curve to mesh)


text:
How to increase render preview bounces? (Cycles in viewport)
Even increasing the amount of bounces in Render > Light Paths > Max Bounces, the preview of the viewport does not increase light. When I render the image the scene is much more brighter.

My scene is clean, no hidden lights in the viewport. I also did not change the exposure in Film.

Why is there such a difference? How to have a more accurate preview?
Thank you.

The bounces control should be shared. Are you letting the preview reach the full 128 samples before comparing? At low samples counts adding more samples can noticeably change the brightness of the scene, that may be what you're seeing here.

Thanks for the tip. It was actually Simplify that was limiting the viewport's AO bounces.

I found a cause of the problem. Simplify is active and limiting the number of Ambient Occlusion bouces in the viewport. I just match the values to get a similar render.


text:
During render can I render freestyle lines, then re-insert them back into the scene so other objects may interact with them during their rendering?
Clarification, May 31st 2017: User Firewill kindly provided an answer for the first version of the problem I stated, but I think I was after a more broadly applicable solution, so I'm re-stating my problem here in the hope that it helps solicit that.
As far as I can tell when using cycles freestyle to draw lines, those lines are placed on top of the rendered scene, so none of the objects in the scene get to interact with them in any way.
Take for example the scene below. The glass cube refracts light and effects the way we see the other items:

To emphasize the effect it has, let's overlay an image on the plane so we can see how the glass cube distorts and reflects a grid:

Super. Now let's see if we can draw that same grid with freestyle and see how it looks. First, take the plane, select its edges, and use "Mark Freestyle Edge":

Now render the scene. Oh dear, that's not at all what we were after. No distortion of the grid, no reflection of the grid, no hiding or coloring of the grid.

So, my question is, could I use compositor to render the plane and its freestyle grid together, then "re-insert" it into the render flow so that it can interact with everything else? Giving us a result like this, but with all the benefits of freestyle:

If it helps, here's the blend file for that scene:

Thanks very much for any help you can offer.

Original question: I have a mesh terrain, and a cube that intersects it to form the surface of a lake.
Here you can see how I've roughly thrown that together, with the cube placed underneath the mesh, poking through it to form the lake surface:

Here's what that looks like when it's rendered:

I'm then using freestyle to draw lines along the terrain's visible edges. Unfortunately the lines aren't drawn beneath the surface of the lake water, because freestyle thinks they aren't visible.

To correct this I initially tried using the QI Range setting in freestyle to additionally render the lines below the water, however that came with two problems: firstly other unwanted hidden lines in the scene were also rendered (those hidden behind the hills); and secondly the lake bottom lines were drawn on top of the water, and so didn't appear to be "hidden in the depths".
Here I've rendered only those hidden lines, to illustrate the problem:

Since I couldn't solve my problem with QI Range my next thought was to render the terrain and freestyle lines as one image, the water as another, and then combine them in the compositor.
However, while I've done some simple experimenting with the compositor, I can't for the life of me think how to achieve the effect I want with it. Does anyone have any advice? Or am I trying to solve this in a silly way?
Here's a blend file where you can more clearly see what I'm working with:

Update, May 30th 2017: I've done some more fiddling and broken out the land, water, and freestyle lines into their own layers. I'm rendering then combining the land and freestyle lines (which works great), and then trying to add in the water afterwards. However that step doesn't really work out as I just end up with a cube of water plonked on top of the land, and the lake floor in that part doesn't include the freestyle lines (I'm not sure how to get them in there).

Here's the file that produced all that:

I'm sure I'm missing a pretty obvious bit of knowledge about how compositing works. Could anyone with more savvy in this area explain what I should do to get all of this combined?
Thanks for any advice you can offer.

It looks like you're trying to make freestyle lines being refracted by Glass  (or whatever you have on the cube) shader. That's impossible afaik as Freestyle is another render engine which doesn't interact with Cycles or alike. Maybe it could be possible to set refracted object to separate ObjectID, render usual refractions and trace them (like with vector graphics) to make lines into additional image which to process with freestyle or something.

I agree with @MrZak - the Freestyle lines are added post-processing after the render is complete so cannot interact with the refraction in any way - in fact, the freestyle lines can even 'bleed' out over the edge of the rendered geometry and so is not even necessarily relating to a face in the rendered image (consider setting the line width to something like 20 pixels - half the freestyle line would overhand the actual face) so you couldn't even bake it to a texture to feed back into a second render. An alternative would be to use procedural texture to draw the lines rather than freestyle.

That's good to know. Thanks very much to both of you.

So I broke up the scene into 3 render layers:
A freestyle render layer which just renders the lines
A land+water which renders the land and the water without lines
And a land layer which is used for depth
Then mix like this:
we use land + water as a base, outputting a material index so we can mask the water area.
material index:

Then using the alpha channel of the freestyle layer we mix the original output and the colors we want for both above water and below, using a material to output the depth of the land enabling us to interpolate between surface colors and depth color on the water covered surfaces.
depth land material:

these are the compositor nodes:

and this is the result:

of course you can tweak the colours of the lines and make it look non-terrible :P
Hope this clears up your doubts!
(if you want the file I can give it to you, but I probably broke any kind of settings or order that you had)

Firewill, thank you so much for your answer – I really appreciate you taking the time to help me out! I realize that while your answer solves the narrow problem I stated, it doesn't solve the larger problem I was trying to ask about. I've changed my title and examples to better reflect the larger question I have.

