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How do I make an object only visible when it is in front of another specific object?
I'm modeling a mouth for a cartoon character, and I want teeth & tongue to be involved. I'm currently working on teeth, but a problem has come up and I'm not sure what to do. I'm trying to make it so the teeth will only be shown when that specific part of the teeth is over the mouth part. Here's a picture:

The light orange is the teeth object, and the dark orange is the mouth object. I don't want the light orange ABOVE the dark orange to be shown, so there isn't teeth above the mouth. I'm pretty sure it has something to do with masks or something. Another note, I am using Cycles to render.

The first pic here shows the teeth object on top of the mouth object. The second picture shows the teeth object UNDER the mouth object. In the second picture, that little white sliver, just above the mouth, is what I do not want to be shown when the teeth object is on top, if that makes any sense. I only want the teeth object to be shown if the part I want to be shown is on top of the mouth.
Thanks in advance.

If your animation style is cartoon then ... you might consider textures.  Perhaps 8 or so mouth textures.  I do not understand all the language above.  Do you think it would be easier to let Blender take care of what is visible and what is not if you place the meshes in their proper location? Can the tongue be moved to location covered by other meshes such as skin?  Suggestion, I think you can provide a better explanatory picture.   Objects can be set to do not render as an animation technique .... yet this seems not the garden variety of mouth.

@atomicbezierslinger What I was trying to say is, I want the teeth to only show if it is over the mouth. So if the teeth object was way above the mouth object, the teeth would not be shown. But if it's halfway, like the picture above, only the bottom half that overlaps with the dark orange wireframe would be shown.

Suggestion.  Better pictures, solid not wireframe, if possible, would help the explanation.  I find the wireframe not enough explanation.  It will be easier when you cooperate with Blender.  In many cases ... the placement of mouth composed of upper lip and lower lip, upper teeth, lower teeth, tongue, cheeks allows Blender to determine the final picture.  If you have a specific artistic style of mouth, please say so. It will be easier for others to help you.  Is there some example face image you can place in the question?

@atomicbezierslinger Okay, I added some pics.

I believe this is impossible to do with materials.  But I was able to get this effect with some render layers and compositing.

First put the front object in a separate layer than the rest of your scene.  Then set up two render layers, one which renders all the layers, and one which excludes the layer with the front object.  (Check out my explanation of excluding layers here).

Next give the back object a different pass index under the Object properties panel > Relations rollout.  And make sure that you have the Object Index, and Z passes enabled on your render layers (see above).

Then use the following node setup to composite the two layers together.

The Less Than node compares the z-depths of the two render layers to find where the animated Suzanne is in front of the other one, the Add and Greater Than nodes work as a logical AND operator between this and the ID mask of the back Suzanne.  So the mix node will grab the "main" render layer iff the animated Suzanne is closer to the camera and overlaps the other one in the rendered image.  Which, I believe, is the effect you desire.


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How can I render with RenderMan in the GPU, in Blender 2.76?
I just find out Pixar made free non-commercial renderer for Blender.
So I downloaded it, installed, added addon into Blender and try to render with it...
tt works really great but.... I don't find out how to change render settings to GPU.
Is it possible to turn on GPU rendering while using Renderman addon for Blender ?
Thank you very much.

Renderman currently doesn't have GPU support:

Does Non-Commercial RenderMan support GPU's?
The current version of Non-Commercial RenderMan is a multi-threaded software application that does not use GPU's due to the current fluidity of graphics hardware and supporting software standards. However GPU's are an important aspect of the future direction of rendering that Pixar is currently researching, some of which has already demonstrated in public. As the technology matures for comprehensive production usage we will reveal more in future.

EDIT For the new Renderman 21, there is a separate Technical FAQ which adds the sentence

For the first time, RenderMan 21 introduces GPU accelerated denoising, and as GPU's mature for comprehensive production usage, we will reveal more in future.

source: Stack Exchange

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

sort: votes


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How to build a Shader for Anodized Aluminium
I have modelled this smart phone based on Iphone 6 reference images. The rendered image of the back of the phone looks like this:

If I look at real life images of this "Iphone 6 Space Gray" I feel that "my phone" misses some fine grain and a "metal sheen". Like these images

My shader looks like this (like suggested here)

I would like to build a shader that gives a realistic look of the apple iPhone space gray material. I also had a look here ... this shader is based on an anisotropic shader which I feel that should be the way to go. It also has the fine grain ... but I don't think it is the solution (and this is also too complicated for me; I would like to understand it). So .. how to build a realistic shader for this apple material ?
Concerning the proposed solutions: I really like the solution suggested by PGmath. When applying his material to my iPhone this is the result.

As I am intrigued by Physically Based shaders I picked up the suggestion of Paul Brachmann and proposed a PBS based solution using the work of PGmath

With all shaders you should consider lighting the scene to match your reference objects, or else you will never get satisfying results. How materials / shaders look is as much about lighting as it is about the parameters of the shadertree. See this talk (relevant) https://www.youtube.com/watch?v=szP24pIqDn8

get your lighting more elaborate first, and you will notice big differences to how the shader parameters behave.

I will certainly watch that video. I can see that there is an interaction between shading/texturing and setting up your scene / lighting, but in your work flow you would do modelling first, then shading / texturing and then lighting is not it ? I would think you first have your basic shading/texturing and you fine-tune that depending on your lighting ?

Think of this... You can set up lights and have weak uninteresting shaders, but you can't have weak lighting and good shader responses. It's a bit of parallelism.

and by weak I don't mean low strength, i mean optimal positioning for the surfaces to pop out.

related: http://blender.stackexchange.com/questions/42133/realistic-aluminum-material-in-cycles

remove the the layer weight, decrease the factor of the first mix shader, increase the roughness of the glossy shader..that may work.

You should avoid plugging a colour output (yellow) into a shader input (green). The colour needs to go via a shader, like a diffuse or glossy.

@cegaton yes, I know that post. In my question I refer to that post. For me there are two issues with that shader: first I don't know how to "tweak" it for Anodized Aluminium (the Apple material) and that is mainly because of the complexity of that shader (I am a beginner)

@PGmath I have referred to this post you answered. Maybe you like to have a look at my question ?

First off, @RayMairlot is right, the image texture (color datatype) being plugged directly into the shader socket (BSDF datatype) does nothing.  Second, lighting is definitely key to making any shader look good, I usually use some variation of this lighting setup for example renders.  I'll have to play around with some shaders before I recommend anything more material-wise though.

RayMairlot: thanks for feedback !! In this case my error did not have much impact since the Image Texture contained the Apple logo and I don't think that has an impact on the desired shader. But I will never connect yellow sockets to green sockets again !! I will edit my question and correct my error

Related: https://www.youtube.com/watch?v=JYuTCJjPTQU (iPhone Modelling Tutorial by Steve Lund - Part 2 with texturing/materials will come soon)

Here's what I have come up with.

The shader consists of a little bit of diffuse mixed into some fairly rough gloss, with a smoother Fresnel gloss mixed in at the end.  I also noticed that the gloss on you reference image has a very slight, yet distinct, variation in reflectance across the phone.  To simulate this I added a noise texture controlling the roughness of the two glossy shaders.
Here is my node layout:

Click to enlarge.
A few notes:

I am using Geometry > Position as mapping coordinates for the noise texture to get even scaling.  Using generated coordinates on an object with a non-cuboidal bounding box results in stretching.
I use an RGB Curves node to bump up the contrast.
All the math nodes just remap the [0,1] range of the texture to the desired ranges for the glossy roughnesses.
The colors in the above node layout are for the gold shader on the right of the render.  The silver one just uses grey in all 3 shaders (light grey for the glosses and slightly darker for the diffuse).

in Europe it is bedtime now (at least for me). But I want to thank you for your work and have a good look at it in next couple of days and then come back to you. For now ... I guess the RGB curve is for adding contrast ? But what is exactly the function of the multiply and add nodes ?

I also guess you are more in favour of Fresnel (vs Layer Weight) ?

@JanScherders  Layer weight gives a linear gradient [0,1) from facing straight on to grazing angles, Fresnel gives a curve gradient defined by the Fresnel function which is more physically accurate.  However sometimes I will connect a layer weight node to an RGB curves node to define my own falloff curve if I feel that Fresnel isn't giving me the look I want.

@JanScherders (first comment)  Yes, the RGB curves is to add contrast.  The multiply and add nodes remap the [0,1] of the texture to the desired range of roughnesses ([0.25,0.30] for the main gloss and [0.02,0.05] for the Fresnel gloss).  It's basically the same thing I did to make a homemade color ramp node here.  Let me know if you want me to explain the math further.

I tried to work with your shader but I guess there is something wrong with my mesh. I uploaded the blend file. I really hope I have not done all this work for nothing ...

@JanScherders  It looks like the scale of your scene is different than mine, increase the scale on the noise texture.

Let us continue this discussion in chat.

In your latest render you used scale = 1800 ?

@JanScherders Yep.

hi, I rendered at 750 samples and when I looked the image at 100% I still saw some "freckles". Therefore I raised the scale to 3600 and rendered again. Would you mind having a look at my image at 100% ? It is here https://www.dropbox.com/s/toyn7t36mrnwc1e/iphone6-back-20151215.png?dl=0 ... as I am not used to the noise reduction node effects i am not sure when the outcome is OK. Or would you say the outcome was already ok at scale = 1800 (rendered at 750 samples) ?

hope you don't mind asking ? I just don't know what is "normal" when to judge a the effect of a noise texture at 100% image resolution

@JanScherders Sorry, I'm not quite sure what you mean.  My general rule is if it looks good keep it, if it doesn't tweak it. :)  (BTW, I think your render looks pretty good.)

@JanScherders  BTW I don't know if you were planning on doing so, but you have to manually award a bounty before it runs out.

I throught I already did ? But did I do it now (award the bounty to your answer) ?

@JanScherders Yes, thanks!  (It doesn't automatically award when you accept an answer.)

