Might be handy if phong could have expressions implemented for multi-texturing, where rather than just working on color (which is implemented early in the shader), I could utilise various stages of the shader.
For example:
t0 could be like an incoming ior value I might like to use that relies on the specularity. Give me an option what shader variable I can override, in this case, finalSpecular, and let me drop in a textDat with my expression embedded, that would also allow me to access other calculations (say diffuseSum, outcol.rgb etc).
In a sense, the current expression allows me to access things like vVert.norm as they are defined and calculated before the colorMapColor is called. So it could be implemented in a similar way.
The advantage of this would be the ability to ‘slot in’ an existing chunk of pixel Shader code directly in the phongMat, without having to re-export when I want to turn another feature on / off.
Theoretically, this would allow non glsl savvy users (say a designer in the team) slot in useful tools in the familiar phong layout.