I did find your answer to be super useful though, and I'll be using that technique for other things, I'm sure :) I'm just sorry that I didn't realize that my question was probably too specific was until I saw your clever solution.


text:
How do I stop a displacement modifier from breaking the edges of its mesh into many small parts?
I have a mesh grid. I have selected all the edges of it that run in one direction and applied a freestyle color mix to them so their start is pink, their middle is white, and their end is green.
When I view the rendered mesh like that I can see that each edge is rendered as a single line, with all the colors nicely lined up:

Now I apply a displacement modifier to the mesh, using an image. I would expect that each edge would remain as a single, uninterrupted line, warped to fit the displacement map, and with the color placement the same as above – pink on the left, white in the middle, and green on the right.
Instead of that I see a random distribution of colors, indicating that my edges now appear to be made up of many small lines:

How can I correct that and achieve a displaced mesh with single, unbroken edges running the full width of my mesh?
(FWIW applying the displacement modifier has no effect on the issue.)
Update: May 7th, 2017 – I tried turning off the "Visibility" setting, as per TK's suggestion, but that didn't fix my problem. The lines are still mostly broken up into small pieces.

Here's another version of the file that I created from scratch, just to make sure I hadn't unchecked any default settings while fiddling about. It exhibits the same problems. I've applied the Displace modifier to keep thing simple.

Thank you.
Dunstan

With the displacement modifier, the edges are occluded by bumps created by the modifier and hence are no longer fully visible from the camera.  Freestyle identifies both visible and hidden lines, and by default draws only visible lines.  If you want to draw all lines no matter whether they are visible or hidden, then you need to turn off the selection by visibility (i.e., disable the "Visibility" toggle in the "Selection By" section of the Freestyle Line Set panel).
Update on May 12, 2017
Setting the mesh faces to the smooth shading and turning on the Face Smoothness option could improve the result as you expect.
That said, there seems a bug in Freestyle that prevents visible and hidden lines from getting chained into a single stroke.  For instance, the following render shows lines composed of visible and hidden parts.  Most lines are consistent in the sense that they start in red and end in green, while some lines are not.

The next image shows some of those inconsistent lines that are expected to be long continuous red-green strokes rather than being split into short pieces.

The render below shows the visibility of line segments in question (visible and hidden parts in red and green, respectively).

By comparing the last two renders, it is seen that in some cases visible and hidden line segments can be chained to form a consistent line, while not in some other cases.  I think this is a bug in Freestyle (to be fixed as soon as time permits).

Thanks so much for getting back to me, TK. Your suggested fix makes complete sense, but unfortunately doesn't seem to work. The lines still appear to be broken into many small pieces, as indicated by the distribution of the pink and green colors. I've updated the post with some (hopefully) clearer graphics and also a test file.

TK, that's wonderful! Thank you so much for looking into that again in more depth. I'm sad to see my problem is the result of a bug, but I'm happy to see someone else successfully duplicate the issue. I'll try and work around it for now and hope a fix is lucky enough to sneak in to an upcoming build.


text:
A mishmash of questions about lighting and messing with parallel line textures
I'm brand new to Blender (and 3D modeling). I'm attempting to use it to duplicate this graphical style (not my work):

I've created my terrain, and experimented with a variety of node tutorials to produce a series of lines. This is my current node setup and resulting render:

I have four questions:

How do I remove all the shadows from the final render so I only see my white and black lines and nothing else? – I've killed the lamp and set the material to emit (this was the only understandable way I could find to remove shadows), but I still see gray areas in the final image.
How would I get the lines to stay a constant width? – They currently get thicker as they run over terrain sloping perpendicular to them. I'd like to see a version with a constant line width, if that's possible.
Is there any way to introduce an element of randomness into the lines (shake, spacing, or thickness), so they look more hand drawn?
How would I get the render to show perspective? – I want the perspective to be more pronounced so the lines closer to the camera look spaced out more than the lines in the distance. I expect this is a camera setting but I find the camera stuff rather confusing.

Thank you for all and any help you can offer, and sorry if I've posted too many questions in one go.
-- Dunstan

Hi. Please only ask one question per post. I suggest editing your question to remove all but one question and then re-ask the remaining questions, each as separate posts.

#1 I think you got the general setup right, you use an Emission Shader node down to the Light Path node, but made a mistake in your setup. Down the nodetree you later mix the emission with a diffuse defeating the purpose. Also your node tree seems overly complicated, and unnecessarily convoluted for the setup.

#2 As Jerryno already mentioned, it is not trivial to do with material nodes alone, but see bellow.
#3 Add a Noise node to your texture coordinates, use a Color Mix node to control the amount of noise you add to the coordinates. Some scale change is to be expected, so compensate the size.

#4 Camera settings like Focal Length will dictate the perspective

Alternatively if you want true constant width, and don't mind a geometry based solution, convert your terrain to a mesh, select all the edges in one direction, and erase everything else. Convert it to a curve then use the Bevel Depth property to add constant thickness.

Holy cow! :-O I'm amazed that you went to so much trouble to help me there. Thank you so much! That's all going to be a tremendous help!

