Think I’ve found the solution.
I looked through the FViewUniformShaderParameters available and did the opposite of WorldToClip which is clipToTranslatedWorld.
So now I have the sphere aligned to viewport in an orthographic way. It’s streyched to match the viewport whicg I expected. Also moving the sphere in X and Y in the world transforms it vertically and horizontally in the viewport which is what I want. These are going to be parented to the camera so I’ll need to add in extra offsets once they get in NDC space and to account for the aspect ratio.
The reasons for all this is to investigate a new way of doing fog of war without having to do the whole sceneCapture2D stuff. I am going to render spheres that are parented to the camera and render them to custom depth. I’ll also push them far into the distance using camera vector so that they render behind everything else. I can then use post processing to create the fog of war.
The post processing stuff works as thats just a world XY UV lookup.
I’ll start another thread once I’ve figured it all out.