Question

I have noticed that texture have a field names “value” in all the shaders but it seems that this fields is never used.

Example :

tDiffuse: { type: "t", value: 0, texture: null },

What is the purpose of this field ?

Thanks

Answer 1

It is used.

It defines in which slot a texture needs to be stored. A slot is a place where a shaderprogram can access the texture trough samplers. This is indeed mostly 0 becuase we use only 1 texture in a shader. But if we wanted multiple textures being accessed in the shader the then the value needs to be changed to the number of slots nessecary.

Like you can see here:

https://github.com/gero3/three.js/blob/master/src/renderers/WebGLShaders.js#L1392-1397

map is the first texture. (slot 0)
envMap is the second texture. (slot 1)
lightMap is the third texture. (slot 2)

For every texture you use in the shaderprogram , you must choose a new slot.