error with glsl input: error 30015: undefined identifier 'gl_VertexID'

[TomSirgedas]

Hello! I'm interested in automating the translation of GLSL shaders to WGSL. But, I'm running into a problem when the vertex shader uses gl_VertexID. Any ideas?

vertex.glsl

#version 300 es

out vec2 _TexCoord;
uniform vec2 _TexCoords[4];
uniform vec4 _Positions[4];
void main( void ) {
   gl_Position = _Positions[gl_VertexID];
   _TexCoord = _TexCoords[gl_VertexID];
} 

Command line and output:

C:\Tmp\slang>c:\Proj\SLANG\bin\slangc vertex.glsl -target wgsl -o out.wgsl -entry main -stage vertex -allow-glsl
vertex.glsl(7): error 30015: undefined identifier 'gl_VertexID'.
   gl_Position = _Positions[gl_VertexID];
                            ^~~~~~~~~~~
vertex.glsl(8): error 30015: undefined identifier 'gl_VertexID'.
   _TexCoord = _TexCoords[gl_VertexID];
                          ^~~~~~~~~~~

[juliusikkala]

You may be able to use gl_VertexIndex instead. This difference is due to Slang's GLSL compatibility mostly matching Vulkan-flavored GLSL, not OpenGL. gl_InstanceID and gl_VertexID are gl_InstanceIndex and gl_VertexIndex in Vulkan-targeting GLSL.

[TomSirgedas]

That does work, thank you!

[jkwak-work]

I will update the GLSL document later.
For now, I am keeping a note here

• [Tutorial] the first draft of on-ramp tutorial (for GLSL users) #5448 (comment)