For future reference it is advised that you break different question apart and post them separately. As as many as needed

This is working out great, thank you again! My next step is to try to figure out how to create a solid white surface underneath the extruded lines, so the ones on the backside of the slopes aren't visible.

Just leave a copy of the original mesh you extracted your curves from in place. That should occlude the backfaces and align perfectly. Then assign it a plain white emission material, similar to the one you already created with a light path.

You are correct with using just the emission shader. If it's strength is 1.0 and it has only white or black color there should be no grey.
This is not easily possible (it is possible but it is not trivial - by using the slope from normal input). It's better to cut edges into the surface in the direction of lines and shade those edges with Freestyle, or you will have to create curves on the surface and render them as black pipes on white ground. You can use a plane and array modifier to get your slices, then boolean them with your surface to get the edges or curves (convert edges to curves).
You can use a noise texture mixed into the mapping coordinates. Or you can use a noise on those edges or splines (displace modifier with noise).
This is in camera settings. Position the camera closer to the surface and set lower Focal Length. This gives you bigger field of view, which pronounces perspective.

Actually about #1 his node setup is incorrect. He does use an emission shader with a Light Path and all, but then mixes it with a diffuse later down the node tree, defeating the effect

Thanks for the answers, Jerryno! I'll look into 2, 3, and 4.

Duarte, would you happen to have a suggestion to correct what it is you say I'm doing wrong? Thank you!

I do, see my answer bellow

Having looked at the mesh I realized those grey areas represent holes where something must have gone wrong when I initially built my terrain. Just thought I'd pass on the finding.

@DuarteFarrajotaRamos Yep that material is wrong. I misinterpreted his question and thought he was asking about whether emission shader is the right way to fix the material.


text:
Getting divider line between 2 mirror
Im making a simple model. I have added subsurface and mirror modifier. Im getting a divider or partition line between 2 mesh. I have on the clipping and merge in the panel. How can i dissolve the divider or partition line between. Any suggestion. Thanks (Please do not tag duplicate plz reply with comment or answer)

Try increasing the clipping limit

@DuarteFarrajotaRamos can you tell how it is duplicate question and i have request not to make it duplicate tag so plz answer with my model. Thanks

@atek This site is not just for fixing models. It is for you to learn how to do it yourself. If your question is marked as a duplicate, go to the duplicate, understand what the answers there say, then fix your model. If you have any problems, come back and ask a specific question about that issue or post a comment asking for clarification on another answer.

Your problem has 2 origins: the simpler is that the subsurf modifier should be after (down) the mirror modifier. The harder is that the mirror modifier uses as mirror pivot point the origin of the object, and your mesh is not in line with the axis. You can  solve the issue in this way:
switch to top ortographic view (toggle Numpad7 and 5); rotate your mesh until is quite aligned with the axis; in edit mode select the center line and scale it on the x axis by 0 (S,X, 0, Enter); put the cursor aligned with this edge loop (Shift S, cursor to selected, then - in object mode - set origin to 3D cursor); select the edge loop next to the central one and dissolve it (X, dissolve edges).
It's always a good practice to mantain the origin of the object in the center of the scene during the modelling phase, then move objects to the desired position.


text:
How to convert follow path to object
How to convert follow path to object I have made a add object constraint follow path and given the path. I dont want to animated it. I want that mesh to be used. How can i delete the path and used the mesh that is created. An image i have attached with the follow path i have made the sphere a shape and i dont want that path just the sphere i want with that path shape. I want to convert to a single object. ctrl+j not working and if i delete the path ever thing disappear
blend file ...

which modifier may i know can u plz make it clear in brief

Select all your meshes, Ctrl+A to open the Apply menu, select Visual Transform. This will apply the constraints, but you still need to remove them (they're applied AND active) with Ctrl+Alt+C.
Then you can join them with Ctrl+J.

In object mode press "alt+c"

authors: Михайло Жилкін


text:
I cant add loop cuts
 I have a model and want to shrink or press or bend on red axis show in the image to make the shape as shown in reference image. I cant add loop cut & if i add sub division modifier i loose all the sharpness of the edges. U can try with my model i have attach the file.....
Added lattice and modified little bit to get the shape

confused problem

with the reference video i have yet to error

press Shift+A and add a lattice

after that, select the object to be deformed and add a lattice modifier
 Under the modifier, make sure you select the lattice as the object  select your lattice, and go to edit mode, pressing TAB key; press Shift+leftclick to select the 4 vertices on the -Y direction of the lattice, press S to scale them. I've uploaded your blend file with the lattice:

yes thats what i need thanks learning from expert is great

Im little bit confuse with my file or with the method plz i want to confirm as i do not want mean time my problem to be solve i like life time problem to be solve when ever i use it should work same way and with perfection. As in the image i have taken the lattice and add 3x3 cut and then i click on my model and add the lattice modifier. going into the edit mode as i see that the corner when stretch it works but with the center it did not work. Sorry for repeating the question again. What im doing is the correct way or can u plz explain whats the correct and where im going wrong

instead of 3x3, try 4x4 and scale the middle group of vertices. Do a lattice form like this one: https://www.youtube.com/watch?v=-NbzlQVmloE

as seen in the video i have did still error i have attach the file and image whats the problem going on

Under the lattice menu (between modfifiers and texture icon), change your values (U,V, and W) to 4, instead of 3 (like the lattice in the video). Then select all the vertices in the middle (remember to select the ones on the other side, and the ones in the middle), press S to scale.