Thanks for letting me know. I would feel bad when this bounty was not awarded to your answer (and most helpful coaching in the chat) !!

I came up with this physically based shader:

Basic Setup (including custom pbr node groups):

I hope you can use it as a starting point for your final shader.
But of course it largely depends on your lighting situation how the shader actually will look (although pbr certainly helps).

you mean based on these shaders ? https://www.youtube.com/playlist?list=PLlH00768JwqG4__RRtKACofTztc0Owys8 Would be great to have some good discussions here on these shaders !!!

PBR (physically based rendering) is a concept of creating shaders that actually (more or less accurately) represent the real physical properties of a surface. Therefore physically based shaders are said to look more realistic in the majority of usage cases. And yes, Cynicat Pro really did a great job explaining them.

where can I find some more good concepts and explanations on PBR ?

The theory is explained quite well here: https://www.marmoset.co/toolbag/learn/pbr-theory
But the question is whether you as an artist really need to know about all of the technical background (and regarding the actual implementation & usage in Blender Cynicat is by far the best resource I have found so far).

sometimes you ask A) and learn B) in addition ;) so ... why do you use those "grid" lights and not an emission plane ? And I learned that you can set the light at 5500K :) ...how do you set up those grid lights ? I have seen the node editor but could you explain ?

why do you mix those PBR shaders ?

I am mixing two metal pbr shaders with different roughnesses using a noise texture in order to get that "grainy" look you requested.

Please try to avoid answering a question by just providing some node groups in a blend file.  You should be able to understand everything you need to to answer the question by just reading an answer.  Try explaining how those node groups work and why you should use them that way.  Thanks!

Maybe a bit stupid to answer my own question but both the answers of PGmath and Paul Brachmann have made me try to work out a third option. Recently I watched these videos of Physically Based Shading and I rebuild the Metallics shader explained in this tutorial. Now as suggested by Paul Brachmann I have added the noise texture node to this shader. For this I used the work of PGmath as explained in his answer. This is the resulting "PBS Anodized Aliminium Shader". I hope I have understood the PGmath shader correctly and rebuild the Metallics shader correctly.

Anyway this is the result of the render (using the test setup of PGmath). The silver object has the PBS shader, the gold object the PGmath shader.

@Mentalist hi, in another comment you motivated me to have a look at PBS. Maybe you like to have a look at this question ?

@PGmath here I have used the PBS shader :)

Answering your own question is perfectly fine when you figured out some more details woth sharing as you did. Thanks.

it is not stupid at all to answer you own question. SE not only allows it, but encourages it. Self answers are a great way to share your knowledge.

Hi! Sorry I didn't notice your callout to me in the comment back then. I just happened upon it today and it got me thinking because since the release of the Principled BSDF it's so much easier. It seems you got the result you wanted and it's looking nice. If you are curious what I would do presently, here's a .blend where I'm using Principled but with very fine Voronoi to control roughness. If you zoom in closely you can see the texture.

I stumbled on this old thread when reading about anodized aluminium.
Am I completely on the wrong track by saying that the recently (2016?) introduced Anisotropic shader does exactly what the shader by @PGmatch does above?
(And by extension also the principled shader, if used mostly for it's anisotropic slider?)
In the screenshot below I just downloaded @PGmaths blender file, added a HDR texture instead of the lights and duplicated one of the cubes with a simple Principled shader?

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

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


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Black Texture when baking Ambient Occlusion with Blender internals?
In my blender file, I have a simple castle in which when I try baking the Ambient Occlusion it generated a black texture. How can I get Blender to bake correctly instead of this black texture?
I been reading on forums about this problem which mentioned about inverted normals but my normals or overlapping UV but I generated another without overlapping UV's and received the same problem. They also being negatively scaled but this model has positive scales ;(
Thanks in advance!
Blender file attached here:

I should be something related to the file itself: importing all the objects in a new file allows a correct baking. Is it the same for you too?

Sorry for the late reply but yes I resorted to doing that afterwards. There's no problem when I export the mesh and reimport it into a new file but I wanted to know why it happened so I could prevent this from happening again :P

try doing ctrl + n in edit mode and then try again.

Try to set Environment Lighting to 1.0 in the World tab.
I have tested it now and it bakes AO correctly then.
The funny thing is that you dont need to check the Environment Lighting checkbox and it still makes the change.

I had one part of a mesh acting this way and fixed it by recalculating the normals.

i also have the same issue and tried everything at the end i find out that i am using a duplicate mesh of model for baking purpose but the original mesh was also at the same position but is hidden which is causing artefact in AO maps ,,, so try disabling any mesh having same position as the object whose occlusion you are baking.(problem hidden meshes)

I found that my selection of the baking options was the problem.
Initially I unticked everything except "Ambient Occlusion" (following a few online videos) - this left the primary baking type to "Combined", with direct and indirect light and Ambient Occlusion ticked.
Black bake.
I bounced around online for a while before going in to look at the settings again - the direct/indirect light checkboxes bugged me because I was pretty sure there were no such things in my scene, (just my model) so I decided to click on 'combined' to see what other options there were - and then I found an Ambient Occlusion bake TYPE.
When I changed the baking type to "Ambient Occlusion", direct/indirect light (and the other options) disappeared - then it worked.
I'm guessing the direct/indirect light options in combined when I didn't actually have any lights in my scene were why it was baking black - I'm assuming the bake-type "Ambient Occlusion" option ignores lighting, or provides it's own generic ambient light for processing....either way, that's what worked for me...
JS

I got black AO. Turns out it was caused by the wrong Cycles rendering device,
which I had set to GPU (of course). But I remembered that baking only works with CPU.
So make sure to set the rendering device to CPU.

Had the same issue, also discovered that the Physical Starlight and Atmosphere addon have to be turned off for the render passes to work propperly, in case that people having the same issue and add on c


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Display text on screen - relative to launched command?
I was thinking yesterday that it might be useful to see some text displayed somewhere on the screen when you execute certain commands in Blender. For example if you enter "Keep Uv and edit mesh mode selection in sync" mode Blender could display a text that says "Sync Mode - On" on your screen, have anyone seen any script that has this function? Is this day dreaming on my part or is it possible?

In the past there was a screen cast add on.
Here is some history.
http://www.blendernation.com/2014/07/02/screencast-keys-addon-is-removed-b3d/
The info window type shows user operations.  The default vertical size of the window was increased to see the contents.

Python Script Software writers find this useful.


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How do I use the inpaint node?
Upon reading this post the inpaint node is mentioned.
The manual for this node is still on the "to do" list...
So, What is the purpose of this node and how do I use it?

see: http://lists.blender.org/pipermail/bf-committers/2012-July/037357.html  and http://blenderartists.org/forum/showthread.php?260885-Blender-to-get-Inpainting-node!-Awesomeness

The Inpaint node will extend the borders in an image into transparent or masked regions. The distance setting determines how far the edges will be extended into the transparent region.
For example, in the image that follows, the background is transparent being generated by masking out a cube.

The compositor was setup to use an Inpaint node to generate this image with the image extended into the transparent region by a distance of 100.

The compositor setup is shown below:

This is useful for pixelation (referenced postreferenced post) and cleaning up edges when post processing images.

The blend file used for this example is at

InPainting is provided to solve problems like "wire removal" and holes created during chroma-keying as shown in the image here. To make this example clearer, I've used a fake wire (and a fake object) but in reality you'd normally use fine, chroma-keyed wires. This isn't the only way to remove wires of course, but it's a simple one.
You can use motion tracking to do the same thing - the point is when the wire has been removed you're left with a small hole in your frame. For a single image this isn't that much of an issue and could be filled in with Photoshop (later versions have InPainting as part of the healing brush), GIMP, Krita etc.
However, if this is a video you've got 24 - 30 frames for every second of footage and that's a lot of painting. As InPainting is done in the compositor, you don't have to worry, even for long sequences.
In the left image shows the "wire" in place and after chroma-key has been applied you'll see you're left with a blank space - it's shown as a black line here but it will be alpha in your blender output.
InPainting fills in a couple of pixels using the surrounding "background" and voila, your wire is removed. Note that the wider your "hole" is, the more noticeable this effect is! If you use more than a few pixels of infill, the effect is almost as irritating as the wire and your viewers won't be impressed.
As part of this demonstration I've left a little of the chroma effect visible so you can see there's no cheating. Normally, you'd look to get a perfect key.
Inpainting can also cover up a multitude of other minor sins such as control points for motion capture: use it sparingly and it will amaze.


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Cause of Frayed Edges
I am working on a computer tablet. Attached the screen shots of edit mode and object mode of the "to be" screen of this computer tablet. What is causing these frayed edges and how to solve that ?

It's because the topology isn't the way you think it is. From the menu in Edit Mode, Select > Non-Manifold and Blender will show you where there are problems. Then zoom in and look closely at what's happening. These sorts of artifacts can occur if you fill edges or faces in with the wrong part of your geometry selected and don't notice it at the time.

Thanks !! Is it possible to "remove" the non-manifold stuff and repair the mesh or is that too difficult ?Non-Manifold are faces that don't have 4 vertices ?

fix these two faces that are making a mess out of your geometry: http://i.stack.imgur.com/uNUBF.png and http://i.stack.imgur.com/tnCV5.png

Jan, if you use the key sequence Mentalist supplied in his comment (Select > Non-Manifold), and switch to face select mode, the first step is  to delete "Just faces" to clean up the mesh. Then it may be necessary to clean up a non manifold edges, too, using delete "just edges and faces".

There're some faces with twisted vertices the scaled model reveals them:

To fix it remove the faces and recreate them by selecting the edges followed by F.

You might also want to consider to remove the loop cut in the upper part.
Related:

What is non-manifold geometry?
How to create a smooth surface onto a rectangle frame?


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Why can't I see this curve's vertices?
I'm new to Blender and I guess my problem is silly for many users, but anyway...
I must have accidentally changed a setting (via hotkeys) and now, when I create a curve (e.g. a bezier circle) and go to edit mode, I can't see the vertices of the curves. Instead, I see the bezier handles and the normal.

