Shader chunks: Overriding "texture2DBias()"

Astra · February 16, 2024, 11:56am

Hei,

Currently doing a lot of shader chunk editing, and I had this idea:
“What if I were able to override the texture2DBias() function?”

It’s used in basically all the different shader chunks to sample the different texture maps. Its also clearly a custom function since its not part of standard glsl. So being able to re-write this would allow for a consistent change to how all the texture maps of the materials are read. Meaning lots less work if say, you wanna do some funky changes to the texture tiling or something similar.

So I had a look through the PlayCanvas engine code and sure enough it looks like it’s defined in these three scripts:

github.com

playcanvas/engine/blob/52661f451883ad15876645b6a6219d9d68a0b4cc/src/platform/graphics/shader-chunks/frag/gles2.js#L33


      
          #endif
          
          #if COLOR_ATTACHMENT_6
          #define pcFragColor6 gl_FragData[6]
          #endif
          
          #if COLOR_ATTACHMENT_7
          #define pcFragColor7 gl_FragData[7]
          #endif
          
          #define texture2DBias texture2D
          #define itexture2D texture2D
          #define utexture2D texture2D
          
          // pass / accept shadow map or texture as a function parameter, on webgl this is simply passed as is
          // but this is needed for WebGPU
          #define SHADOWMAP_PASS(name) name
          #define SHADOWMAP_ACCEPT(name) sampler2D name
          #define TEXTURE_PASS(name) name
          #define TEXTURE_ACCEPT(name) sampler2D name

github.com

playcanvas/engine/blob/52661f451883ad15876645b6a6219d9d68a0b4cc/src/platform/graphics/shader-chunks/frag/gles3.js#L65


      
          #define pcFragColor2 pc_fragColor2
          #define pcFragColor3 pc_fragColor3
          #define pcFragColor4 pc_fragColor4
          #define pcFragColor5 pc_fragColor5
          #define pcFragColor6 pc_fragColor6
          #define pcFragColor7 pc_fragColor7
          
          #define varying in
          
          #define texture2D texture
          #define texture2DBias texture
          #define textureCube texture
          #define texture2DProj textureProj
          #define texture2DLodEXT textureLod
          #define texture2DProjLodEXT textureProjLod
          #define textureCubeLodEXT textureLod
          #define texture2DGradEXT textureGrad
          #define texture2DProjGradEXT textureProjGrad
          #define textureCubeGradEXT textureGrad
          #define utexture2D texture
          #define itexture2D texture

github.com

playcanvas/engine/blob/52661f451883ad15876645b6a6219d9d68a0b4cc/src/platform/graphics/shader-chunks/frag/webgpu.js#L52


      
          #define pcFragColor0 pc_fragColor
          #define pcFragColor1 pc_fragColor1
          #define pcFragColor2 pc_fragColor2
          #define pcFragColor3 pc_fragColor3
          #define pcFragColor4 pc_fragColor4
          #define pcFragColor5 pc_fragColor5
          #define pcFragColor6 pc_fragColor6
          #define pcFragColor7 pc_fragColor7
          
          #define texture2D(res, uv) texture(sampler2D(res, res ## _sampler), uv)
          #define texture2DBias(res, uv, bias) texture(sampler2D(res, res ## _sampler), uv, bias)
          #define texture2DLodEXT(res, uv, lod) textureLod(sampler2D(res, res ## _sampler), uv, lod)
          #define textureCube(res, uv) texture(samplerCube(res, res ## _sampler), uv)
          #define textureCubeLodEXT(res, uv, lod) textureLod(samplerCube(res, res ## _sampler), uv, lod)
          #define textureShadow(res, uv) textureLod(sampler2DShadow(res, res ## _sampler), uv, 0.0)
          #define itexture2D(res, uv) texture(isampler2D(res, res ## _sampler), uv)
          #define utexture2D(res, uv) texture(usampler2D(res, res ## _sampler), uv)
          
          // TODO: implement other texture sampling macros
          // #define texture2DProj textureProj
          // #define texture2DProjLodEXT textureProjLod

I tried treating these as shader chunks overriding material.chunks.gles2PS, material.chunks.gles3PS and material.chunks.webgpuPS. The compiler does not complain about these not being shader chunks, but neither does it seem to actually react to any changes I make to them.

Anyone got any ideas?

LeXXik · February 16, 2024, 12:22pm

Yeah, you can’t treat them as chunks. The engine imports them directly, so not sure there is an easy way to override. Maybe @mvaligursky has an idea.

mvaligursky · February 19, 2024, 11:36am

Nothing comes to my mind, other than a custom engine build. These are not chunks, but a platform (WebGL1, 2, WebGPU) compatibility macros and similar to allow us to compile a single shader to all those platforms.

Astra · February 19, 2024, 1:02pm

Ic… that makes sense.

Thank’s anyways