Baking: Geometry behind transparent materials is ignored #119610

New Issue

SleepyEngi · 2024-03-18T03:52:58+01:00

SleepyEngi commented

2024-03-18 03:52:58 +01:00

System Information
Operating system: Windows 10
Graphics card: rtx 2060 super

Blender Version
Broken: 3.0, 4.0 , 4.1+
Worked: 3.0 beta 22ffd69a91

Short description of error
This is a very specific behavior that I believe was misinterpreted as an error & incorrectly reverted

#93082

This disables the ability to bake geometry behind other geometry with transparent materials. When you bake an object with transparent materials, any ray that hits a transparent object just ends there, instead of continuing, resulting in the inability to bake objects that have several layers of transparency, such as hair cards or any material with opacity/transparency.

If you do not want those objects to show, they should be turned off in render. Or use a holdout material instead.
Looking at the fix, it seems to replace transparency with holdout, so that's the problem, I think. User should manually use holdout instead, this just disables the ability to bake multiple layers of anything with transparency, which is a big problem

Exact steps for others to reproduce the error

Open the blend file from the first bug report and try to bake a combined pass
Once the texture is done baking, transparency/opacity materials will not show anything underneath

The mentioned bug report's behavior is actually what you would expect from baking transparent materials, being able to bake multiple layers of alpha. I think this fix should then be reverted.

**System Information** Operating system: Windows 10 Graphics card: rtx 2060 super **Blender Version** Broken: 3.0, 4.0 , 4.1+ Worked: [3.0 beta 22ffd69a91](https://projects.blender.org/blender/blender/commit/22ffd69a91c9) **Short description of error** This is a very specific behavior that I believe was misinterpreted as an error & incorrectly reverted https://projects.blender.org/blender/blender/issues/93082 This disables the ability to bake geometry behind other geometry with transparent materials. When you bake an object with transparent materials, any ray that hits a transparent object just ends there, instead of continuing, resulting in the inability to bake objects that have several layers of transparency, such as hair cards or any material with opacity/transparency. If you do not want those objects to show, they should be turned off in render. Or use a holdout material instead. Looking at the fix, it seems to replace transparency with holdout, so that's the problem, I think. User should manually use holdout instead, this just disables the ability to bake multiple layers of anything with transparency, which is a big problem **Exact steps for others to reproduce the error** 1. Open the blend file from the first bug report and try to bake a combined pass 2. Once the texture is done baking, transparency/opacity materials will not show anything underneath The mentioned bug report's behavior is actually what you would expect from baking transparent materials, being able to bake multiple layers of alpha. I think this fix should then be reverted.

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SleepyEngi added the

labels 2024-03-18 03:52:59 +01:00

Pratik Borhade commented

2024-03-18 04:39:40 +01:00

This is a very specific behavior that I believe was misinterpreted as an error & incorrectly reverted
#93082

@brecht ^
Though baking is consistent in older versions as well. Not sure if this would be consider as a bug or request.

> This is a very specific behavior that I believe was misinterpreted as an error & incorrectly reverted #93082 @brecht ^ Though baking is consistent in older versions as well. Not sure if this would be consider as a bug or request.

Pratik Borhade added

Module

Render & Cycles

Status

Needs Info from Developers

and removed

Status

Needs Triage

labels 2024-03-18 04:39:59 +01:00

SleepyEngi commented

2024-03-18 07:05:17 +01:00

The way I see it, it was an incorrect behavior that was fixed but immediately reverted afterwards.

While searching about this issue, I saw lots of people asking for this but saying this may be a limitation in the software, but now I'm seeing that it's possible, just disabled by this change.

I've looked at the fix f0be276514
It seems to replace the transparency with a holdout material from what I understand. So the baking now behaves like it's a holdout instead of transparency. I think this is what's incorrect; the user would expect it to behave like transparency, allowing bake to draw geometry under transparent materials. To replicate the current behavior, they would use a holdout material instead.

For people who may be having this issue as well and looked this up: Here's how you can enable alpha baking. You will have to re-compile blender from the source code so here's a guide for that:

https://developer.blender.org/docs/handbook/building_blender/windows/

Go to this file:

intern/cycles/scene/integrator.cpp

Go to around line 246, and delete the following lines:

if (scene->bake_manager->get_baking()) {
/* Baking does not need to trace through transparency, we only want to bake
* the object itself. */
kintegrator->filter_closures |= FILTER_CLOSURE_TRANSPARENT;
}

Save, commit the change, and re-compile blender.

Results in the bake no longer ignoring alpha, and allowing you to properly bake multiple layers of alpha cards. See image for the now properly working behavior.

The way I see it, it was an incorrect behavior that was fixed but immediately reverted afterwards. While searching about this issue, I saw lots of people asking for this but saying this may be a limitation in the software, but now I'm seeing that it's possible, just disabled by this change. I've looked at the fix https://projects.blender.org/blender/blender/commit/f0be276514f2b7cae27c744ac80f999fbc69f12f It seems to replace the transparency with a holdout material from what I understand. So the baking now behaves like it's a holdout instead of transparency. I think this is what's incorrect; the user would expect it to behave like transparency, allowing bake to draw geometry under transparent materials. To replicate the current behavior, they would use a holdout material instead. For people who may be having this issue as well and looked this up: Here's how you can enable alpha baking. You will have to re-compile blender from the source code so here's a guide for that: https://developer.blender.org/docs/handbook/building_blender/windows/ Go to this file: `intern/cycles/scene/integrator.cpp` Go to around line 246, and delete the following lines: if (scene->bake_manager->get_baking()) { /* Baking does not need to trace through transparency, we only want to bake * the object itself. */ kintegrator->filter_closures |= FILTER_CLOSURE_TRANSPARENT; } Save, commit the change, and re-compile blender. Results in the bake no longer ignoring alpha, and allowing you to properly bake multiple layers of alpha cards. See image for the now properly working behavior.

Capture.PNG

606 KiB

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Baking: Geometry behind transparent materials is ignored #119610