I have a material in which I have to calculate the contribution of every pixel neighbors. Is there a better way of doing so than duplicating my code as many time as there are pixel neighbors?
The only way to do loops in materials is with a Custom Shader Expression:
Due to how shader code is compiled to be compliant with the various different platforms, loops can’t be implemented like they are in blueprints.
Hum interesting… is there a way to call a material function that I made in a custom shader expression or do I have to rewrite my function in the shader?
As far as I can tell, you’ll have to rewrite your material function inside the custom expression.
Aww too bad. Thanks anyway! Didn’t know about Custom Shaders 
This might help, but could also confuse. Once, I asked this same question about shaders.
I look at UE4 materials as being like shaders (not the same tho). The code used in shaders (GLSL, HLSL) is really the body of a for-loop, which determines how each pixel affected by that shader is drawn.
Adding a loop to a material (or shader) would be really inefficient.
Others with more shader experience might have a different view.
The thread looks interesting, I’m gonna read it later today. Alos I understand your thinking, since I used HLSL in the past, when working with materials, I think of them as HLSL codes. Thanks!