I can't find anything in the menus, searched on the web, tried to restore the settings and even downloaded again the app, but nothing to do.
How can I restore the usual visualization?
Thanx everybody.

This is expected behaviour when you add Bezier circle, you see its control points with handles and normals like TLousky answered. Probably you mean that you'd like to see actual vertices of the mesh; in that case you should convert circle with Alt+C shortcut from Object mode.

Don't know of any shortcut to show and hide curve handles, or a way to turn them off by default in the settings (are you sure you didn't just add a mesh circle until now?).
But you can turn handles on or off through the Properties Panel (N) > Curve Display > Handle.

By the way, just for a bit of terminology and trivia:
These points on bezier curves are called Control Points, rather than Vertices (which are mesh points).


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Why is Blender rendering the wrong resolution?
I configured the output for 1080x1920, but it's rendering 1822x1922, so I can't append the video intro to the videos using Avidemux (Avidemux requires the videos to be of the same resolution). Why is this happening to me? How can I fix it?

Try to use a different Codec. Are single images rendered correctly? (F12)

I tried using "JPEG Avi". It says "resolution: 1088x1920" and "show resoluyion: 1080x1920". I could not understand what F12 did, I saw no new image file.

You need to change the render type to image to have one saved or when you have this single image not being rendered in background you can save it manually after having it displayed. It should be displayed after hitting F12.

Make sure the dial below the resolution fields is at 100%.

Also check your aspect ratio to X=1:Y=1 , it's just below the resolution number field shown on the image above.

It is. But when I render the video, open in VLC and show information about the media, it says:
*resolution: 1088x1922
*show resolution: 1080x1920

VLC might be at fault. I'm seeing exactly the same resolution as Anders, but another video player, djv_view reports 1080x1920


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Animate the rotation of a shotgun barrel
How can I rotate the barrel like so, in the first image below?

I want the barrel to rotate 45° so that the shotgun shells can be put into the barrel. But when I rotate, I get this image below:

See if this solves your problem.

You have 2 objects selected with different origins.  You probably want both objects to have the same origin so they rotate about the same point, or parent one object to the other and rotate just the parent.

Thats because the "Origin" of the barrel is all the way to the right of the screen. Every object has an "Origin" and it is the yellow dot that appears every time you select an object.
Here is a tutorial to explain what an origin is and how to change it. - https://www.youtube.com/watch?v=0FxrRdbk854

Thanks, however my rotation is not straight even though I am using R + X (45.0). My rotation curves to the right and falls in place with the desired 45 degree angle, that is straight from the new 3d cursor origin.

use [R + X + X]

I get the same result. I have to change it to R + Y + Y though.

oh ok. So, your problem is fixed now? or is it still now going straight?

No, though the rotation is perfectly straight over the x axis, the barrel is veering to the right as it makes its rotation. Any suggestions?

did you change the origin of the barrel?

Oh I see. The animation keyframes must be the problem. Change the last keyframe is probably the problem since the barrel might be veering to the right on that.

The objects have different rotation paths when I select them all and hit R + X + X
Is there a way I can combine all objects using join and still have the barrel pivot over the x axis?

If you join the meshes, you would be able to do what you want to do, but that is more complex as it would require "bones".

@nmm131 Try changing the view from Perspective to Ortho view by pressing the "5" key. You can switch from Front, Side and top views by pressing "1" "3" and "7" keys.

If you want to avoid using bones, and only animate the rotation, then I would use the 3d cursor as your pivot point.

well, it's a bit strange because he'd have to move the cursor back into location whenever he does this

When I play my animation from that originates from blender, the barrel animates backwards in the opposite direction. It still slides to the right then slides back to the left when making the 45 degree rotation animation though. I have tried all tricks above. It also rotates up instead of down.

This answer is guessing your barrel was once the same object as the stock, and you separated them. If not, I'm sorry I could not be of a help.
When creating a object, an origin point is made in the center (usually) and if you were to go into Edit mode and work away, as you have, then at one point decide to CtrlP to separate the two objects (in this case, your barrel and the stock) later on in your model, then your separated object will have the same origin as the other.
Causing it to rotate at the wrong position.
I may of said that too confusingly, so I'll just say the solution now.
First, I created a very bad remake of your model, as it's currently 5:02 AM.
It took me 3 objects to spawn in, a cube, and 2 cylinders. I shift clicked the two cylinders and held CtrlP to separate them into two objects.
At this point, I have what I believe is your current situation. To fix this, I selected the back faces of the barrel, and pressed ShiftS and set my 3D cursor to the median point of the selected faces. (cursor to selected) I then entered Object mode and pressed ShiftAltCtrlC and selected Origin to 3D Cursor
The barrel now rotates from there.
This is perhaps unhelpful, and I'm sorry if this is unclear or such. I shall add a gif tomorrow explaining the process. hope as someone could edit this for me, as I must sleep. Good luck in your efforts!

@Gwenn Centre is the british english way of spelling center. Was no need to edit it, IMO. :)


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How To Make Two Objects into One Mesh and then Only Animate One Object (Rotation)
I have two obejcts, one of which I want to rotate 45 degrees then bring it back to its original rotation, while the other object stays in its place.

I am having problems animating both meshes and combining it into one event in another source because when I import the two animations, the animation of the object that should be rotated is acting in weird ways in relation to the static object. I'm hoping by combining them to one object, its rotation will hold true to how it is showed inside Blender when I hit play.

I'm going to say that your importer or exporter is defective.  I am also not optimistic that unifying the mesh will solve things since it actually complicates things.
If you want to have a single mesh where part of it is animated, the first thing that comes to my mind is an armature paired with vertex groups.
You will need to assign all the vertices of the moving part of the mesh to a vertex group.  Select the mesh.  Enter edit mode.  Select the vertices for the animated part.  In the Mesh/ObjectData panel use the Vertex Group subpanel + button to create a new vertex group.  Then use the Assign button to add all those vertices to the group.  Double check that the weight is 1.0 (sometimes it is 0.0, which is almost useless).
Go back to Object mode and add a new Armature.  By default its single bone will be named "Bone".  Switch to edit mode, select the bone, and go to the Bone/ObjectData panel and rename it to match the vertex group of the mesh (which is probably named "Group").
Go back to Object mode.  Select the mesh.  Go to the Modifiers panel and add an Armature modifier (under the Deform section).  Choose the Armature as the modifier's object.  Make sure the Vertex Groups is checked.
Now you can select the armature and go into Pose mode (usually Ctrl-Tab) and put some keyframes on the bone to animate it rotating.
Because the bone and the vertex groups have matching names, the armature modifier will make the object deform according to the motions of the bone.
As you can see, this rig is much more complicated than two objects, one of which is animated.  If your importer/exporter malfunctions on your current project, I have doubts that it will properly support the intricacies of armatures.

Ok thank you, I will try this and report back. I'm assuming blender has malfunctioned somehow since exporting these animations and implementing them elsewhere never had these animation problems. I will try vertex groups to armature for the two sections and see if that helps. I appreciate it!


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N Panel (Location & Rotation Boxes are YELLOW) ... Makes my Mesh Load up in the Blend file in a new location with different scale
I have this mesh inside my blend file. Whenever I load this/open this blend in Blender, the mesh appears in a new location as opposed to how I saved it. The only thing I see is that the boxes in the panels are yellow as opposed to normal color. How can I change this so that this mesh appears with its same scale and location when I open the blend file?

XD you animated the mesh. The boxes turn yellow when you animated something. Do you see that yellow line in the Timeline? That means that you animated the mesh to a new location from Frame 1, all the way to the yellow line!
Delete animation of object
Here is how to get rid of the yellow line, which would get rid of the animation. :D

Ahhhh thank you! That solved it, I did not recognize that! Good tip!


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Unlinking Objects
I linked a group of objects together so that I can move the whole group of objects together. But now I want to unlink this group of objects.
I did not join the objects but linked them I think. It is not one object but still a group of linked objects. So I don't think Separate will work for this? I think it is Unlinking objects and not Separating Meshes (of one Object)
After reading the comments and answers, PGmath is right, I parented the objects but couldn't remember that I did.

It sounds like you have parented your objects to another object with Ctrl+P.  To unparent an object select it and hit Alt+P.  This will give you 3 choices:

Clear Parent will unconnect the object from all parents it is attached to.  This will also not modify the object's local transformation, i.e. undo all transformations it inherited from its parent[s].
Clear and Keep Transformation does the same thing as Clear Parent, but also changes the object's local transformation to still reflect all transformation inherited from the parent[s], i.e. the object does not move.
Clear Parent Inverse changes the object's parent-space transformation to equal it's local space transformation.  Note: this option does not clear any parenting.

You may have a terminology issue here. "Link" usually refers to placing a copy of an object found in one file in a scene in another file. But if you combined several objects in the same file into a collection that you could treat as one, you may have made them into a group, either from the sub menu of in the fifth panel from the top of the "Object" menu of the footer of the 3D viewport in object mode, or by pressing the key combination CTRL-G? You can remove a single object from the group by selecting the object and pressing the key combination CTRL-ALT-G, and can remove an object from all groups to which it belongs by pressing the key combination SHIFT-CTRL-ALT-G. If you want to remove the group entirely, there is no key combination, but if you have the dynamic spacebar enabled, you can press the spacebar, search for "group", which should show an item containing the entry, "Remove group", or "unlink group".

is this what you want ? just make single user , and check up the object data


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Is there an easy way to make volumetric clouds for Cycles?
I'm working on an animation that takes place on a plane. I'd love to include the big detail of clouds moving past through the windows, but I'm using Cycles. I have no experience with the particle emitter, so the only clouds I've ever created were ones from the add-on for Blender Render only.
I want an easy and fluent way to create a huge sky atmosphere, similar to the one in the SFM Saxxy Awards winner, Turbulence.
So, how do I do this easily in Cycles? I'm not with a team or anything, and I don't have hours of spare time to do this. Again, I have no experience with using the particle system.

