0005-drivers-dri-i965-gen6-Clamp-scissor-state-instead-of.patch

From d99d3a8a4cbede67d02c13149f1a090c170ba127 Mon Sep 17 00:00:00 2001
From: Corbin Simpson <simpsoco@chromium.org>
Date: Thu, 28 Aug 2014 14:48:31 -0700
Subject: [PATCH 05/13] drivers/dri/i965/gen6: Clamp scissor state instead of
 truncating.

Replaces one undefined behavior with another, slightly more friendly,
undefined behavior.

BUG=chromium:360217
TEST=Watched some Youtube on Link; can't reproduce original bug as reported.

Change-Id: I7ae0e053ffb6c7a57cb7b3232d27700b6703b3ff
Signed-off-by: Corbin Simpson <simpsoco@chromium.org>
---
 src/mesa/drivers/dri/i965/gen6_scissor_state.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen6_scissor_state.c b/src/mesa/drivers/dri/i965/gen6_scissor_state.c
index 6b01cd1..1d52e95 100644
--- a/src/mesa/drivers/dri/i965/gen6_scissor_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_scissor_state.c
@@ -32,6 +32,13 @@
 #include "main/fbobject.h"
 #include "main/framebuffer.h"

+/* Clamp scissors to 16-bit unsigned values; otherwise, the compiler truncates
+ * them to fit inside the bitfields, which is often not what is desired.
+ * My reading of GL and GLES specs suggests that overly-large scissor values are
+ * not an erroring condition and that the actual behavior is undefined, so
+ * switching from truncation to clamping is probably not a problem. ~ C. */
+#define CLAMP_SCISSOR(X) CLAMP(X, 0x0000, 0xffff)
+
 static void
 gen6_upload_scissor_state(struct brw_context *brw)
 {
@@ -71,17 +78,17 @@ gen6_upload_scissor_state(struct brw_context *brw)
          scissor[i].ymax = 0;
       } else if (render_to_fbo) {
          /* texmemory: Y=0=bottom */
-         scissor[i].xmin = bbox[0];
-         scissor[i].xmax = bbox[1] - 1;
-         scissor[i].ymin = bbox[2];
-         scissor[i].ymax = bbox[3] - 1;
+         scissor[i].xmin = CLAMP_SCISSOR(bbox[0]);
+         scissor[i].xmax = CLAMP_SCISSOR(bbox[1] - 1);
+         scissor[i].ymin = CLAMP_SCISSOR(bbox[2]);
+         scissor[i].ymax = CLAMP_SCISSOR(bbox[3] - 1);
       }
       else {
          /* memory: Y=0=top */
-         scissor[i].xmin = bbox[0];
-         scissor[i].xmax = bbox[1] - 1;
-         scissor[i].ymin = ctx->DrawBuffer->Height - bbox[3];
-         scissor[i].ymax = ctx->DrawBuffer->Height - bbox[2] - 1;
+         scissor[i].xmin = CLAMP_SCISSOR(bbox[0]);
+         scissor[i].xmax = CLAMP_SCISSOR(bbox[1] - 1);
+         scissor[i].ymin = CLAMP_SCISSOR(ctx->DrawBuffer->Height - bbox[3]);
+         scissor[i].ymax = CLAMP_SCISSOR(ctx->DrawBuffer->Height - bbox[2] - 1);
       }
    }
    BEGIN_BATCH(2);
--
1.9.1