I am experimenting with some alternative rendering techniques, where the scene is represented as a mixture of parametrised SDFs and the final shading is done evaluating and mixing the SDFs for each fragment. The basic algorithm divides the screen into tiles, collects and sorts the SDFs intersecting each tile, and then invokes the final compute shader. There can be multiple SDFs affecting each pixel as they are partially transparent.
It seems to me that Apple's TBDR tile shading pipeline would be an ideal for for this type of algorithm, but I am not quite sure how to utilise it efficiently. Essentially, I was thinking about rendering bounding rects over the SDFs and leveraging the binning hardware to arrange them into tiles for me. What I need the rasterisation pipeline to spit out is simply the list of primitives per tile. But there is no "per-primitive-per-tile" shader stage, so this has to be done in the fragment shader. I could of course record the primitive ID per pixel, but this is complicated by the fact that I can have multiple primitives affecting each pixel. Plus, there will be a lot of duplicates, as there are usually not more than 5-6 primitives per tile, and sorting the duplicates out seems like a waste.
What would be the most efficient way to handle this? Is there a way to utilize the tile shading pipeline to simply build out a list of primitive IDs in the tile?
I was not able to find how to do what I wanted exactly (building a per-tile list of primitives), but a reasonable alternative is to build a per-fragment list of primitives using raster order groups. Works very well for my purpose. The approach, in case anyone is interested, is described in detail here: