Particle Instances not excluded in alpha channel mask
Closed, ArchivedPublic

Description

I have a pieces of a rendering I am working on. This is the gravel with all the landscape particle instances. If you look at the generated alpha channel mask, you will see that none of the small plants and bushes are excluded in the mask, like the trees are. The tress are group instances. If I render this same mask using B-Maxwell, Maxwell Render for Blender, all of the particle instances are included in the mask. I do this because the client might say make the gravel lighter or darker. This can then be done easily in the compositor or Photoshop. If the plants are not excluded in the alpha, they will get changed as well. Not good. I hope this is a bug and can be fixed.

dual E5 2660 v3's (2.6 ghz) (40 Threads) Z10PE D8 WS, 96 gigs of ram win 7 x64 GTX 970
Windows 7, Blender 2.79 official Build

Details

Type
Bug
Bastien Montagne (mont29) triaged this task as Incomplete priority.Nov 3 2017, 3:44 PM

Please follow our submission template and guidelines, also read these tips about bug reports, and make a complete, valid bug report, with required info, precise description of the issue, precise steps to reproduce it, small and simple .blend and/or other files to do so if needed, etc.

System Information
dual E5 2660 v3's (2.6 ghz) (40 Threads) Z10PE D8 WS, 96 gigs of ram win 7 x64 GTX 970 Windows 7,

Blender Version
2.79 5bd8ac9

Short description of error
This is a gravel base mesh with a plant particle instance mesh. If you look at the generated alpha channel mask, you will see that none of the small plants are included, like the cube, in the mask. If I render this same mask using B-Maxwell, Maxwell Render for Blender, all of the particle instances are included in the mask. I do this because the client might say make the gravel lighter or darker. This can then be done easily in the compositor or Photoshop. If the plants are not included in the alpha, they will get changed as well. Not good. I hope this is a bug and can be fixed. And I should be able to achieve this without converting the particle system.

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps

Add particle mesh objects to plane render RGBA the particle objects are not included in alpha mask.

See attached blend file.

Vuk Gardašević (lijenstina) raised the priority of this task from Incomplete to Needs Triage.Nov 11 2017, 1:49 PM

Additional information was provided.
Setting to Needs Triage.

Brecht Van Lommel (brecht) claimed this task.

B-Maxwell might have a different interpretation of that setting than how it originally worked in Blender, so this is not strictly a bug.

I think the Blender interpretation makes sense, if you put an object in a mask layer, then all objects that it instantiates will be masked out as well. If you for example have two characters from a linked dupli group in different layers, then you still want to be able to mask out both characters individually, even if they might share some objects on the same layer in the original .blend files. As far as I know this is quite consistent with how other software works.

For this .blend file, you can create separate objects for the ground and the particle instancing, and put those in different layers.