Andrew Price has a nice Tutorial about this topic.

Let's use the Cloud Generator addon to make nice clouds and the new Point Density Texture to render them inside Cycles!

First enable the addon in User Preferences under Object: Cloud Generator.
Switch to Blender Render (the addon does not work under Cycles), add some cubes and turn them into clouds with the addon (the UI is located inside Tool Shelf T under Create > CloudGenerator in Object Mode):

(we won't use the explosion because it's not a cloud and requires a different Cycles shader)
After you choose the cloud type it will generate objects like this:

We are interested in the CloudBounds object and in CloudPoints.
Switch to Cycles Render and if using pre-2.77 Blender version use CPU rendering (Point Density does work on GPU in 2.77+). We need to give the CloudBounds object a Cycles material:

Play with the Radius and Multiply Node to fine tune the shape and density.
Delete all the non-used objects from the scene and make sure there are no Blender Internal materials left. All the CloudBounds should have Cycles materials and all the CloudPoints should be without material and hidden from render.
Add some lighting: Sun Lamp, Hemi Lights. Render:

When you get the hang of it create any shapes you like from differently sized and deformed cubes or some basic geometry.

The Cloud Generator addon does work with Cycles (using Blender 2.78a), and in fact it creates some sophisticated Cycles node groups. Probably the Cycles support was added since this answer.

Take a cube and subdivide it with Subdivide Smooth using using some random fractal value and some smoothness.

Make the mesh smooth, add a subsurf modifier and create a material that has no surface but volume scatter with some texture controlling the Density:

On a different layer create an object that is very large and add a particle system that has a low number of emissions, no physics and that uses the cloud object as the render object and has the emitter disabled.
For variety create a few objects with different shapes and textures and use them is other particles systems.

How do you get rid of the rectangular prism that contains the particle modifier, as hiding it also hides the particles


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How do you use the Boolean modifier without horribly deforming the mesh?

I'm currently modeling a plane where the exterior was modeled first and the interior was added in with Ctrl + J as a separate object, so the plane as a whole is non manifold.
Here's the interior of the first class room:

This is in-between the interior and exterior (not connected):

So, as you can imagine, I'm trying to cut a porthole into the plane with the porthole object. This is the boolean modifier on the plane (raising the modifier any higher deforms the plane):

Rather than getting a nice clean cut, I got this:

The interior part was cut through, but not the exterior. I find this extremely confusing, because it should have worked in theory. This is what the wireframe looked like before the modifier was applied:

In the image, the porthole object was selected, so in the plane mesh you could see 2 definite cuts. So how can I get it perfectly, just like the wireframe "preview"?
I thank you in advance for helping.

I avoid using the boolean mod for just this reason. bad mesh is always going to be there. try manually modelling the windows, it shouldn't be too hard.

True story. Google for "blender how to make holes", you'll find better solutions. Boolean is completely useless in my opinion.

In situations like this, the problem is rarely the Boolean modifier, but rather the underlying geometry. If you want some kind of answer for your scenario it's more helpful to us to see the .blend you are using. upload here, you can always delete it later but -- at least we'll know if there's some solution.

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


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Texture Coordinate vs Geometry Node
When working with generated texture coordinates I see sometimes the Texture Coordinate (generated) and sometimes the Geometry (Position) node used. What is exactly the difference ?

Geometry position is almost certainly the (X,Y,Z) coordinate of the surface (or interior) point that is to be coloured/textured etc. as part of the render.  Texture Coordinate defines what is to be used for the (U,V) coordinate used to lookup a position on the UV Map and use the pixel information found at that point as the source for the rendered pixel (or the onward journey through node graph).
link

The Generated and Position outputs each represent coordinate systems.  These are often used as texture coordinates for procedural textures since they are 3-dimensional, though they can be useful for other effects as well.

Generated Texture Coordinates
Generated coordinates are defined by the bounding box of an object, and are unique to each object.
Generated texture coordinates give the bounding-box-space position across the mesh.  The bottom, left, front of the bounding box is the origin (coordinates [0, 0, 0]), and the top, right, back of the bounding box is [1, 1, 1].

I use generated coordinates when I need the texturing to transform, particularly rotate, with the object.  However when the bounding box is significantly non-cuboidal generated textures will stretch and distort the texturing.  In these cases you may need to manually "un-stretch" the texture with a mapping node, or use Position coordinates.
Generated coordinates can also be useful for non-texturing methods, like creating gradients or other more advanced techniques.

Position Coordinates
The Geometry > Position output gives the position in world-space across the object.  The origin ([0, 0, 0]) is the world origin and all other points are simply their respective position in Blender Units relative to the origin.

I like to use Position coordinates to keep uniform texture scaling across with a material assigned to multiple objects with different sized bounding boxes.  Using Position coordinates also prevents distorted stretching on objects with significantly non-cuboidal bounding boxes.

I would say it does not matter too much in practical situations to use the one or the other. Or are there situations that it matters which node you use ?

@JanScherders  See edit.


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Dissolve or disintegrate part of mesh while it is animating?
Is it possible to dissolve each vertice of a part of a mesh while it is on the course of its own animation?
I.E have an animation for the mesh and have an animation for the disintegration and have the disintegration say remove half of the mesh while it is animating on its other animation (the transformation, rotation, scaling of its other animation that is not disintegration)?
Then I can make multiple disintegration animations, say 4 total and each will disintegrate 1/4th of the whole mesh, and play all 4 at the same time of its other animation to see the whole mesh, not just part, disintegrate while the single mesh is moving over the course of its animation?
Basically dissolve the mesh without having it jump to some pose before it can dissolve. I.e. it can be in any animation pose when it can start dissolving.

I think you are looking for the Build modifier.
The build modifier erases your mesh, then animates it being "re-built" face-by-face.  Just add a Build modifier to your object, set the Start frame and frame Duration to the desired amounts.  Then check Reversed to have it progressively take away geometry instead of building it from empty.

To get a more dissolve-like effect I would also check Randomize, this makes it randomly choose faces to take away, instead of sequentially doing connected adjacent faces.  Here is a side by side comparison, with Randomize checked on the left and unchecked on the right.

How can I have this start at any time during an animation that does not have any dissolve modifier?
i.e. say a player mesh is going about its idle_walk_run cycle. It will have its bones in different relative locations
but when a button is pressed all players are forced to run this dissolve animation (they all have the same skeleton) no matter where they are in the idle_walk_run cycle.
so some will dissolve from idle position, some will dissolve with their legs out in front of them as they are walking, or some in a full sprint?

is this possible? I have seen in a game such as Halo where someone is shot with a laser, no matter how the ragdoll is posed on hit impact of the laser (instant death), only then will the dissolve start at all bone locations

@nmm131  You mean you want to do this in the game engine?  (You didn't mention that in your question.)  The animation position doesn't matter though, just put the Build modifier after the Armature modifier.

I will compile everything in a game engine. But how would I trigger the build and re-build modifier for a mesh that is in animation?
do I bake the build as a material and then apply the material to the mesh object? or is there a way to conduct this with a linear plane or sphere that would overlap the mesh to induce the dissolve?

@nmm131 I don't know, I'm not a BGE expert.  I'd ask that as a separate question.

If you want to have a truly powerful control over your animation and manipulate your mesh, there is a bit cumbersome, but well-suited approach to this: Shape Keys.
Check this out: https://www.blender.org/manual/animation/shape_keys.html?highlight=shape%20keys


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Displacement Modifier and Texture Coordinates
I am using a Displacement Modifier with an Image Texture.
Now in the Displacement Modifier panel you can chose the Texture Coordinates. On this page http://wiki.blender.org/index.php/Doc:2.4/Manual/Modifiers/Deform/Displace I read that "Global – take the texture coordinates from the global coordinate system" and
"Local – take the texture coordinates from the object’s local coordinate system". First, I don't understand what is meant with a local and global coordinate system but I guess since I am using a Texture Coordinate (generated) that I should chose LOCAL ??

Do yourself a favor and use the newer manual: https://www.blender.org/manual/modeling/modifiers/deform/displace.html?highlight=displace   the one for version 2.4 is quite old and might not reflect the way newer versions of blender work.

related: http://wiki.blender.org/index.php/User:Rking/Doc:2.6/Manual/3D_interaction/Transform_Control/Transform_Orientations

Local is when you are using the object's own XYZ coordinates, regardless of it's placement in the global coordinates. For example, When you rotate an object in object mode the object will no longer be aligned with the world

Global has to do with the XYZ grid that starts in the origin 0,0,0. The transformations occur using the world's coordinates.
Here's a small example of how If your object is not aligned with the global coordinates you'll get different results using the displace modifier:

ok. So I guess I have to use the global coordinates.


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Generated texture coordinates vs Unwrapped texture coordinates
If you want to map an equirectangular image texture to a sphere - like a map of the earth to a sphere - is there any necessity to use an UV map ? Or can I simply use the generated texture coordinates ? In general, when do you choose for UV unwrapping and when to use generated texture coordinates ?
I don't think this question is a duplicate with this question because these answers all start with the uv unwrapping method and I want to know if UV unwrapping or generated texture coordinates works best for my specific question.
And I also would like to learn some general guidelines when choosing uv unwrapped vs generated texture coordinates

related: http://blender.stackexchange.com/questions/3315/how-to-get-perfect-uv-sphere-mercator-projection

I still don't agree that this question is a duplicate. I don't ask what is the best way to unwrap a sphere but I ask what is the best way to map an image texture to a sphere ... Please explain why my question is a duplicate

I agree that this is most certainly not a dupe.  This question merely uses a sphere as an incidental example and is not asking about the best way to unwrap a sphere; rather about pros and cons and use cases of generated vs. UV coords.

