[Mesa-dev] [RFC] gallium: add support for rectangle primitives

[Jose Fonseca]

On 21/08/14 17:59, Roland Scheidegger wrote:
> Am 21.08.2014 18:44, schrieb Marek Olšák:
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> This is already supported by r600g and radeonsi.
>> Alex suggested this could be useful for video acceleration state trackers.
>> ---
>>   src/gallium/auxiliary/tgsi/tgsi_strings.c     | 3 ++-
>>   src/gallium/auxiliary/util/u_prim.h           | 1 +
>>   src/gallium/docs/source/screen.rst            | 6 ++++++
>>   src/gallium/drivers/r600/r600_pipe.c          | 1 +
>>   src/gallium/drivers/radeon/r600_pipe_common.h | 2 +-
>>   src/gallium/drivers/radeonsi/si_pipe.c        | 1 +
>>   src/gallium/include/pipe/p_defines.h          | 4 +++-
>>   7 files changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_strings.c b/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> index 3c108a8..ddc23c1 100644
>> --- a/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> +++ b/src/gallium/auxiliary/tgsi/tgsi_strings.c
>> @@ -164,7 +164,8 @@ const char *tgsi_primitive_names[PIPE_PRIM_MAX] =
>>      "LINES_ADJACENCY",
>>      "LINE_STRIP_ADJACENCY",
>>      "TRIANGLES_ADJACENCY",
>> -   "TRIANGLE_STRIP_ADJACENCY"
>> +   "TRIANGLE_STRIP_ADJACENCY",
>> +   "RECTANGLES"
>>   };
>>
>>   const char *tgsi_fs_coord_origin_names[2] =
>> diff --git a/src/gallium/auxiliary/util/u_prim.h b/src/gallium/auxiliary/util/u_prim.h
>> index cf1a18f..d631dc1 100644
>> --- a/src/gallium/auxiliary/util/u_prim.h
>> +++ b/src/gallium/auxiliary/util/u_prim.h
>> @@ -131,6 +131,7 @@ u_prim_vertex_count(unsigned prim)
>>         { 4, 1 }, /* PIPE_PRIM_LINE_STRIP_ADJACENCY */
>>         { 6, 6 }, /* PIPE_PRIM_TRIANGLES_ADJACENCY */
>>         { 6, 2 }, /* PIPE_PRIM_TRIANGLE_STRIP_ADJACENCY */
>> +      { 3, 3 }  /* PIPE_PRIM_RECTANGLES */
>>      };
>>
>>      return (likely(prim < PIPE_PRIM_MAX)) ? &prim_table[prim] : NULL;
>> diff --git a/src/gallium/docs/source/screen.rst b/src/gallium/docs/source/screen.rst
>> index eee254e..f162ec0 100644
>> --- a/src/gallium/docs/source/screen.rst
>> +++ b/src/gallium/docs/source/screen.rst
>> @@ -26,6 +26,12 @@ The integer capabilities:
>>     normalized coordinates, and mipmaps.
>>   * ``PIPE_CAP_TWO_SIDED_STENCIL``: Whether the stencil test can also affect back-facing
>>     polygons.
>> +* ``PIPE_CAP_PRIM_TYPE_RECTANGLES``: Whether rectangle primitives are supported.
>> +  Rectangles are like quads, but they are only specified by the first 3 vertices.
>> +  The 4th vertex is computed from the first three by hardware. Rectangles must
>> +  be parallel with screen borders, which means they can only be rotated with
>> +  90-degree increments. Rectangles bypass clipping and therefore can be specified
>> +  in screen coordinates.
> Do they also need to be planar (same z for each vertex)?
> Also, the implicit bypass clip / screen coordinate specification makes
> them quite an outlier among all the primitives. Hmm...

Yes, these restrictions would impose a lot of special casing if e.g., 
softpipe/llvmpipe wanted to support these.  And rects are particularly 
interesting for software rasterizers, as they can be rasterized much 
more efficiently.

Does r600g/radeonsi's hardware support for rect impose these 
restrictions? Or could rect be made work more like other primitives?

Jose