I have received a lot of questions about making the tutorial work on 5.3.
Actually, it is pretty simple and will work out of the box, except one change.
In 5.3, ability to sample render target from Render Target 2D data interface was removed, in favor of sampling render targets through Texture Sample Data Interface.
For that, Roughness Integrator Simulation stage and its script needs to be changed as follows:
Also, you will need to edit material function MF_GrabPixelAttributes, and change sampler type of pixel attribute render targets to Linear Color, and open each render target asset in content browser and re-save it. Without it, preview material will fail to compile:
