What is the concrete uses of GLSL / HLSL ?

[Deathrey (DeathreyCG)]

@zubetto

Thanks for the answer, I think the “collapse” term is misleading. In other words, I would like to know if the instructions of a custom node will be executed for each pixel or only once if all of the inputs of this custom node are constant for the whole draw call. As far as I know there are pixel and vertex shaders and the output of a vertex shader is the input for a pixel shader. In my understanding, UE material editor do the work for us, deciding which part of a material nodes forms the vertex shader and which part forms the pixel shader. If all of the inputs of an expression formed by a group of material nodes are constant for the whole draw call, then UE places corresponding instructions in the vertex shader (or somewhere else) rather than in the pixel shader. That’s how I understand what the constant folding is. So, what happens if I change the Sin function in the documentation example by a custom node that only accepts Time as input. Will corresponding instructions be placed into the vertex or pixel shader? How the pixel and vertex shaders are designated in HLSL?

Unreal’s constant folding mean that material networks are evaluated, and any inputs on any pins, that are evaluated as constants, are collapsed to such. This is the only part of optimization you are missing out when using custom node.

There is no kind of decision about vertex/fragment shader you are mentioning. If a node is used in pixel shader related material inputs, it will be part of pixel shader. If it is part of vertex shader material inputs(world position offset, custom UVs, vertex interpolator), it will be part of vertex shader.