@JanScherders Since you've asked how texturing a sphere, it's a dupe (IMO). When you really think about it there must be a reason why the answers starting with uv unwrapping, BTW: answers have nothing to do with questions. If the answers of the found questions doesn't solve your issue why not simply write: "Based on this question i'd like to know..." instead of "This is not a dupe" - this is less offensive and better practice (IMO). Also duplicates are not bad, they are helping future visitos to find the correct answer. Anyway, don't take it personal.

@poor Thanks for your feedback. I still have to get used to the idea that duplicates are not bad. Everytime when someone tells me I added a duplicate I feel like I have done something wrong. And I will certainly try to improve my language. Thanks, poor !!

@JanScherders  Though I still didn't agree that this was a dupe, poor is right that dupes aren't bad at all, especially considering that SE's search functionality leaves a lot to be desired.  (Ironically missing link to meta post I couldn't find about how dupes aren't bad.)

UV Unwrapping
The one major benefit of UV unwrapping an object is that it gives you exact control over the texture placement.  Usually you would unwrap geometrically complex objects, or objects which you would like to do texture painting or add decals to.
However, UV mapping has two major pitfalls.

Seams.  By unwrapping an object you are basically cutting it up with seams and flattening it out to place a 2D texture on it.  The obvious problem is that these seams create undesirable "cuts" in the texturing.  So care must be taken to place seams where they are least visible.

Distortion.  Due to the nature of UV unwrapping, by cutting a 3D object up and plastering it flat there will be some distortion of the geometry.  If done well this can be minimized fairly well, but that often requires more seams.  So when UV unwrapping an object you need to find a balance between more seams and more distortion.

Usually the benefit of having complete control over the final output (which is often absolutely necessary for complex models and custom texturing) outweighs these cons.  In such cases the above problems can usually be sufficiently mitigated.

Generated Coordinates
The key to generated coordinates is that they are 3-dimensional.  This is both their biggest advantage and disadvantage.  Being 3-dimensional makes them perfect for procedural textures and voxels (though position coordinates work just peachy too).  However, being 3-dimensional also means it is often tough and/or not ideal to use generated coordinates with 2-D image textures.
There are a few ways of using generated coordinates for 2-D textures, through using different mapping projections or some more advanced vector wrangling.

Each situation really determines what you should do.

In general

Using generated coordinates gives you less control, but is easier.
Using UV's is more precise, but harder, especially on complex meshes.

Now, I will use an example scene, to show some of the differences.
In this example, we will use:

Sphere one uses generated texture coordinates
Sphere two uses sphere projection, to create a UV map.

In this circumstance, I like the results of sphere 1 better than that of sphere 2.

When using generated texture coordinates, keep in mind what mode of texture projection you are using. I have a sphere, so I am using sphere projection. For other objects with complex meshes that you do not want to unwrap, box projection is usually a good option.
When looking at the UV map that was created through sphere projection on sphere two, you may notice that the unwrap is not perfect, and that is one of the advantages of using generated texture coordinates.

Also, remember that using UV or generated texture coordinates are not the only options. Using object coordinates can come in useful when you want the texture's projection to change based on the position of the object, such as when creating roof tiles. You may use a cracked texture, and want the cracks to be in a different place per tile.

So when deciding, just think about what your goals are, and what the easiest way to get there is. In the earth model case, I would use generated coordinates with sphere texture projection.


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Geometry node as input for Fresnel node
If I use the Geometry node as an input for Fresnel, which attribute of the Geometry node do I connect to the Fresnel node (and why) ? Below an image of the node tree that I am building

What are you trying to do? That will determine what to plug and how to plug it! If you are trying to build a PBR Fresnel then first watch Cynicat's videos on Youtube, it's a nice introduction.

I have a sun shining on a sphere (planet earth) and want to have realistic reflections and I thought that i can do that best with connecting the Geometry Node to the Fresnel node and that connecting to a mix node. I will edit my question and add an image of the node tree

Why are you using Position as Mapping coordinates? That results in your texture not moving with your object.. Everything else is OK. You don't have to put anything into the Fresnel Normal input, Blender will use the object's normals by default.

@Jerryno In this question http://blender.stackexchange.com/questions/45199/generated-texture-coordinates-vs-unwrapped-texture-coordinates?noredirect=1#comment76378_45199 I asked how best to map my image textures to a sphere. I also asked this question http://blender.stackexchange.com/questions/45148/texture-coordinate-vs-geometry-node/45149?noredirect=1#comment76202_45149 That is why I use the Position for mapping coordinates. Why is my texture not moving with my object ?

@Jerryno ... so the connection between the Geometry node and Fresnel node is not necessary because Blender will use the normals by default ? Thanks.

I don't mind you explaining a few things in chat :)

Yes the connection is not necessary blender will use normals by default. I don't think you understand how mapping vectors work, you don't want to use the position output but generated texture coordinates. There should be multiple questions and answers on this site discussing this in detail.

I asked a couple of days a question about Geometry and Texture Coordinates but perhaps I still don't understand it ... It was my understanding that a Geometry node can be used for generated texture coordinates ....

@PGmath could you perhaps shed some light on the above issue of (in)correctly using Position for generated texture coordinates ?

It is well documented here how the outputs differ: http://blender.stackexchange.com/a/45149/7777. What you don't understand is what effect will those mappings have on a texture.

@Jerryno I hope you don't mind that I come back one last time. Do you mean the sentence "I use generated coordinates when I need the texturing to transform, particularly rotate, with the object." ?? Or where do you think I don't understand ?

Yes, you use generated texture coordinates when you need the texturing to transform with the object. So why you are not using them?

OK. you mean that when I want to rotate the earth I better use Texture Coordinates ? If that is your point I understand and I will replace the Position by Texture Coordinates. Many thanks for the lesson !!


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Mapping two image texture on a sphere
Some months ago I watched this video of Blenderguru about "How to create a realistic earth in blender". In this video blender render is used and
now that I understand texturing in cycles a little better I am trying to rebuild this "realistic earth" with cycles.

In the video - starting at about 11:30 min - it is shown how to map the "earth day" and "earth night" image textures. Depending on the lights shining on the earth the earth or night image is projected. I tried to rebuild that in cycles but I think I a making mistakes. In the circled box the "night" nodes are found. What Is my mistake ?
P.S When you see other mistakes in this node tree, please let me know.
OK ... I now have implemented the advice of Uncle Snail (except moving the black slider). Below an image of the earth and the updated node tree (I also rearranged nodes for better overview).

In the Color Ramp, I did not move the slider. Is that really necessary ??

Plug the output from the texture into the color ramp node.
That should do the trick.
Here's how it works.
When you output an image (black and white in this example), the white values stand for 1, and the black values stand for 0.
Therefore, when you plug an image texture that is black and white (like that of the lights, all the white will be 1, and all the black will be 0. In this case, the white is where there are lights, so you want to mix with an emission shader. A value of 1 (white on the texture) will mix completely, and a value of 0 (black) will not have any light.
The color ramp node, is simply for mapping how much of the texture is 1, and how much is 0. When you plug a value it, 1 (white) will be all the way to the right, and 0 all the way to the left. All in between is the values between 1 and 0. If you change the color at the right to grey, all that used to be white (1) will now be grey (0.5).
This way, if you drag the black slider almost right up to the white end, there will be no light until the texture becomes very white.
Here is an illustration.
On the right, the lesser lights are cut out, so just the powerful ones shine through. This is done by the color ramp.

Also check out Gleb's tutorial. It is a good example. Just watch how he uses it.
http://www.creativeshrimp.com/how-to-make-a-spider-web-in-blender.html
In your case, I wouldn't use it, except you may not want there to be as much light, then use it maybe. Just preference.
However, if you look, where there is not light in the texture, it is not completely black, so you may want to turn up the bottom a little bit, to crush all low values to 0. (like this) [example uses white as input for emission, not color as input, making the lights more prominent (which is what I would do when making a globe).]

In the video blender guru first adds another node and connects that to the color ramp. I thought I would simulate that node by adding a Diffuse Node with color white. Are you sure that I should connect the Texture to the Color Ramp ?

I updated my question. In the Color Ramp, I did not move the slider. Is that really necessary ??

Yes! When you take the output from a texture, it is a color, which can be converted to a number. The output from a shader, is like a surface (it's a different output), and is not a color. The only thing you should ever be plugging a shader into is an output (except in advanced situations) (and into mix/add shader) [A shader translates the color into a method for the color to be displayed (shiny or dull), so is only needed for the output].
About the color ramp, no, it is not necessary. (short answer) I will update the question for a longer answer.

I have updated the answer.

Also, you may want to use a color ramp to turn all the places without lights to black, as that texture is not black in those spots (second illustration).


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Black backround after render
I am a begginer in blender and I download the template from this link. If I am render the image i get this. It have got black backround!!!
Please help!
Thanks!

do you want to know how to get a different background?

No. How to render with planet and backround, because I get this: https://www.dropbox.com/s/dt15nmxo7lrpbd6/untitled.png?dl=0

so your problem is that the planet is not rendering. Is the planet visible in the 3D viewport?

Yes! This is my problem :-(

is this your problem?

no. Here is my screen shot https://www.dropbox.com/s/4mwkyq4jtcmu9pi/Screenshot%202016-01-20%2015.59.21.png?dl=0

I think you need to check those toggle buttons in the scene settings. The only one you have checked is 'universal' check the others: 'night' 'shadow' 'atmosphere' 'sun

Not work. Some render...


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Rotating an empty
If I rotate an empty I would expect to see the same rotation on the x,y and z axis for child and parent, but I see the rotation for the empty in the xyz rotation fields but the child xyz rotation fields stay 0,0,0. Is that logical ??

I think you mean "the child xyz rotation fields stay 0,0,0" right?

May I ask why you focus on an empty? Do other objects behave differently? Anyway, here's a related question (about location instead of rotation): Location of object wrong?

