EXA/6xx/7xx: accelerate PictOpOver with component alpha

Subpixel text rendering is typically done with a solid src and
a pixmap mask. Traditionally, this cannot be accelerated in a single
pass and requires two passes [1]. However, we can cheat a little
with a constant blend color.

We can use:
const.A = src.A / src.A
const.R = src.R / src.A
const.G = src.G / src.A
const.B = src.B / src.A

dst.A = const.A * (src.A * mask.A) + (1 - (src.A * mask.A)) * dst.A
dst.R = const.R * (src.A * mask.R) + (1 - (src.A * mask.R)) * dst.R
dst.G = const.G * (src.A * mask.G) + (1 - (src.A * mask.G)) * dst.G
dst.B = const.B * (src.A * mask.B) + (1 - (src.A * mask.B)) * dst.B

This only needs a single source value. src.A is cancelled down in
the right places.

[1] http://anholt.livejournal.com/32058.html

r6xx still be used on some machine,
Ported from commit 4375a6e75e5d41139be7031a0dee58c057ecbd07.

Signed-off-by: Tan Hu <tan.hu@zte.com.cn>
Reviewed-by: Grigori Goronzy <greg@chown.ath.cx>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/r6xx_accel.c b/src/r6xx_accel.c
index a97c84b3..1f5c0523 100644
--- a/src/r6xx_accel.c
+++ b/src/r6xx_accel.c
@@ -174,6 +174,20 @@ r600_sq_setup(ScrnInfoPtr pScrn, sq_config_t *sq_conf)
     END_BATCH();
 }
 
+void r600_set_blend_color(ScrnInfoPtr pScrn, float *color)
+{
+    RADEONInfoPtr info = RADEONPTR(pScrn);
+
+    BEGIN_BATCH(2 + 4);
+    PACK0(CB_BLEND_RED, 4);
+    EFLOAT(color[0]); /* R */
+    EFLOAT(color[1]); /* G */
+    EFLOAT(color[2]); /* B */
+    EFLOAT(color[3]); /* A */
+    END_BATCH();
+}
+
+
 void
 r600_set_render_target(ScrnInfoPtr pScrn, cb_config_t *cb_conf, uint32_t domain)
 {