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Trying to put a structure in place that we can actually optimize.
Initially just implementing a passthrough mode, this will fairly soon
replace all the vertex_cache/prim_queue/shader_queue stuff that's so
hard to understand...
Split the vertex processing into a couple of distinct stages:
- Frontend
- Prepares two lists of elements (fetch and draw) to be processed
by the next stage. This stage doesn't fetch or draw vertices, but
makes the decision which to draw. Multiple implementations of this
will implement different strategies, currently just a vcache
implementation.
- MiddleEnd
- Takes the list of fetch elements, fetches them, runs the vertex
shader, cliptest, viewport transform on them to produce a
linear array of vertex_header vertices.
- Passes that list of vertices, plus the draw_elements (which index
into that list) onto the backend
- Backend
- Either the existing primitive/clipping pipeline, or the vbuf_render
hardware backend provided by the driver.
Currently, the middle-end is the old passthrough code, and it build hardware
vertices, not vertex_header vertices as above. It may be that passthrough
is a special case in this respect.
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