three-instanced-uniforms-mesh: add an ability to make varying non-interpolated (flat)

[upisfree]

I added an ability to make a varying non-interpolated, "flat".

Usage:

mesh.setUniformAt(uniformName, index, value, isFlat);

In my case I needed it to add 16 textures to the shader and have an ability to set the texture index.

[lojjic]

Nice addition! I wasn't aware of the flat varying glsl feature. 👍

Would you kindly add this to the documentation in the package's README.md?

[upisfree]

Yes, I will add this to README 👌🏻

I thought, maybe it's better to pass options object instead of one variable in case we will add more options in future?
Something like this:

mesh.setUniformAt(uniformName, index, value, { isFlat: true });

[lojjic]

An options object is a good idea. 👍

I'm also wondering... should we make flat the default? That does seem like it's probably the usually expected behavior given that we're trying to mimic uniforms which wouldn't be interpolated. In that case we could still add an option {interpolate: true} just in case somebody was relying on that undocumented behavior.

[lojjic]

Thinking about this more... Can you give a concrete example of where interpolation would be occurring that is messing you up? It seems to me like all vertices within an instanced draw would be receiving the same attribute value, so any interpolation would be between the same number...? How would two vertices of a triangle receive different values?