On Fri, Aug 13, 2010 at 10:51 PM, Keith Whitwell <kei...@vmware.com> wrote: > On Fri, 2010-08-13 at 07:46 -0700, Chia-I Wu wrote: >> On Fri, Aug 13, 2010 at 10:14 PM, Keith Whitwell <kei...@vmware.com> wrote: >> > On Fri, 2010-08-13 at 07:04 -0700, Chia-I Wu wrote: >> >> Hi, >> >> >> >> There are two primitive transformations in gallium draw module. In >> >> varray, primitives are "split"ted. When a primitive has more vertices >> >> than the middle end can handle, varray splits the primitive and calls >> >> the middle end multiple times. >> >> >> >> In vcache, primitives are "decompose"d. More advanced primitives are >> >> decomposed into one of point, line(_adj), or triangle(_adj). >> >> Similarly, vcache may call the middle end multiple times to flush its >> >> internal buffer. In some cases, vcache passes the primitves through >> >> without decomposing nor splitting, as can be seen in vcache_check_run. >> >> >> >> The issue with vcache is that it has to decompose a primitive >> >> differently depending on the provoking convention, as explained in >> >> >> >> http://lists.freedesktop.org/archives/mesa-dev/2010-August/001797.html >> >> >> >> It becomes a problem when GS is active. >> >> >> >> My proposal is to make vcache split instead of decompose. Because >> >> varray only splits and vcache has a pass-through path, the rest of the >> >> workflow already has to support all primitive types. Switching from >> >> decompose to split does not require a big change to the rest of the >> >> workflow. >> >> >> >> But then vcache will look a lot like varray, only with indexed >> >> primitive support. It leads me to a new frontend that replaces both >> >> varray and vcache: vsplit >> >> >> >> http://cgit.freedesktop.org/~olv/mesa/log/?h=draw-vsplit >> >> >> >> vsplit is based on varray. It uses some code from vcache to support >> >> indexed primitives. When vcache decomposes, there are flags being set >> >> to indicate that if the stipple counter should be reset or if some >> >> edge of a triangle should be omitted in unfilled mode. The segments >> >> of a splitted primitive have flags for similar purposes too: >> >> >> >> DRAW_SPLIT_AFTER More segments to come after this one >> >> DRAW_SPLIT_BEFORE There are preceding segments >> >> >> >> These flags are set by vsplit and the middle ends pass them to the >> >> other stages. Therefore, the run methods of middle ends are augmented >> >> to take the flags. >> >> >> >> To summarize, vsplit >> >> >> >> - fixes GS when (flatshade && flatshade_first) is on >> >> - never sends more vertices than the middle end claims to handle >> >> - is faster than vcache: split instead of decompose, no get_elt >> >> calls >> >> - no longer uses the higher bits of draw_elts for stipple/edge flags >> >> >> >> Suggestions? >> > >> > >> > Hi - I haven't looked at the patches yet, but a couple of questions: >> > >> > How does this interact with the draw_pipe_* code - which requires >> > decomposed primitives? >> draw_pipe.c decomposes the primitives. It is there before because it >> has to support varray and vcache_check_run which do not decompose. > > OK. > >> > How does this cope with indexed rendering where the vertex buffers >> > themselves are too large (for hardware or some other entity)? Eg. >> > imagine the hardware could cope with up to 64k vertices, and you have a >> > drawelements call randomly referencing vertices in range 0..128k ? >> Vertex fetching happens in the middle end so the range of the indices >> is not a problem. Though vsplit guarantees that it never calls the >> middle end with more vertices than the middle end claims to support >> (as returned by draw_pt_middle_end::prepare). The limit is usually >> decidied by the size of the buffer for vertex emitting. > > I guess I'm wondering how it does this. If the middle end says it > supports 64k vertices, and the vertex element looks like > > [0, 128k, 64k, 32k, 96k, 16k, 1, ... ] > > what gets sent? (Sorry, I still haven't looked at the code, you could > well have addressed this). I see. The frontend would set
fetch_elts = [0, 128k, 64k, 32k, 96k, 16k, 1, ... ] draw_elts = [0, 1, 2, 3, 4, 5, 6, ...] fetch_elts is processed by the middle end and it will fetch the given vertices. draw_elts will be passed to draw_emit or the pipeline. It is the new index buffer, which indexes into the fetched vertices. It is actual the same as vcache. So when fetch_elts is [0, 128k, 64k, 64k, 128k, 16k, ...], draw_elts would be set to [0, 1, 2, 2, 1, 3, ...] The number of elements to fetch (and shade) is minimized. -- o...@lunarg.com _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
