Custom drawing/rasterization with a `CompositorEffect`

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Godot Version

4.3

Question

How to implement a CompositorEffect with a draw list, not a compute list?

Details

I am learning to use the Compositor and I’ve already got compute shaders working with it. But now I want to try implementing custom drawing (rasterization of vector shapes and text) as a CompositorEffect. So that I can plug it into the Compositor, and apply some other CompositorEffect on top (e.g. change brightness).

Should I use RenderingDevice’s draw_list and render_pipeline in the _render_callback() to achieve my goal? If yes, then how to do that? I’ve found the example in the docs describing a “simple drawing operation”. But what is it drawing, just transparent colors? Where to does it draw these colors? It says that draw_list_begin() “Starts a list of raster drawing commands created with the draw_* methods.” I’ve found how to use draw_*() in custom drawing, but how to connect these functions to draw_list? Where to place them? Also, how to initialize the render pipeline, or raster_pipeline in the case of the docs code snippet. render_pipeline_create() has 11 arguments; and I don’t understand how to properly assign most of them. The unclearest ones for now:

  • vertex_format – vertex_format_create() requires an array of RDVertexAttribute which lack documentation,
  • primitive – say, how to draw an arc or text if there are no similar entries in the RenderPrimitive?
  • shader – what kind of shader does it want?

So, I’ve got plenty of questions, and I don’t even know where to start reading up. I haven’t found comprehensive tutorials about render_pipelines and draw_lists but maybe you’ve found/prepared/recorded some? Maybe there are some clear demos using these? Or maybe you’ve got some general ideas on implementing a drawing CompositorEffect? Any advice/suggestion/lead is appreciated!