[Mesa-dev] [PATCH] i965/blorp: do not use unnecessary hw-blending support

[Topi Pohjolainen]

This is really not needed as blorp blit programs already sample
XRGB normally and get alpha channel set to 1.0 automatically by
the sampler engine. This is simply copied directly to the payload
of the render target write message and hence there is no need for
any additional blending support from the pixel processing pipeline.

Fixes recently modified piglit test gl-3.2-layered-rendering-blit
on IVB. No regressions on IVB.

This is effectively revert of c0554141a9b831b4e614747104dcbbe0fe489b9d:

    i965/blorp: Support overriding destination alpha to 1.0.

    Currently, Blorp requires the source and destination formats to be
    equal.  However, we'd really like to be able to blit between XRGB and
    ARGB formats; our BLT engine paths have supported this for a long time.

    For ARGB -> XRGB, nothing needs to occur: the missing alpha is already
    interpreted as 1.0.  For XRGB -> ARGB, we need to smash the alpha
    channel to 1.0 when writing the destination colors.  This is fairly
    straightforward with blending.

    For now, this code is never used, as the source and destination formats
    still must be equal.  The next patch will relax that restriction.

    NOTE: This is a candidate for the 9.1 branch.

CC: Ian Romanick <ian.d.romanick at intel.com>
CC: Kenneth Graunke <kenneth at whitecape.org>
CC: Martin Steigerwald <martin at lichtvoll.de>
Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
---
 src/mesa/drivers/dri/i965/gen6_blorp.cpp | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen6_blorp.cpp b/src/mesa/drivers/dri/i965/gen6_blorp.cpp
index 90b9fbb..4222fa8 100644
--- a/src/mesa/drivers/dri/i965/gen6_blorp.cpp
+++ b/src/mesa/drivers/dri/i965/gen6_blorp.cpp
@@ -254,26 +254,6 @@ gen6_blorp_emit_blend_state(struct brw_context *brw,
    blend->blend1.write_disable_b = params->color_write_disable[2];
    blend->blend1.write_disable_a = params->color_write_disable[3];
 
-   /* When blitting from an XRGB source to a ARGB destination, we need to
-    * interpret the missing channel as 1.0.  Blending can do that for us:
-    * we simply use the RGB values from the fragment shader ("source RGB"),
-    * but smash the alpha channel to 1.
-    */
-   if (params->src.mt &&
-       _mesa_get_format_bits(params->dst.mt->format, GL_ALPHA_BITS) > 0 &&
-       _mesa_get_format_bits(params->src.mt->format, GL_ALPHA_BITS) == 0) {
-      blend->blend0.blend_enable = 1;
-      blend->blend0.ia_blend_enable = 1;
-
-      blend->blend0.blend_func = BRW_BLENDFUNCTION_ADD;
-      blend->blend0.ia_blend_func = BRW_BLENDFUNCTION_ADD;
-
-      blend->blend0.source_blend_factor = BRW_BLENDFACTOR_SRC_COLOR;
-      blend->blend0.dest_blend_factor = BRW_BLENDFACTOR_ZERO;
-      blend->blend0.ia_source_blend_factor = BRW_BLENDFACTOR_ONE;
-      blend->blend0.ia_dest_blend_factor = BRW_BLENDFACTOR_ZERO;
-   }
-
    return cc_blend_state_offset;
 }
 
-- 
1.8.3.1