Can u plz download my file http://blend-exchange.giantcowfilms.com/b/2192/ and see the error i have made the section but the middle section not working only the 4 corner are working

i got the solution i subdivide the model 2 times and then add the lattice modifier and got the shape. Thanks

You dont have a pure quad mesh. Loop cuts will only work with a mesh that the faces are 4 sided, and what you have is a n-gon mesh (sometimes 3 sides, sometimes 5 sides, or even more) - you have to remesh to a pure quad mesh, consider retopology techniques using mainly squares or rectangles to build the mesh. Another problem is your normals, that are not consistent: while in Edit mode, select all, press space write "consistent" and select "make normals consistent"; or recalculate the normals. In case you don't want to do retopology, you can add curve objects and use modifier deform by curves, or even add a lattice object and deform your "steel object" by it, using lattice modifier.

Yeah ur right i don't want to do again. lattice is not working i tried it. can u tell me modifier deform by curves how it works i never used it

well, I just performed the lattice modifier to your object and it worked. I'll add another answer explaining how to. wait a bit

i have attach my result file

Well done! Next time, you want to model something like this, remember the quad rule! The tricky parts will be when you want to perform boolean modifiers, like the circles you carved! you have to match the number of vertices to neighbour number of vertices, to keep quadrangle faces. Please look for tutorials on retopoly faces, and see how they manage around the eyes.

other thing, when you apply subdivision surfaces and you want to get some sharp edges, select the edges you want to be sharp, press N (for right lateral menu), under "transform", increase the "crease" value to 1, and that edge will be sharper than the others.


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Why shrinkwrap not working on the mesh
I have a mesh and a plane that i want to shrinkwrap on that mesh. When shrinkwrap added its not wrap in the shape model. To the side its cut shape and not fully covered. On the top some part it got shrink and some not. Any help or suggestion plz Thanks

unrelated, if using "project "on surface" be sure to select an axis (none are selected by default)

Are you shrink-wrapping to a single object? You're only allowed a single target object in the shrink-wrap modifier. You can duplicate and merge your objects for the shrink-wrap process; that way, your original model state stays intact.
Also, if you are using other modifiers, play with the order of your modifiers by using the up and down arrow buttons in the modifier panel. I believe modifiers occur from the top down.
Lastly, the shrink-wrap modifier can only work with the geometry its given. subdividing your sheets will add more geometry and give you a more accurate wrap.
Hope this helps!
EDIT:
After downloading your file and applying the methods I described above in a few clicks, I achieved the result you were searching for. There was not enough geometry in the 'sheets'. Also take note of the offset value in the shrink-wrap modifier. see image below:

I have attach my file in the question section can you go through it and clear. Thanks

Thanks for replying with the image. The plane is not covered the below mesh its look cut from the side. I have attach my the file with red mark i need it to be covered completely.

@lemon can i get the answer for the question. Thanks

Please TRY before asking additional questions. Think about your scenario. you're using the shrink-wrap modifier. It behaves like shrink-wrap. if you want the sheets all around the object, Then turn the sheets into tubes so that they shrink-wrap from all sides. done.


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How to create a model from drawings just like Smoothie-3D, Paint 3D or Monster Mash?

I want to find some way to imitate this technique. (draw a curve that becomes a model with a few clicks)
The same can be done with Paint 3D as seen here and Monster Mash as seen here.
The most I can do is convert the Grease Pencil to mesh and with the vertices create a plane, but inflate it is so hard.
Does anyone know a method to imitate in Blender what is done in Smoothie-3D, Microsoft Paint 3D or Monster Mash?

Okay, I finally figured out how to do it. I hope the explanation below can help other users. To understand the process in more detail, I recommend the tutorial "Blender Sculpting Tutorial: Full Advanced Creature Creation Workflow" by CG Boost on YouTube.

With any model selected, in Sculpt Mode with the Lasso Trim tool, I change Trim Mode = Join and Shape Orientation = View in the header. Enable Use Cursor for Depth if you want to control the length of the model in proportion to the radius of the brush. The smaller the radius, the thinner the object will be.

Then I draw the shapes to create the silhouettes.

To rearrange the mesh, I use the Remesh command (header) after defining a Voxel Size.

And finally, to smooth and inflate the model to disappear with the hard edges, I use the Mesh Filter tool with Filter Types = Smooth / Inflate. Keep X/Y/Z active in Deform Axis and Orientation = View.

From there, any adjustment of scale, rotation and proportion can be made in Object or Edit Mode.