Yes, this is exactly what is supposed to happen.
The transform values shown under the Object Properties panel are the local transformations of the object.  All inherited transformation is applied in global space, not local space.  This is why if you un-parent an object it will snap back to it's original location unless you choose to keep transformation.

Matrix Multiplication
Yes its logical because you are seeing factors of a multiplication in the info panels and you see the result visualized in the 3D View.
The final location/rotation/scale of the child is a composite of the parent matrix and the child matrix. The matrices are multiplied in an appropriate fashion.  You see the final result in the 3D View window.  If the parent has uniform scale 8 and the child has uniform scale 2 then the scale result you see in the 3D View window is 16 = 8 * 2.  You see the 8 and 2 in the object rotation info.  You might see some useful information in the dimension info as well.
If you had a chain of parents of length 2 with uniform scales of 5 and 8 with the child of uniform scale 2 you would expect to see a final visualization of 80 = 5 * 8 * 2.  So with more complex chains showing the factors is quite useful and necessary.
Of course I can not do justice to the matrix multiplication math that has been around for quite some time and can occupy a few chapters in a 3D computer graphics book.
A video.  I am just providing a starting point for you in limited time.   I am not trying to promote a particular video. You will decide what entertains you.
https://www.youtube.com/watch?v=PpkTpGH-O40
Wikipedia Reference
I am not stating that what is linked below is trivial reading the first time.  There are some nice pictures in some of the references.
https://en.wikipedia.org/wiki/Rotation_matrix
https://en.wikipedia.org/wiki/Scaling_%28geometry%29
https://en.wikipedia.org/wiki/Translation_%28geometry%29
https://en.wikipedia.org/wiki/Transformation_matrix


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Simulating the atmosphere
Some months ago I watched this video of Blenderguru about "How to create a realistic earth in blender". In this video blender render is used and now that I understand texturing in cycles a little better I am trying to rebuild this "realistic earth" with cycles.

At about 22:00 min Blenderguru starts explaining how to simulate the atmosphere using blender render. The idea is that near the edges the atmosphere gives a bluish tint to the earth. I tried to work this out with the setup as above (same idea as used for a transparent balloon) but blender guru is doing something with fresnel. I think that is a better solution ? How to simulate the atmosphere with fresnel ?

see: https://blender.stackexchange.com/questions/92209/how-to-exponential-fall-off-for-volume-density

I think what you want to do is mix whatever shader you are using for the earth's surface with a bluish shader towards the edges.

To do this just plug both shaders into a mix shader (like you already have), with the bluish atmosphere in the bottom socket.  Then control the mix factor with a Fresnel node.
]

thanks.  In the complete setup I have three spheres ... one for the earth (smallest sphere), one for the clouds and one for the atmosphere (largest sphere). How to implement your node tree with this set up ? What is wrong in my set up ? I mean my node tree also creates that bluish shader towards the edges (like for a balloon). To be honest, I feel it should be something with fresnel, that is why I ask. But what is different in a fresnel setup vs my setup ? Btw, how to create those nice stars ;)

@JanScherders  For yours in particular, if you want to use a Fresnel node, just swap the translucent and transparent shaders and plug the Fresnel into the mix factor.  There's nothing "wrong" with yours per-say, Fresnel is just a different way of doing it.  Try both ways and see which you like the look of better.

it is just that the blender guru solution in blender render looked better ...

after comparing the results of both the Dot Product and Fresnel method I think I prefer the Dot Product result better. I really had not expected that. Anyway, thanks for showing me how to use the Fresnel node here.


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Center objects with particle system
how can i center a group of objects individually in the center of every face of the plane, with a random order in all over the plane, with particle system?

Like so:

Emit all 'particles' in the first frame
Set emit from faces
Grid
. let resolution match you subdivision
assign the group and pick whole group or let blender pick random group member


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Render of Planet Earth in Blender Render and Cycles
A couple of months ago I created this image with the help of this Blenderguru tutorial. The Blender Render engine is used. Although only one sun lamp is used you may note that the shadow side of the earth is not black.

Now I have a little understanding of cycles I tried to build the planet earth in cycles with this result. Note that the shadow part is very dark / black although I used a very tiny Ambient Occlusion

I really prefer the blender render result because
1) the blender render planet is a "true blue planet" with lots of water and blue tints. In the cycles render there seems to be much less water
2) the africa continent seems very large in the cycles image
3) the clouds are very present in the cycles image and make it a more greyish image.
It looks like that the proportions are different. Did I make some mistakes with the texturing. Or is this simply the kind of differences that are normal ? I thought that Cycles was the more photorealistic render engine, but is this true and are there better engines ? Were did I go wrong with my cycles render ?
After the answer of Gandalf I applied his volume shaders to my Atmosphere and I also added subsurf modifier to the atmosphere. This is the result. I used the same shader as Gandalf. I guess I should change the distance between the atmosphere and the earth ??

Nothing most likely. Cycles is more realistically based, and is a completely different engine. You should not expect the same results, as if that is the case, you should use the much faster internal engine instead.

Are you using UVs to map the texture?

no, I use Texture Coordinates (generated) in the Cycles render and in the blender render also generated coordinates are being used. By the way, I re-uploaded the blend file and now packed all the images

It is not only that I prefer the blender render result but also I think the dimensions of the image mapping in the cycles render seem out of proportion

for me the relevance of this question is A) did I do something wrong (landscapes and cloudscapes have very different dimensions) ? and B) why are these images so different ?

@cegaton Any ideas ?

Not having the two files to comprare I can only guess... if the size of the images used as textures is not the same, that means that the mapping coordinates of  both files are not the same. If you are looking for accurate mapping you need to unwrap your object and use UVs. The images are going to look very different in cycles or internal no  matter what. Both renderer engines deal with lights and textures in a radically different way.

You might also want to look at this question: http://blender.stackexchange.com/questions/10741/what-is-the-best-way-to-unwrap-a-sphere

Cycles is capable of utilizing physically-based rendering techniques, but that doesn't inherently make every render appear photo-realistic. See How is Cycles different from Blender Internal?
To get a nice atmospheric scattering effect in cycles, I'd suggest wrapping your earth sphere in a slightly-larger sphere with a volumetric material such as this:

Result:

Note that these values are arbitrarily hand-picked based on what I thought "looked nice". If you are after accuracy you'll probably want to do a bit more research than I did ;)
It could use some tweaking, but it does look somewhat similar to actual photographs of the earth:

Note that in the above setup the atmosphere is a constant density. The real atmosphere gets less dense higher up, creating a subtle falloff. This is pretty easy to simulate with a spherical gradient texture, but will vastly increase render time.

If you don't see the edge of the atmosphere very close up in your render, simulating this may not be necessary.

In response to the edits to the question:
To get rid of the grid-like pattern, add a subsurf modifier to the atmosphere sphere and increase the number of subdivisions until it's no longer apparent.
The reason the earths atmosphere appears bluer at the edges is because light which travels farther through the atmosphere is more likely to be scattered off air molecules. Since rays closer the edge of the atmosphere which travel farther through it, they appear bluer:

Keep in mind that thickness matters a lot with volume rendering, so another thing you can tweak (in addition to the density etc.) is the scale of the atmosphere object (adding more or less atmosphere on top of the ground)
Here's the .blend of my setup:

Textures intentionally omitted
Note that everything is just eyeballed; nothing is based on real-world data.

This conversation has been moved to chat.

If you prefer the blender internal render for this kind of scenes (as I do), then you can use inverse Fresnel material approach to simulate atmospheric effects including outer glow, color gradient, soft edge near the space etc. Here is:

The basic nodded material setup with source fresnel showed on the right
And final result you may expect from it

It does increase render time, but just a little bit.


text:
Having trouble with multiple animations triggered by key presses in the game engine
I have very little Python knowledge and I'm trying to get a character to play one animation when the A key is pressed, a different animation when the D key is pressed, a different animation when the W key is pressed, and finally a different animation when both the A and D keys are pressed at the same time. I hooked up the appropriate keyboard sensors and action actuators to a python controller and when I test the character, it works with the exception of one problem. Depending on how the keys are pressed in various combinations (not entirely sure which combinations are at fault) the animation will sometimes get stuck as if Blender doesn't recognize that a key has been released and it keeps on playing that keys animation or it will stop playing the animation but will be frozen on a particular frame. I've tried numerous variations of the code, to solve the problem but nothing works and I've tried using just logic bricks without any code, but nothing eliminates the problem from occurring with certain key combinations (like pressing A and W at the same time and then releasing the W key slightly before the A key. This causes the character to get stuck on the A key's animation)
Here is the code I used:
import bge

cont=bge.logic.getCurrentController()

a=cont.sensors['a']

d=cont.sensors['d']

left=cont.actuators['turn_left']

right=cont.actuators['turn_right']

stationary=cont.actuators['stationary']

w=cont.sensors['w']

walk=cont.actuators['walk']

if a.positive and d.status==0:

    cont.activate(left)

else:

    cont.deactivate(left)

if d.positive and a.status==0:

    cont.activate(right)

else:

    cont.deactivate(right)

if a.positive and d.positive:

    cont.activate(stationary)

else:

    cont.deactivate(stationary)

if w.positive:

    cont.activate(walk)

else:

    cont.deactivate(walk)

I've tried everything I can think of but its become a great frustration. Please help!
Here is a screenshot:

@Amir The preferred formatting for keyboard keys is to use  formatting. E.g. A.

The problem is that the action actuator is broken since 2.62. When you play different actions one after the other at the same object, some animations will not be shown. The bugtracker contains several reports already.
To avoid that problem you can play the animations with python via playAction().
It is not my preferred solution, but as long as the action actuator does not work as expected, it is a solution.

Game engine has died, I wouldn't hold my breath for getting this fixed.  https://developer.blender.org/rB159806140fd33e6ddab951c0f6f180cfbf927d38

This is an irrelevant comment. The bug is present since 2.62 (now we have 2.79). Do you really think I expect this will be fixed in future?


text:
Is there an alternative to point density for rendering with GPU?
Finally working with some clouds. Rendering is horribly slow with my i5 CPU, would be much better with a GTX 970, but if I try that then shaders that use point density no longer work. Is there a good alternative to point density that is renderable with a GPU in Cycles?

