[Mesa-dev] [PATCH 2/2] Revert "i965: Implement guardband clipping on Ivybridge."

[Oliver McFadden]

This reverts commit 610910a66d1a97ca51ad8a003bdeadfe9563d721.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=55523
Signed-off-by: Oliver McFadden <oliver.mcfadden at linux.intel.com>
CC: Kenneth Graunke <kenneth at whitecape.org>
---
v1: note that I have not actually verified this bug exists on IvyBridge, however
given the severity of the bug (major rendering errors in prominent benchmark
applications) I believe it's safer to simply revert both on master and all
stable/release branches.  I am open for discussion on this second patch.

I have verified that SandyBridge suffers badly from this bug on multiple OpenGL
ES2.0 programs/benchmarks.

 src/mesa/drivers/dri/i965/gen7_clip_state.c     |    1 -
 src/mesa/drivers/dri/i965/gen7_viewport_state.c |   19 +++++--------------
 2 files changed, 5 insertions(+), 15 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen7_clip_state.c b/src/mesa/drivers/dri/i965/gen7_clip_state.c
index 3bc6de0..15de042 100644
--- a/src/mesa/drivers/dri/i965/gen7_clip_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_clip_state.c
@@ -101,7 +101,6 @@ upload_clip_state(struct brw_context *brw)
 	     GEN6_CLIP_MODE_NORMAL |
              nonperspective_barycentric_enable_flag |
 	     GEN6_CLIP_XY_TEST |
-	     GEN6_CLIP_GB_TEST |
 	     userclip << GEN6_USER_CLIP_CLIP_DISTANCES_SHIFT |
 	     depth_clamp |
 	     provoking);
diff --git a/src/mesa/drivers/dri/i965/gen7_viewport_state.c b/src/mesa/drivers/dri/i965/gen7_viewport_state.c
index 7036ef6..2bcf338 100644
--- a/src/mesa/drivers/dri/i965/gen7_viewport_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_viewport_state.c
@@ -43,20 +43,11 @@ gen7_upload_sf_clip_viewport(struct brw_context *brw)
    /* Also assign to clip.vp_offset in case something uses it. */
    brw->clip.vp_offset = brw->sf.vp_offset;
 
-   /* According to the "Vertex X,Y Clamping and Quantization" section of the
-    * Strips and Fans documentation, Ivybridge and later don't have a maximum
-    * post-clamp delta.  However, the guardband extent must fit in [-32K, 32K)
-    * which gives us a maximum size of 64K.  Use 65000 rather than 65536 to be
-    * somewhat cautious---make the guardband slightly smaller than the maximum.
-    */
-   const float maximum_guardband_extent = 65000;
-   float gbx = maximum_guardband_extent / (float) ctx->Viewport.Width;
-   float gby = maximum_guardband_extent / (float) ctx->Viewport.Height;
-
-   vp->guardband.xmin = -gbx;
-   vp->guardband.xmax = gbx;
-   vp->guardband.ymin = -gby;
-   vp->guardband.ymax = gby;
+   /* Disable guardband clipping (see gen6_viewport_state.c for rationale). */
+   vp->guardband.xmin = -1.0;
+   vp->guardband.xmax = 1.0;
+   vp->guardband.ymin = -1.0;
+   vp->guardband.ymax = 1.0;
 
    /* _NEW_BUFFERS */
    if (render_to_fbo) {
-- 
1.7.8.6