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). Keith _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
