add IS_VERTEX and IS_FRAGMENT to shader defines

[pailhead]

Allows for adding stuff to commons chunk for example.

#10750

[mrdoob]

If I remember correctly, you're not supposed to add anything before the precision line.

[pailhead]

You are right, I messed something up and added this thing twice. Still good to have per that other discussion?

[mrdoob]

Hmm, I cannot think of any specific use case for this right now, but I suspect it is indeed something handy to have.

[WestLangley]

Hmm, I cannot think of any specific use case for this right now, but I suspect it is indeed something handy to have.

It can't be handy if a use-case cannot be identified. :)

What is the compelling use-case?

[pailhead]

Cant link to the comment in the review in the other thread. Mrdoob suggested some glsl should be in the commons chunk but it exists in both very and frag. Say you want to add attribute float u_should_exist_in_all_shaders you can't use commons.

[pailhead]

Just to make this idea seem less idiotic, it is now becoming more obvious what was the use case for this.

common.glsl seemed like the most appropriate place to append code that should be in global scope. It is guaranteed to be in every shader, we would have access to the functions. The reason why it doesn't work is because the same chunk ends up in both vert and frag shaders.

Basically it was supposed to do what % global_vertex % and % global_fragment % should do in:

#11475

[pailhead]

Using the onBeforeCompile, i think i would really like this feature.

[mrdoob]

Could you elaborate?

[pailhead]

const myGLSL = 'attribute vec3 aMyAttribute;\n`

myMaterial.onBeforeCompile( shader=>{
  shader.vertexShader = myGLSL + shader.vertexShader // messes up extensions and such?
  
  shader.vertexShader = shader.vertexShader.replace( '#include <what>`, "?" + myGLSL  )
})

Actually now having written it like this it's not so much of a problem. I was thinking of something like

float sharedFunction( float i ) {}

#ifdef IS_VERTEX
attribute vec3 aMyAttr;
#endif

const myGlobalReplaceChunk = THREE.ShaderChunk.global + myGLSL

It could be like the first super mini step towards the properly named hooks etc. but maybe not worth it. Looking for void main and just appending above it might be good enough, not sure what would be the best pattern.