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How to Export this to fbx Unreal Engine 4
Hello guys, i'm very new in blender so can you help me please, i have no idea how to export this to unreal, because I still can't understand how the nodes system works,and what exactly this mesh is.
I created a skull, and want it to move in my game with smoke behind it, so i add a quick smoke and its absolutely works in Blender, but I don't know how to put it in FBX and should I create smoke in Unreal?
Is there a better and easier way ? In the end I want this skull  to move so it will make smoke behind.
Please if you can't give me an answer, a simple advise can be good too :)

FBX only exports geometry, UVs, some animation properties like rigging, and very basic material properties. Smoke simulations, particles, physics and other specifics of Blender can't be exported, through FBX nor most other formats for that matter. Bottom line is you should be able to export your skull, but everything else you have been wasting your time. unfortunately. It should have been made in game engine, not Blender

Also see http://blender.stackexchange.com/questions/57531/fbx-export-why-there-are-no-materials-or-textures

@DuarteFarrajotaRamos could you add an addendum to that post with your comment thanks. Making that the new master for dupes.

Just did, feel free to make any corrections you feel necessary. Thanks


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Weird lines shows everytime when I try making a Glass Object in blender

I imported an object from maya and created a material in blender...and when i turn on the alpha blend option i get these wired lines every time.
I already tried flip normals ,recalculate normals , shade smooth , alpha hashed but these lines are still there
I want to export the file in glb format from blender and these lines are still showing up there
Here is the link for blender file
https://we.tl/t-OGJRmYd7JW

I tried following your instruction and got good result in blender Thanks.... but when exported in Glb format these are still visible.

Is this render engine problem or what?

Glass in Eevee needs tweaking, if you remove the Show Backface it will fix your problem but you won't see your own object by transparency, I hope someone has a proper answer

a hack would be to create a second object for the inner surface of your object, see Bibi's answer here (french, donwload his file): http://blenderclan.tuxfamily.org/html/modules/newbb/viewtopic.php?topic_id=50729&start=0#forumpost589337

So I'm not sure there's any perfect solution for your problem, but here is a trick proposed here by Bibi.
If you disable the Show Backface option you'll get rid of the artefacts that you're talking about but you won't see the glass surfaces by transparency, so you still have a problem:

The trick is to separate your glass object in two separate objects, the outter and the inner surfaces...

and you'll get that, which is rather good:

the file is available here:

Thank you so much this method solved my problem....

change the blend mode of your material to alpha hashed.
Then you will get:

I changed the mode to alpha hashed and exported it in glb format(as i need glass object in Glb format) But these lines are still there

you didn't write anything in your question that you do export your file, and nothing about glb format. So you should improve your question....!

Thanks for the suggestion.... I improved my question


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Weird Offset when Using a parenting bone script
there are two cubes on the same spot

but
When I use this(similar might not work if you try)
def parent_set(object, armature, bone):
    object.parent = armature
    object.parent_bone = bone
    object.parent_type = 'BONE'

objj = bpy.data.objects
parent_set(objj['object'], objj['Armature'], 'bone')

it does something like this

How can i fix this

batFINGER the armature is in the picture it looks like it parents it to the head but it isn't consistent it sometimes puts it on the some "random" spot

Try  my answer on same question you gleaned your question code.

i got the this version of the code from your answer

so i found something that when i apply the transforms it puts it on the head

but it kinda brokes my code

To me it looks like the accepted answer, which pointed out the error in my first answer version (which was parenting to head) After which added  a long winded edit on getting different results. The "random" offset you are seeing is quite likely the basis matrix of the cube.

so how can i fix it btw my original code uses def parent_set(object, armature, bone):     object.parent = armature     object.parent_bone = bone     object.parent_type = 'BONE' objj = bpy.data.objects     parent_set(objj[str(1+i)+'_obj'], objj['Armature_pyhs'], str(1+i)+'_bone')

hmmmm i changed the post to "original form with some grammar fixes" and i tried your script and it did the similar thing

Apologies, was missing the wood from the trees, will edit prior answer.

so i botched it instead i just changed location of them (the objects that are parented to the bones) and added a different script that parent the objects to the with Automatic Weights


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How can make the mortarsmooth overlap the edge of a brick?
I want to make some cartoonish bricks.
I want the mortarsmooth a bit more natural. The problem is those thin lines of a different part of the colorramp.
If I change it via a map-range node, I am only getting full coverage when I have the  from min-point at 1; but then I have  straight lines again.
Did I miss something?
My goal is that each color is just sit in one brick by itself.

maybe a sketch/picture how it should like would help here. Because i still don't really get it what you want..

@Chris, I made a edit, to clarify my problem.
Hope it helps.

This is a very similar approach to @Markus von Broady's.. (answering at the same time :) ) .. but perhaps it's different enough to be worth posting.
It branches a parallel Brick Texture, in monochrome, concerned only with mortar. In the second branch, the mortar is enlarged, and softened. (That's a 'distance from rectangle edge' function, internally.) The softened mortar is multiplied with some kind of greyscale noise, and put through a threshold, to generate a mask. The mask mixes between your chosen mortar color and the original Bricks:

All the spaghetti is just to keep the textures in sync. There are some parameters which have no inputs, so can't be exposed in the group interface. Those are paired using drivers. To adjust those, you would have to make the group single-user, go inside, and tweak in the top texture node.

Of course, you may want to change .. e.g...  the kind of noise, to change the characteristic bleed. For more control than this sort of thing though, IMO, it would be better to create our own procedural toon bricks from scratch.
Here's a .blend with the above example settings.

