[Mesa-dev] [PATCH 23/23] i965: Skip uploading border color when unnecessary.

[Kenneth Graunke]

The border color is only needed when using the GL_CLAMP_TO_BORDER or
(deprecated) GL_CLAMP wrap modes; all others ignore it, including the
common GL_CLAMP_TO_EDGE and GL_REPEAT wrap modes.

In those cases, we can skip uploading it entirely, saving a bit of space
in the batchbuffer.  Instead, we just point it at the start of the
batch (offset 0); we have to program something, and that address is safe
to read.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_sampler_state.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_sampler_state.c b/src/mesa/drivers/dri/i965/brw_sampler_state.c
index f48e3c9..ad9a527 100644
--- a/src/mesa/drivers/dri/i965/brw_sampler_state.c
+++ b/src/mesa/drivers/dri/i965/brw_sampler_state.c
@@ -161,6 +161,16 @@ translate_wrap_mode(struct brw_context *brw, GLenum wrap, bool using_nearest)
 }
 
 /**
+ * Return true if the given wrap mode requires the border color to exist.
+ */
+static bool
+wrap_mode_needs_border_color(unsigned wrap_mode)
+{
+   return wrap_mode == BRW_TEXCOORDMODE_CLAMP_BORDER ||
+          wrap_mode == GEN8_TEXCOORDMODE_HALF_BORDER;
+}
+
+/**
  * Upload SAMPLER_BORDER_COLOR_STATE.
  */
 static void
@@ -410,8 +420,16 @@ brw_update_sampler_state(struct brw_context *brw,
                       lod_bits);
    base_level = U_FIXED(0, 1);
 
-   uint32_t border_color_offset;
-   upload_default_color(brw, sampler, unit, &border_color_offset);
+   /* Upload the border color if necessary.  If not, just point it at
+    * offset 0 (the start of the batch) - the color should be ignored,
+    * but that address won't fault in case something reads it anyway.
+    */
+   uint32_t border_color_offset = 0;
+   if (wrap_mode_needs_border_color(wrap_s) ||
+       wrap_mode_needs_border_color(wrap_t) ||
+       wrap_mode_needs_border_color(wrap_r)) {
+      upload_default_color(brw, sampler, unit, &border_color_offset);
+   }
 
    brw_emit_sampler_state(brw,
                           sampler_state,
-- 
2.0.2