Not really. Point density is pretty unique. You could try to use a particle system on the object (just spawning on the surface, i.e. no actual physics) with various spheres or distorted shapes from displacement maybe, but I've never manages to get it looking quite the same. If you really need point density, I'd anyway recommend using Blender Internal's - yes it is CPU, but goes decently fast, and just requires compositing into your Cycles GPU render in post.

As of version 2.77, Point Density rendering is now supported on GPU. Additional color capabilities should appear in 2.78.

There is a current bug report (T47794, March 14, 2016) that reports occasional stretching artifacts in a Point Density texture when rendering on GPU.


text:
How can I make stubble facial hair in Cycles?
How do you add stubble facial hair in blender cycles to a character? I have tried using the particle system for hair but it just makes uneven patches of hair that is the skin color of my character.

By default particles will use the same material as the object they are emitted from. To use a custom material for your particles you need to add another material to your object -

then assign that material to your particles in the particles render settings.

Thanks, do you know how you would make the hair stubble? Like really short, I have tried to make it stubble but when it renders it is just big patches of hair. I have tried messing with particle settings and googling it but there seems to be nothing for making it stubble.

Try a small hair length around 0.02 This tutorial covers a short beard.


text:
How to make things stay on animated character
How do you make it so something like a pair of glasses stays on a rigged character model in cycles? Whenever I move my character I want the glasses to stay on them. I have tried parenting the object but it just makes it disappear and do a bunch of weird stuff like that.

You have to parent the glasses to the Head Bone. So then, when the animated character moves, the glasses move with the head.
So first, select the Glasses, then  Shift+RMBto select the armature. Then go into Pose mode of the armature and select only the head bone. After that, press Ctrl+P to parent the Object to Selected Bone


text:
One Render layer with a transparent background and one with sky?
How do you get one render layer to have a transparent background
and the other to have a sky?
I mean in the shading panel where it says "Alpha: Transparent (or) Sky"

I think you may have to use different scenes instead of render layers, like this method for rendering a pass with no DoF.

I am afraid that wont be possible, because I have to use the same camera  movements from the original scene in the exact same place.

You can link the same camera object to both scenes and it will follow the same animation and have all the same settings.

Keep the Sky option on.

Then make two render layers. One with The sky option enabled.

And one without it:

The one with the sky disabled will have a transparent background.


text:
My video file won't open
After reading this other question I tried to render a video from an animation. I added the images to the filmstrip and rendered the video. But the file cannot be opened (The operation couldn’t be completed. OSStatus error -50.)
When I open the images in Photoshop and render a MP4 movie everything works. What is my error?

You will have to delete the strips in the Video Sequence editor windows.
Rendering to windows will work after you removed them.
What happened?
Basically the creator of the blend file have already rendered out the sequence of frames on his computer. He has also imported them as sequence strips into the video sequence editor for editing and then planned to output them into a movie file. When you downloaded the file, those film strips are targeted to render out when you hit the render button. Since those sequence file are not pack within the blend file ... you would get transparent frames.

Note what cegaton said below in the comment would also work.

Or uncheck the sequencer on the post processing section see: http://blender.stackexchange.com/a/14801/1853


text:
What skills are required to model / sculpt this head?
I came across this image in a dutch newspaper and I would like to know how you would create this head in Blender ? What kind of skills do I have to learn ? What are the most important techniques to be used ? Or can it be done much better in another software package ?

I would use "Make Human" http://www.makehuman.org/ and import the resulting model into Blender. I've never used Make Human so I can't instruct you on how to do this. (I think it's relatively simple to use).

It should be possible to do in Blender. You should use basic modeling (blocking the shape of the head), sculpting (refining the head), lighting (to not ruin results of materials / compositing it's good idea to setup lighting in the beginning), materials, rendering and compositing (to enhance results of lighting and rendering).

Ok Guys, maybe this question is too broad, But have you seen the fabulous answer of Stacker ? I guess this is very valuable info for me and many others. And where should I post this question, if not here ?

As already mentioned in the comments, make human is the shortcut.
A  shape created by this awesome tool in two minutes, limited in details but could be tuned wihtin blender:

Another way to re-create this with modelling either trace the contours of a background image. Or use subdividing, insets and proportinal editing:

After ripping V the mouth, the mesh could be easily adjusted to whatever head shape you want. Kudos to What's the best way to model organic shapes?

You might also need this addon: http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Add_Mesh/Add_Gear

WOW !! this really helps :) you should have waited 15 min, then you could have the bounty premium ;)


text:
Why should I never ever use "Convert Premul" on Cycles renders?
On this question, When trying to overlay images using Alpha Over for green screen work , I used premultiply Alpha, it was the only option that would give me clean key without the background bleeding over. A comment states Never use that "Convert Premul" option on Cycles renders. Ever.
Why?

You misread the answer, and my suggestion wasn't terribly clear. Any imager should be "pro" associated (aka crap term "premultiplied") alpha.
There is a good reason, and I will expand this answer when I find some time later.
The bottom line is that only associated alpha models a real-world correlation, where unassociated doesn't.
Only associated alpha manages to model both occlusion and emission. Glows, convolutions,  motion blurs, and a plethora of other transparent / translucent effects can only be modeled with associated alpha.
Think of alpha as selecting the over operation. The Alpha over node actually assumes associated alpha and performs the correct over operation, which is FG+(1-FG.a)BG.RGB.
Unassociated alpha can do none of these things. This is at least one of the reasons that PNGs are never used in a post production pipeline as they are incapable of using associated alpha. From the EXR Technical Introduction:

Calling the color channels “premultiplied” does not mean that the
color values in an image have actually been multiplied by alpha at
some  point  during the creation of the image, or that pixels with
zero alpha and non-zero color channels are  illegal. Non-zero color
with zero alpha is legal; such a pixel represents an object that emits
light even though it is completely transparent, for example, a candle
flame or a lens flare.
In  the  visual  effects  industry  premultiplied  color  channels
are  the norm, and  application  software packages typically use
internal image representations that are also premultiplied.

http://www.openexr.com/TechnicalIntroduction.pdf
From the actual TIFF specification, regarding TIFFTAG_EXTRASAMPLES tag that denotes what type of samples are stored:

The difference between associated alpha and unassociated alpha is not just a matter of taste or a matter of maths.

Associated alpha is generally interpreted as true transparency information.

http://www.awaresystems.be/imaging/tiff/tifftags/extrasamples.html
Again, never, ever, use unassociated (crap term "straight" or "key") alpha, and instead associate it. This is what the unfortunately named "Convert Premul" does in the Alpha Over node. However, on direct Cycles renders, it is already associated and is never needed.
There is exactly one edge case that you must unassociate alpha before processing, and that is on colour corrections. To do so, you must be careful and skip on zero alpha. An alpha value of zero with nonzero RGB is entirely valid, and represents an emission without occlusion. Examples include reflections, glows, glares, flares, fires, etc.
The only time "Convert Premul" should ever be used is if the imager knows she is feeding it unassociated alpha, but like a good imager, she would never be using anything except the One True Alpha, associated alpha.
Further reading:
Zap Anderssen of Autodesk now:
http://forums.cgsociety.org/archive/index.php?t-278718.html
Larry Gritz of OpenImageIO and Sony Pictures imaging team:
http://oiio-dev.openimageio.narkive.com/aaTdld9U/handling-unassociated-alpha#post2
Jeremy Selan, two time Academy Award winning imager behind OpenColorIO, now at Valve:
https://groups.google.com/forum/m/#!topic/ocio-dev/ZehKhUFqhjc
The Infamous Adobe Photoshop thread. Pay key attention to the names, as there are many imaging legends in it, including Zap Anderssen dismantling one of the head developers of Photoshop, only to have Florian Kainz of ILM back up Zap's take on it:
http://forums.adobe.com/thread/369637
EXR Technical Introduction:
http://www.openexr.com/TechnicalIntroduction.pdf
I likely misspoke in the original question as, from memory, I can't remember exactly what that goofy keying node delivers in terms of alpha. I suspect it is unassociated, which makes the "Convert Premul" option work. Generally however, to avoid oopsies in the code etc., it is prudent to manually associate your alpha and control the merging to prevent data loss in the RGB channels. I still stand by the advice, however; always try to maintain a consistent state of alpha, and when you deviate, do so under scrutiny.
Additional information for implementation via nodes or software
There are three states for imagery with emission values encoded in the RGB channel, and an additional occlusion channel.

Associated. The RGB emissions are “as is” and represent the final emissions required. This may include zero alpha with nonzero RGB, such as the aforementioned case of reflections, fire, etc. To disassociate the emissions from the degree of occlusion, use a divide skip zero alpha. Leave any RGB emissions in the zero alpha case, as they could be glares, flares, fire, or reflections.
Unassociated. Here the alpha is not encoded. That is, the RGB represents the emissions without occlusion taken into account. To associate in the case of Unassociated alpha, use a simple multiply which will scale the RGB emissions by the linear degree of occlusion.
Disassociated. Here the alpha started life properly encoded as associated alpha, but has been disassociated to conduct colour transforms. To properly reassociate the data, multiply but skip zero alpha. That is, leave any emissions in the RGB channel as is.

I'm on the same page with troy_s regarding the use of misleading terms in programs UIs.
This kind of questions are the result of a poor choice of terms for the functions. In this case, "convert premul" is a misleading label. Even the term "premultiplied" is misleading, as the very EXR specification states in the last page: It doesn't necessarily mean the plate was multiplied by the alpha.

What would the process with the very small number be like? Alpha += 0.00...1 > Unassociate > (e.g.) Gamma correct > Associate > Alpha -= 0.00...1 ?

