ShaderToRGB Node plugged to alpha does not work with Alpha Clip or Alpha Hashed mode in 2.90 #80919

New Issue

takaaki takeda · 2020-09-18T09:03:36+02:00

takaaki takeda commented

2020-09-18 09:03:36 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.86

Blender Version
Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: 0330d1af29
Worked: 2.83

Short description of error
If ShaderToRGB Node is plugged to alpha socket of another princepled BSDF, it does not work if blend mode is alpha clip or alpha hashed in blender 2.90.
This combination worked in 2.83

I attached a snapshot image in both cases 2.90 and 2.83.

Left image is 2.90, and Right image is 2.83.4.
The object becomes fully transparent in 2.90 case.
(Though, It works if blend mode is alpha blend.
The problem is only in alpha clip or alpha hashed mode.)

Exact steps for others to reproduce the error

Open the attached file in blender 2.83 and 2.90
Compare the viewport of both
ShaderToRGB_Problem.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.86 **Blender Version** Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: `0330d1af29` Worked: 2.83 **Short description of error** If ShaderToRGB Node is plugged to alpha socket of another princepled BSDF, it does not work if blend mode is alpha clip or alpha hashed in blender 2.90. This combination worked in 2.83 I attached a snapshot image in both cases 2.90 and 2.83. ![ShaderToRGB_AlphaClip.png](https://archive.blender.org/developer/F8894689/ShaderToRGB_AlphaClip.png) Left image is 2.90, and Right image is 2.83.4. The object becomes fully transparent in 2.90 case. (Though, It works if blend mode is alpha blend. The problem is only in alpha clip or alpha hashed mode.) **Exact steps for others to reproduce the error** - Open the attached file in blender 2.83 and 2.90 - Compare the viewport of both [ShaderToRGB_Problem.blend](https://archive.blender.org/developer/F8906878/ShaderToRGB_Problem.blend)

takaaki takeda commented

2020-09-18 09:03:36 +02:00

Added subscriber: @popqjp

takaaki takeda changed title from ~~ShaderToRGB Node plugged to~~ to ShaderToRGB Node plugged to alpha does not work with Alpha Clip or Alpha Hashed mode in 2.90

2020-09-18 09:18:18 +02:00

Germano Cavalcante commented

2020-09-21 19:27:08 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-09-21 19:27:08 +02:00

Can you provide a simple .blend file showing the problem?

takaaki takeda commented

2020-09-21 19:42:44 +02:00

I atached a blend file (ShaderToRGB_Problem.blend) here.

ShaderToRGB_Problem.blend

This file was saved by blender 2.83. (I checked that it can be read by 2.90 and the problem occurs there with my PC.)
When viewport render is turned to "Rendered", the suzanne becomes fully transparent in 2.90, while it is shown in 2.83.

I atached a blend file (ShaderToRGB_Problem.blend) here. [ShaderToRGB_Problem.blend](https://archive.blender.org/developer/F8906878/ShaderToRGB_Problem.blend) This file was saved by blender 2.83. (I checked that it can be read by 2.90 and the problem occurs there with my PC.) When viewport render is turned to "Rendered", the suzanne becomes fully transparent in 2.90, while it is shown in 2.83.

Germano Cavalcante commented

2020-09-21 20:02:25 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Jeroen Bakker commented

2020-09-25 15:48:17 +02:00

Added subscriber: @Jeroen-Bakker

Jeroen Bakker commented

2020-09-25 15:48:17 +02:00

During depth prepass the BSDF evaluation is skipped as at this point not all material resources are available. [See closure_lit_lib.glsl].

#if defined(DEPTH_SHADER) || defined(WORLD_BACKGROUND)
  /* This makes shader resources become unused and avoid issues with samplers. (see T59747) */
  return;
#else

This will output black color, what is converted and put in the alpha socket. An alpha of 0 is not visible, making the depth shader always discard the pixel.
As a work-around you could use the alpha blend mode, what does not rely on the depth shader.

There isn't a good solution for this as the depth shader must run first before anything as other effects (AO, shadowing) rely on the depth buffers. Surface shading happens later in the pipeline as they rely on AO and shadowing. For now I set it to known issue and add this as a limitation in the manual.

During depth prepass the BSDF evaluation is skipped as at this point not all material resources are available. [See `closure_lit_lib.glsl`]. ``` #if defined(DEPTH_SHADER) || defined(WORLD_BACKGROUND) /* This makes shader resources become unused and avoid issues with samplers. (see T59747) */ return; #else ``` This will output black color, what is converted and put in the alpha socket. An alpha of 0 is not visible, making the depth shader always discard the pixel. As a work-around you could use the alpha blend mode, what does not rely on the depth shader. There isn't a good solution for this as the depth shader must run first before anything as other effects (AO, shadowing) rely on the depth buffers. Surface shading happens later in the pipeline as they rely on AO and shadowing. For now I set it to known issue and add this as a limitation in the manual.

Philipp Oeser removed the

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ShaderToRGB Node plugged to alpha does not work with Alpha Clip or Alpha Hashed mode in 2.90 #80919