Fragment shaders (which this is) are quite resolution dependent: they are programs which execute at each pixel, so the input size to the algorithm contained in the shader is essentially equal to the resolution (it's not strictly, since other data can be passed in which the program iterates over—but it is fairly uncommon for shaders to make heavy use of loops or recursion from what I've seen).
I understand that, I'm quite acquainted with 3D programming and shaders. But I was under the impression that they were dependent on the resolution of the renderview, not the device.