Disassociate / Unpremultiply is a divide skip zero. That is, if the alpha is zero, leave the RGB values as-is, and multiply the RGB in the case of nonzero by 1/alpha or divide by alpha.  To Associate / Premultiply, multiply not zero. That is, if the alpha is zero, skip and leave as-is, and multiply by alpha in the case of not. In a proper imaging pipeline, "gamma", or more usefully nonlinear transfer functions, should never be at play and you should only operate on linearized data, be it scene linear or display linear. Within Blender's compositor this is the case via transforms.

I believe it's that Cycles renders have straight alpha. Straight means that, even though the pixel is transparent, it still has pure, unaltered color information. Like R255 G35 B48 A10.
Converting straight alpha to premultiplied is essentially multiplying the color info with the alpha, so R255*(10/255) G35*(10/255) B48*(10/255) A10 becomes R25 G3 B5 A10.
If you tick 'Convert Premul' you're implying the Cycles render has already been premultiplied (which it hasn't) and Blender will try to readjust color values to accommodate that. The alpha rim gets wonky.
It's not that straight alpha is technically 'better' than premultiplied alpha. Premul alpha saves disk space so it's the preferred option for real-time 3D and like. It's just that the algorithms for combining straight and premul pictures are not compatible. My guess is that Blender prefers the straight variant, so you have the option to convert premul to straight if needed.

This is wrong. All raytracers model physical reality, and as such, unassociated alpha (aka "straight" or "key") can never be generated as it has no real-world counterpart. This is entirely incorrect, and alpha relationships are much more than a simple mathematical divide or multiplication.

Just as troy_s, this is incorrect. It's exactly the opposite. Cycles renders associated (premultiplied) alpha.
As it's already associated, the alpha over operation doesn't have to multiply the foreground * alpha again, so that's why you don't have to activate that checkbox for cycles renders.


text:
Layering of materials / shaders - how does it work?
Layering of materials is done for instance when building a shader for a mirror like here or a shader for car paint like here. But how do you build the "composite shader" ? Is this done by creating two node groups and making the node group of the lowest layer an input for the node group of the top layer or using an Add Shader ? How would you for instance create the mirror shader combining the glass shader and the Silver Coated Aluminium shader of this Post ? I hope this is not a dupe ...
Maybe my language is not very precise when talking about combining materials. In this PBS tutorial about building shaders CynicatPro "combines" two node groups to create a car paint shader.

Now, when having the shader for Glass and the shader for Silver Coated Aluminium I am not sure what to do ? I have read the article about when to add the shaders together and when to mix them: blender.stackexchange.com/questions/420/… but at the moment I don't understand how to produce the mirror shader .... Add/mix shaders ? Or "combine node groups" ?

You don't combine the glass shader and silver shader, they are different meshes on top of each other - different physical materials. In cycles you can only composite shaders by adding them or mixing them (also posible with a mask). Every shader is different - what you want to ask is when to add the shaders together and when to mix them: http://blender.stackexchange.com/questions/420/difference-between-add-shader-and-mix-shader

I hope I made my question more clear / specific ?

I see now what you mean with combining the node groups. They are called pass-through shaders but they are nothing more than visualization helper. If you would go inside them, there are ordinary mix/add shaders inside, nothing fancy. Mix or Add shaders takes 2 input shaders - this is just grouped with one of the inputs exposed so it is easier to work with.

@Jerryno Would you mind telling/explaining me if I have to add or mix your Mirror and Aluminium Shader ? I think Add ... because I think you want to add the qualities of the two materials and not mix them

What are you trying to create? Some sort of glass silver alloy? That does not exist. You do not want the surface to be both transparent-reflective (glass) and reflective (silver) but you want 2 surfaces with different properties on top of each other. See my first comment. Btw. you don't usually want to add shaders together but rather mix them as adding them does not preserve energy. See the link in my first comment.

I stumbled into your interesting answer on how to create the mirror shader and I think I do understand the part about the glass shader and the part about the aluminium shader but I am just wondering how to put them together to construct the mirror shader. That's all. I just want to understand how I can create the mirror shader.

Let us continue this discussion in chat.


text:
Keying node in compositor. How can I associate the alpha channel so that it works with the Alpha Over Node?
(As a follow-up to this question)
I'm trying to overlay a a green-screen plate over a 3D background.
I create the key with a Keying node and the overlay with an Alpha Over node.
I can get a clean key by enabling Convert to Premultiplied.

Whereas if I leave the Convert to Premultiplied off, the key does not work.

The reason for this, as explained on this anwser:

The Alpha over node actually assumes associated alpha and performs the correct over operation, which is FG+(1-FG.a)BG.RGB.
Unassociated alpha can do none of these things.
[...] it is prudent to manually associate your alpha and control the merging to prevent data loss in the RGB channels. I still stand by the advice, however; always try to maintain a consistent state of alpha, and when you deviate, do so under scrutiny.

So the question is: what is the correct way to associate the Alpha Channel crated by the keying node, so that it works with the Alpha over node without resorting to the convert to premultiply option?

green screen element can be downloaded from the mango project https://download.blender.org/mango/first-footage.zip

What's the file extension of the input image ?

@ Mr Zak its an EXR file

There are potentially a few issues with either "Convert Premul", converting alpha, or a simple multiply across the channels, that may not be entirely obvious at first. It is a point of confusion in that that no node should deliver unassociated alpha as the entire compositor assumes associated values. Sadly the node used here, does.
One issue, with particular attention to pulling a key, is that your edges will likely not be of the correct luminance value to blend seamlessly. That is, when a subject is shot against a green screen, the alpha channel that is produced would be a ratio of the foreground against the background, which in this case is some non-black value of the screen used. The resulting output ratio isn't going to be the same as an object set against non-emitting pixels. Those semi-transparents can be extremely tricky to get the ratios correct on without having a good grasp on the behind-the-scenes models.
The second issue would be with associating is that you can destroy RGB information. As per the OpenEXR Technical Introduction, alpha with a greater ratio RGB is entirely valid and represents emission with a lower degree of occlusion. The problem is that if you craft this in an RGB image, zero alpha will destroy this information on the multiply.

Calling the color channels “premultiplied” does not mean that the
  color values in an image have actually been multiplied by alpha at
  some point during the creation of the image, or that pixels with zero
  alpha and non-zero color channels are illegal. Non-zero color with
  zero alpha is legal; such a pixel represents an object that emits
  light even though it is completely transparent, for example, a candle
  flame or a lens flare.
In the visual effects industry premultiplied color channels are the
  norm, and application software packages typically use internal image
  representations that are also premultiplied.

To work around this, a carefully crafted RGB against zero emission RGB values can be associated manually.
Once you have a representation of your emission levels in RGB, which is effectively RGB values against black, you can use whatever technique you desire to assign the alpha channel. For example, if you have a blue glow with low or zero occlusion (alpha), you would want the equivalent occlusion values properly set into your base. "Set Alpha" will assign the alpha directly to the alpha channel, and the result should be correct[1].
TL;DR in your sample, "Convert Premul", using the alpha conversion node, or strictly a simple multiply will all work as expected, with a rather large caveat being the first issue above. You would ideally want your image to represent emission on the semi-occluded pixels, which as any keyer would tell you, is quite a dance of artistry. Using that canned After-Effects-Esque "Keying" nightmare node won't help either, as it assumes a single luminance / RGB value to compare against across the whole green screen, which is never the case, and will result in whack or rather cheated values, which will impact your final composite. An alternative that might get you closer is to inpaint and use a distance node on the RGB values, which will at least pull data from the fully non-occluded plate elements and push them into the semi-transparent regions. This will result in a luminance difference that is closer to what was behind the actual pixels in question.
[1] Note that there are largely two primary methods to do this. One is probabilistic, aka A+B-AB and the other is non-overlapping, which is A+B. If you are certain your geometry doesn't overlap for the pixel in question, the latter is correct. If your geometry overlaps, such as a transparent window atop of another transparent window, the former is correct.

"inpaint and use a distance node on the RGB values" can you please show an example of how to do this?

I realized I left this comment hanging. Basically you would want to have an image that approximates what is behind your semi-transparent regions. Inpaint can do a decent job of this. Once you have an inpainted version of your plate, you can feed that and the original to a distance node to calculate the distance between the RGB background and foreground. That distance ends up being your transparency ratio to combine with your fully opaque regions.

This has been fixed on blender version 2.92.
The output from the keying node now outputs associated alpha, as it should be.
As explained here: https://developer.blender.org/rBf68c3d557aa

Compositor: Ensure keying node result is pre-multiplied

Historically the result of the keying node was violating alpha
pre-multiplication rules in Blender: it was simply overriding
the alpha channel of input.

This change makes it so keying node mixes alpha into the input,
which solves the following issues:

The result is properly pre-multiplied, no need in separate alpha-convert node anymore.
Allows to more easily stack keying nodes. This usecase was never really investigated, but since previously alpha is always overwritten it was never possible to easily stack nodes. Now it is at something to be tried.
Unfortunately, this breaks compatibility with existing files, where
alpha-convert node is to be manually removed.

Use Add>Convertor>Alpha Convert set to Straight to Premul to easily and quickly multiply the R, G, and B components of the image by the alpha. This should give you an image with the associated alpha that alpha over expects.


text:
Unable to pick color option?
I am new to blender and trying to start off simple with minecraft animations. I am watching a video tutorial about how to change a character's "skin", it's easy if the options are enabled but it seems mine are not. I was wondering how do I enable these options?
This first image is what I see:

This second image is what I am trying to achieve but the options are not there:

I hope this is an easy fix, thank you in advance. I am using cycles render and the latest version of blender (downloaded blender yesterday).

You selected the wrong shader.

Click on Mix Shader and select Diffuse BSDF instead.

It made the guy entirely white besides his eyes and eyebrows, http://i.imgur.com/a6rp951.jpg - I figured it out, you need to change the color option to "image texture" and go from there in terms of setting the skin. Thank you very much Photon! :D

You're welcome. Have fun with Blender :)