Great setup, thanks a lot.
how exactly did you set up that those two bricknodes are matching certain parameters?
by trial and error i found out, it has something to to with the driver-editor, but its a complete new field for me. maybe you can give me a small insight? (:

@vp.gestaltung   Right-click in source field > 'Copy as New Driver'. Right-click in target field > 'Paste Driver'. It can get more elaborate than that, with the editor to adjust, but this is a simple one, with a 1:1 relationship. Works in just about any other field in the UI.

Great, learned something new today, I think i will benefit from it in the future.

You're generating a grayscale brick texture, then apply a color ramp to convert various shades of grey to various colors. It works only as the mortar color and each brick color is unique. Once you smooth the mortar, part of the range of its color "leaks" into the luminosity of other bricks...
So if I understand your problem correctly, you can solve it by using two Brick Textures - one generating the bricks with no mortar, and the other generating only the mortar. Then use the latter as a mask:

Using a Custom Group just to keep all the common settings in a single place:

Thank you, i understand it a way better now.
i build what you explained, but i have a followup question:
but is there a chance to get a clean edge in this easy setup?

@vp.gestaltung I think applying some threshold (not necessarily 0.5) would work. https://i.imgur.com/UXqh5St.png

Awesome, i am amazed how simple it was!


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Showing just black silhouette of a model without adding new material
Similar to other creative approaches it good to get a look of your model/ design just by seeing the silhouette.
I want it directly in the viewport as quick, easy way to see, without adding a new material and changing the pass index or any form of shading.

In the viewport shading settings turn on shadow to 100% and changing the shadow shift to 57° (all the way to the right) to get a pitch black model in the viewport.
Together with turning off the viewport overlays, you can brainstorm/ model something without shading or distractions.
If you add both options to your Quick Favourites, you have a easy check occasionally.
(I put both in the quick access while in edit mode, I have less favourites there, so its easier to choose them there)
Also works with ( beveled) curves and any other object.
Be aware, that if you work longer in black, might be overlapping geometry or other issues, that looks good as a silhouette, but not in 3D.
A good way to limit this, is to work from orthographic view, turn on face orientation or just use a extra window just for that purpose.

The trick with viewport shadow works great for low-poly and mid-poly meshes, but it causes immense lags with the dense (sculpted) meshes. Hence, to avoid lags, instead of viewport shadow I recommend to use Flat lighting  (more details in my answer)

For viewing silhouettes I recommend to use Flat lighting.
This option is superior to viewport shadow, because viewport shadow could cause lags in case of dense meshes, while Flat lighting doesn't have this flaw. And less important but also nice thing - Flat lighting gives you an ability to adjust the color of silhouettes.

Detailed instructions:

in the upper right corner you can change lighting to Flat

then Color > Single (and set any color of your choice, e.g. black)

plus it could be useful to disable overlays :

before/after:

*to revert settings back - choose Studio and Material:

and turn overlays back :

That's it :-)


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Why isn't Face Sets painting all the faces under the brush in Sculpt Mode?
In Sculpt Mode, when using Face Sets Brush on the mesh, the mask does not apply correctly to all faces below the brush. Some faces are ignored. This happens with any new object that I create.
I already tried to reset the presets of this brush, but it still fails. Is there an option that I accidentally checked that creates this problem?

Ok I got it. In Brush options of the header bar it is necessary to UNCHECK the Face Sets and Face Sets Boundary checkboxes. It is also recommended to have a not too high Strenght if you want to smooth the Face Sets (when holding Shift with the brush).


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why adding sub surface getting this result
i have a simple extrude geometry The mark in red is the sub surface added and without red mark is the original mesh. After adding sub surface to it and im getting odd result. I have remove doubles normals are fix whats the problem. The mesh are united at center. Any solution

The top and bottom faces of your mesh are single Ngons.

Change them to quads and the subsurf works as expected.

@ OP: after you have filled the first quad, you can select the short edge (between the first and second quad) and consecutively press F

@3fingeredfrog thanks for replying how to change quads

"how to change (to) quads" (?)

Edit mode > Face select mode> select Ngon > Mesh menu > Faces > Triangulate Faces. Then convert those triangles to quads. With the triangles still selected: Mesh menu > Faces > Tris to Quads. Repeat for the other Ngon.


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How can I solidify without ruining spiked edges?
I'm trying to poly model a helmet and I have some extruded spiked edges but when I try the Solidify modifier, my spikes get horribly messed up. Is there any way I can exclude them from being solidified? I've tried to hide them with H but since the modifier applies outside of edit it didnt do anything.
Here is the helmet without being Solidified:

Here it is when Solidified:

I tried checking only rim but that doesnt accomplish what I'm after, which is making the helmet somewhat solid to be printable. I'm not yet familiar with all the tools available so I dont know where to go from here. If I can have a solid interior without the spike distortion it would be perfect.

Hello :). It can be kind of done, moving the Subdivision modifier after the Solidify modifier and using Clamp. But it has limitations, creates overlaps, etc... I posted a full answer with  a more elegant solution.

I would Solidify the outer side, and adjust the spike manually.

Use the Solidify Modifier.
Set Offset to 1 and adjust Thickness to your liking.

You can adjust Inner/Outer Crease, if you're also using the Subdivision modifier.
The Subdivision modifier should be AFTER the Solidify Modifier.

Hit the Apply button to apply the Solidify Modifier.

