etnaviv: fix non-alpha mask composite operations

The composite operation is defined to be:

	(src IN mask) OP dst

The IN operation is: Fa = A(mask), Fb = 0, which gives an equation of:

	C = C(src) * A(mask) + C(mask) * 0

When the mask has no alpha channel, A(mask) is defined to be 1.0, so
this becomes:

	C = C(src)

meaning that the resulting composite operation becomes:

	src OP dst

We can make use of the more efficient etnaviv_accel_composite_srconly()
path to perform this operation as it has no dependency on the mask.

This fixes this rendercheck failure on GC600:
Src composite test error of 255.0000 at (1, 0) --
           R     G     B     A
got:       0.000 0.000 0.000 0.000
expected:  1.000 1.000 1.000 1.000
src color: 1.00 1.00 1.00 1.00
msk color: 1.00 1.00 1.00 1.00
dst color: 1.00 1.00 1.00 1.00
src: 1x1R a8r8g8b8, mask: 10x10 x8r8g8b8, dst: a8r8g8b8

and this failure on GC320:
Src composite test error of 255.0000 at (1, 3) --
           R     G     B     A
got:       0.000 0.000 0.000 0.000
expected:  1.000 1.000 1.000 1.000
src color: 1.00 1.00 1.00 1.00
msk color: 1.00 1.00 1.00 1.00
dst color: 1.00 1.00 1.00 1.00
src: 10x10 x8r8g8b8, mask: 10x10 x8r8g8b8, dst: a8r8g8b8

Signed-off-by: Russell King <rmk@armlinux.org.uk>

1 files changed, 7 insertions, 0 deletions

diff --git a/etnaviv/etnaviv_render.c b/etnaviv/etnaviv_render.c
index 0fb3ac9..ffefc12 100644
--- a/etnaviv/etnaviv_render.c
+++ b/etnaviv/etnaviv_render.c
@@ -745,6 +745,13 @@ static Bool etnaviv_accel_reduce_mask(struct etnaviv_blend_op *final_blend,
 	uint32_t colour;
 
 	/*
+	 * If the mask has no alpha, then the alpha channel is treated
+	 * as constant 1.0.  This makes the IN operation redundant.
+	 */
+	if (!PICT_FORMAT_A(pMask->format) && !pMask->componentAlpha)
+		return TRUE;
+
+	/*
 	 * A PictOpOver with a mask looks like this:
 	 *
 	 *  dst.A = src.A * mask.A + dst.A * (1 - src.A * mask.A)