1 files changed, 31 insertions, 0 deletions
diff --git a/src/mesa/drivers/dri/i965/gen6_clip_state.c b/src/mesa/drivers/dri/i965/gen6_clip_state.c
index e8c1b915172..ab0828135be 100644
--- a/src/mesa/drivers/dri/i965/gen6_clip_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_clip_state.c
@@ -98,6 +98,37 @@ upload_clip_state(struct brw_context *brw)
 
    dw2 |= GEN6_CLIP_GB_TEST;
 
+   /* We need to disable guardband clipping if the guardband (which we always
+    * program to the maximum screen-space bounding box of 8K x 8K) will be
+    * smaller than the viewport.
+    *
+    * Closely examining the clip determination formulas in the documentation
+    * reveals that objects will be discarded entirely if they're outside the
+    * (small) guardband, even if they're within the (large) viewport:
+    *
+    *     TR = TR_GB || TR_VPXY || TR_VPZ || TR_UC || TR_NEGW
+    *     TA   = !TR && TA_GB && TA_VPZ && TA_NEGW
+    *     MC = !(TA || TR)
+    *
+    * (TA is "Trivial Accept", TR is "Trivial Reject", MC is "Must Clip".)
+    *
+    * Disabling guardband clipping removes the TR_GB condition, which means
+    * they'll be considered MC ("Must Clip") unless they're rejected for
+    * some other reason.
+    *
+    * Note that there is no TA_VPXY condition.  If there were, objects entirely
+    * inside a 16384x16384 viewport would be trivially accepted, breaking the
+    * "objects must have a screenspace bounding box not exceeding 8K in the X
+    * or Y direction" restriction.  Instead, they're clipped.
+    */
+   for (unsigned i = 0; i < ctx->Const.MaxViewports; i++) {
+      if (ctx->ViewportArray[i].Width > 8192 ||
+          ctx->ViewportArray[i].Height > 8192) {
+         dw2 &= ~GEN6_CLIP_GB_TEST;
+         break;
+      }
+   }
+
    /* If the viewport dimensions are smaller than the drawable dimensions,
     * we have to disable guardband clipping prior to Gen8.  We always program
     * the guardband to a fixed size, which is almost always larger than the