Go to Edit mode
Select the new vertices and scale it down to make it pointy using the Scale Tool.
Shortcut: S

Thank you, this worked best to get closest to what I needed. I didnt know how having modifiers in different orders would affect the model.


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Animated World background color doesn't show in the viewport
I wanted to change the background color over time, according to a sine wave, fed in a mix shader. The problem is, even if i added keyframes to value to change over time, the animation is doing well, but in the render tab, background color stays the same. Does somebody know where's the problem ?


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Animate an object array along a path with curve modifier
I'm working on an industrial conveyor belt and trying to animate it but can't figure out how to make it run.
It's a single object with an array to multiply it, deformed with a curve modifier.
I tried pretty much avery axis to move it, but it either stays still or move on the side.

I found the problem, in my curve settings i ticked "Bounds Clamp" and that prevented me from moving my object in the correct axis. Thanks lemon !

You can parent the belt to another object (an empty for instance).
Then simply move the empty in the appropriate axis (along x in the blend file attached below).

You can also move the object itself along the same axis.

Thanks for your answer, but my problem persists, the axis into which I want to move the object is locked. I tried applying the rotation and change de deformation axis but it doesn't seem to work better..

@ThibautTuabit, you should upload your blend file (editing your question) so that we can have a look at your issue.

Sure, thank you


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2 curve 2 different results
I have 2 curves name Top curve and Bottom curve and bevel with name bevel pipe. In the curve bevel i have given both the curve same bevel but the result to the top is thick (yellow color) and the bottom curve is thin (grey color). Any solution

Have you done ctrl+a -> apply scale while selecting both curves?

Edit:

Select your curve
go into edit mode
with all Points selected press "w" and select "Set Curve Radius"
Change the curve radius in the operator panel

to reset the curve radius divide 1 by the scaling factor, in this case the scaling factor is 2.048

its not working with the scale

Oh, didn't look closely enough. My bad.
when you scale a beveled curve, it automatically scales the curve radius.
You can set the Curve radius by pressing "w" in edit mode.

can you answer me in more details with image or gif

edited my answer above


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Why can't I create a pipe from this curve?
 I have created a bezier curve and small circle. I want that circle take the shape of bezier curve so that the curve becomes a pipe. In the gif you will notice that its becoming flat, not like a pipe.
What is wrong with my settings?
Blend file

For this setup to work, your circle has to lay flat on Z axis.Like this:

And it has to have this rotation applied, so you can rotate it in object mode and press Ctrl+A and choose Rotation or rotate it in edit mode. It will have exactly the same effect.

It work. But before it was also on the z axis but was not flat. May i know how it works little in details. Thanks

It basically works like you would draw bevel shape in 2d from top view in local space. So if it lays flat, it makes full, nice circle.If you rotate it a little, form the top view it makes an ellipse and so the bevel shape looks like.In local space means in this example Edit mode space and in general, it's set of coordinates in relation to the object own pivot point unlike world space, which is set of coordinates in relation to world center.


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How to select the edges in my circle

I have a icosphere and in that there are 3 types of 6side star shapes. Large medium and small. In the stars there are edges and i want to remove that edges. I have remove the large star edge selected a single large star edge and shift+g and length and delete all the edges. The same process not working with the small and medium star. I can select manually and delete but i dont want to do it. How can select the edges at few clicks. blend file

Switch to Vertex Select.
Select center vertex in small star.
Hit CTRL + Numpad +.
Shift + G > Amount of connecting edges.
Switch to Edge Select and delete them.


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why shrinkwrap not getting curve shape
I have a oval shape with needful verts on it and a cylinder. I want to make the oval shape to wrap on it. Little bending shape with only shrinkwrap modifier.

When i add shrinkwrap modifier it looses its shape. Any help or suggestion how it works.

maybe because you've chosen the Nearest Vertex mode?

I suppose it's because you have chosen Nearest Vertex mode in the modifier, so the vertices of your oval stick to the vertex of your cylinder mesh. Switch to Nearest Surface Point and it should work properly.


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My object becomes darker during animation
I have made this animation:
https://i.imgur.com/qXzYD8o.mp4
Each frame consists of an object that has been generated independently using python. These objects are isosurfaces of a function at different points in time (it is a rabi oscillation for a single electron in a molecule as the molecule moves from a ground to an excited state). The algorithm used to generate the surfaces provides me with the list of vertices, normals, and faces that define the surface.
There are two emission planes, one below and one above the object. The renderer that I am using is Cycles.
I do not understand why some of the objects appear darker. Could it be that the normals are pointing in the wrong direction in those objects? If that is the case, is there a way to ignore the normals?
EDIT: This is a blend file which contains two objects from two sequential frames. One object appears darker than the other:

Hard to tell based on the provided gif. I guess either the geometry has a few glitches, the lights are not big enough (I'd suggest using area lights) or the sample count is too low and the denoiser introduces some artefacts... If possible share your blend, ideally using https://blend-exchange.giantcowfilms.com/

please provide blend file

@Chris Thank you for the suggestion. I have done so.

