I've done this for a project where the SDF functions are basically instructions, and you can build up instrictions on the CPU to send to the shader. and then the fragment shader runs them like a mini bytecode interpreter. You can tile up the screen to avoid having too many instructions per fragment. Kinda wild idea and performance may vary depend on what you're doing
The CPU builds an RPN expression (like "circle, square, union, triangle, subtract"), and the shader evaluates that in a loop.
I wasn't able to find examples of other people doing similar, but it seemed too useful to not be invented yet (:
Do you have any links to your work?
I'm writing some blog posts for my approach, but haven't finished them yet.
> You can tile up the screen to avoid having too many instructions per fragment.
I don't quite understand this part... If a given SDF needs N instructions to be evaluated, then how does tiling reduce N?
> performance may vary depend on what you're doing
Yeah, fill rate was not good enough with a straightforward approach, so I had to cache the evaluated distance values to a (float) texture atlas, then use those to render to screen. Luckily, standard bilinear filtering on distance values produces pretty decent results.
Yes sounds like the same thing! I also couldn't find anyone else doing it. Sounds super interesting what you're doing so I'd love to read your blog post when it's done if you want to drop me a message/email.
My project was using 2D SDFs for UI which meant you could use a bunch of primitive shapes and union/difference between them, and also add outlines, shadows, glows etc. This means that if you tile up the screen and use a union between two rectangles, only the tile with the overlap needs to calculate the union. It's a little more complicated in 3D with frustum culling.
I was doing it in webgl which doesn't have storage buffers and so I had to use uniforms to pass the data which is a huge limitation. Apparently webgpu could be better so I will try to figure that out one day. But it is early prototype so no links or anything yet.
