Re: [Mesa-dev] [PATCH 7/7] i965: Enable ARB_transform_feedback2 on Sandybridge.

[Matt Turner]

On Fri, Feb 17, 2017 at 1:56 AM, Kenneth Graunke  wrote:
> The only feature over and above ES 3.0 is DrawTransformFeedback().
>
> We already have to do the whole SOL_NUM_PRIMS_WRITTEN counter dance in
> order to compute the SVBI value for ResumeTransformFeedback(), at which
> point our existing GetTransformFeedbackVertexCount() implementation will
> do the trick (though with a stall to CPU map the buffer).
>
> Someday, we could probably implement DrawTransformFeedback() more
> efficiently, using the "Load Internal Vertex Count" feature of
> 3DSTATE_SVB_INDEX and the 3DPRIMITIVE indirect vertex count bit.
>
> Rumor has it this allows people to use WebGL 2.0 on Sandybridge.
>
> Note that we don't need pipelined register writes like Gen7+ because
> we use the 3DSTATE_SVB_INDEX command rather than MI_LOAD_REGISTER_MEM.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99842
> Signed-off-by: Kenneth Graunke 

Should update the release notes and features.txt as well.
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[Mesa-dev] [PATCH 7/7] i965: Enable ARB_transform_feedback2 on Sandybridge.

[Kenneth Graunke]

The only feature over and above ES 3.0 is DrawTransformFeedback().

We already have to do the whole SOL_NUM_PRIMS_WRITTEN counter dance in
order to compute the SVBI value for ResumeTransformFeedback(), at which
point our existing GetTransformFeedbackVertexCount() implementation will
do the trick (though with a stall to CPU map the buffer).

Someday, we could probably implement DrawTransformFeedback() more
efficiently, using the "Load Internal Vertex Count" feature of
3DSTATE_SVB_INDEX and the 3DPRIMITIVE indirect vertex count bit.

Rumor has it this allows people to use WebGL 2.0 on Sandybridge.

Note that we don't need pipelined register writes like Gen7+ because
we use the 3DSTATE_SVB_INDEX command rather than MI_LOAD_REGISTER_MEM.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99842
Signed-off-by: Kenneth Graunke 
---
 src/mesa/drivers/dri/i965/brw_context.c  | 2 ++
 src/mesa/drivers/dri/i965/intel_extensions.c | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_context.c 
b/src/mesa/drivers/dri/i965/brw_context.c
index 977c59c1c3e..17800e3fd60 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -483,6 +483,8 @@ brw_init_driver_functions(struct brw_context *brw,
   functions->EndTransformFeedback = brw_end_transform_feedback;
   functions->PauseTransformFeedback = brw_pause_transform_feedback;
   functions->ResumeTransformFeedback = brw_resume_transform_feedback;
+  functions->GetTransformFeedbackVertexCount =
+ brw_get_transform_feedback_vertex_count;
}
 
if (brw->gen >= 6)
diff --git a/src/mesa/drivers/dri/i965/intel_extensions.c 
b/src/mesa/drivers/dri/i965/intel_extensions.c
index f1290bf7b49..ec7ff02be84 100644
--- a/src/mesa/drivers/dri/i965/intel_extensions.c
+++ b/src/mesa/drivers/dri/i965/intel_extensions.c
@@ -158,6 +158,9 @@ intelInitExtensions(struct gl_context *ctx)
   ctx->Extensions.EXT_timer_query = true;
}
 
+   if (brw->gen == 6)
+  ctx->Extensions.ARB_transform_feedback2 = true;
+
if (brw->gen >= 6) {
   ctx->Extensions.ARB_blend_func_extended =
  !driQueryOptionb(>optionCache, "disable_blend_func_extended");
-- 
2.11.1

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