So, when you generate objects, you made them without normals. I don't want to say, that they have no normals completely, because mesh can't be without normals. What I see, that all normals are rotated in the same vector, so your objects look completely flat:

But what causes the jittering in colors? This vector is different from one object to another. This mean that your object is shaded completely flat as a single plane can be, but each time the plane is rotated in a different angle.
So, how to fix that, depends on your code. I guess you should use update function (update(calc_edges=True)) to update normals, but maybe I'm wrong. I noted, that clearing custom normal data (in "Geometry data" section) force normals to be recalculated:

You might be wondered why if your object shaded flat, you still see some shading in the render? It is because ambient occlusion still have effect even without proper normals


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How to cast/teleport a ray in a material for a squinching illusion?
In short I'm wondering if there's a way to not only refract a ray, but also moving it, or somehow cast another ray from a different position in a material shader for an illusion I'm working on.
This situation is pretty complex but I'll do my best to explain what I'm doing.
I'm working on methods to implement squinching, a way to trick the viewer into thinking that a curved (projection) screen, isn't a screen, but extends into a larger 3D world (Like with the Trompe L'oeil illusion).
You can read more about what squinching exactly is in this expired patent: https://patents.google.com/patent/US6462769B1/en
I already got most of it working. I set up a simple shader for the screen, that refracts the light in the opposite direction from the viewer's position (the audience position)

The current result is already working really well, however one situation isn't covered yet.

The render camera (Marked with a P) shoots a ray (blue line), once it hits the screen it refracts in the right direction to show the squinched perspective, which will look normal from the other audience position (The other camera in the image).
However I need to somehow make the green line part of the blue ray so that I can project anything that is in front of the screen, onto the screen itself, the same way anything behind it is shown.

In this image I mixed the refraction with a glossy shader to create a representation of what I'm hoping to achieve, a pretty much need that glossy shader's ray in the opposite direction

I'm using cycles
In the end I need to be able to export a flat image from the curved screen (e.g. by baking), so ideally I'd be able to handle this with a material
In addition to baking, I also need the option to render the screen from the position of a projector (In the example image marked "P")
In this example the screen is curved, but it may have any shape, so a distorted camera frustrum isn't an option.

What I've done so far:

Tried looking for a way to somehow "teleport" the ray back. But it looks like I can only influence its direction.
In the past I've succesfully done this with multiple render passes, where I first render the scene from the position of the audience, and then project it onto the screen, to then capture that from whatever angle I need. This technique however loses a lot of quality as some parts end up being more stretched then others.
Looked into making a custom node using OSL, however the "ray" function doesn't seem to be able to sampling colors.

My thinking is that I should somehow be able send a ray from the audience camera in the direction of the hit position once the camera "P"s ray hits the material, and use the color from that ray to use on the material. But I've been unable to find a way to do something like that.
Any help would be greatly appreciated!

Not very certain of where you're going.  I would consider a render from the position of camera2 (green line cam), with invisible-to-camera blue cube and glossy screen, then bake to UV from projected camera coords.  "succesfully done this...end up being more stretched" I would examine this more closely to figure out why its right, but distorted (triangulation?)

By the stretched I mean that depending on the angle some sections will have gotten more samples then others. So the resolution is uneven. You can try to fight this by increasing the resolution. However, I figured there must be a better way of doing it without losing quality by sampling from the green camera's render output. The blue cube in the last image isn't meant to be a reflection, but rather a projection of what that cube looks like from the angle of the green camera

In the past I've succesfully done this with multiple render passes, where I first render the scene from the position of the audience, and then project it onto the screen, to then capture that from whatever angle I need.

This technique seems to be the most viable to me. If you want to project what the audience is seeing onto the surface, this approach does exactly that - and the simplest solution is often the best.

This technique however loses a lot of quality as some parts end up being more stretched then others.

You can increase the resolution until it satisfies your needs. Yes, you might "waste" some pixels, but that doesn't seem like a critical issue.

A way to somehow "teleport" the ray back. But it looks like I can only influence its direction.

Yeah, I don't think Cycles is designed for custom ray transformations such as the one you describe. This is likely not a common use case, and there is a flexibility-performance trade-off when designing renderers.
Edit: alternative suggestion
Since you have already gotten the projection to work for objects behind the "screen", I can suggest scaling the screen down towards the audience - so that everything, including the cube, is behind the screen. Then you would also need to adjust the camera, and the projection would appear as you intend.

If you need to render the rest of the scene as well, you could combine that render with the rest of the scene during compositing.

I love the alternative suggestion, great thinking! This will require some drivers/code to do this dynamically with a moving camera, but would offer the cleanest picture without the need for multiple passes.
For anyone trying this solution, the "projector camera" will need to be scaled along with the screen for this to work.


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How do i prevent active objects keep moving when they fall down on the passive?
I made a Rigid body scene here and i want my numbers to not keep moving when they fall down on the passive.

Check Enable Deactivation under Physics->Rigid Body Dynamics. For me, the default Linear Vel. and the Angular Vel. worked great.

With the object selected each object must have same properties. So in Physics Tab -> Under Rigid Body Dynamics -> (Tick mark on) Enable Deactivation
To appy all the properties of a single object select all the object you need to move and at last select the object which has the properties enable. In the Tool shelf Physics Tab -> Rigid Body Tools -> Copy from active.
Note : How long the time line is till the object are moving.

I spent much time on Enable Deactivation option but only my objects movement style changed. Did not get the result i want.