[Mesa-dev] [PATCH 6/7] i965/blorp: Rework sRGB override behavior.

[Kenneth Graunke]

The previous code for sRGB overrides assumes that the source and
destination formats are equal, other than the color space.  This won't
be feasible when we add support for format conversions.

Here are a few cases, and how the old code handled them:

1.  RGB8 -> SRGB8, MSAA     ==>   SRGB8 -> SRGB8
2.  RGB8 -> SRGB8, single   ==>    RGB8 -> RGB8
3. SRGB8 ->  RGB8, MSAA     ==>    RGB8 -> RGB8
4. SRGB8 ->  RGB8, single   ==>   SRGB8 -> SRGB8

Apparently, preserving the behavior of #1 is important.  When doing a
multisample to single-sample resolve, blending the samples together in
an sRGB correct fashion results in a noticably higher quality image.
It also is necessary to pass Piglit's EXT_framebuffer_multisample
accuracy color tests.

Paul, Eric, Anuj, and I talked about this, and aren't sure that it
matters in the other cases.

This patch preserves the behavior of #1, but otherwise reverts to
doing everything in linear space, changing the behavior of case #4.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_blorp.cpp      | 10 ++++++----
 src/mesa/drivers/dri/i965/brw_blorp_blit.cpp | 14 +++++++++-----
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_blorp.cpp b/src/mesa/drivers/dri/i965/brw_blorp.cpp
index c59bb66..91df346 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp.cpp
@@ -104,15 +104,17 @@ brw_blorp_surface_info::set(struct brw_context *brw,
    case MESA_FORMAT_Z16:
       this->brw_surfaceformat = BRW_SURFACEFORMAT_R16_UNORM;
       break;
-   default:
+   default: {
+      gl_format linear_format = _mesa_get_srgb_format_linear(mt->format);
       if (is_render_target) {
-         assert(brw->format_supported_as_render_target[mt->format]);
-         this->brw_surfaceformat = brw->render_target_format[mt->format];
+         assert(brw->format_supported_as_render_target[linear_format]);
+         this->brw_surfaceformat = brw->render_target_format[linear_format];
       } else {
-         this->brw_surfaceformat = brw_format_for_mesa_format(mt->format);
+         this->brw_surfaceformat = brw_format_for_mesa_format(linear_format);
       }
       break;
    }
+   }
 }
 
 
diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
index f581871..2427085 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
@@ -2077,13 +2077,17 @@ brw_blorp_blit_params::brw_blorp_blit_params(struct brw_context *brw,
     * proprietary OpenGL driver also follow this approach. So, we choose to
     * follow it in our driver.
     *
-    * Following if-else block takes care of this exception made for
-    * multisampled resolves.
+    * When multisampling, if the source and destination formats are equal
+    * (aside from the color space), we choose to blit in sRGB space to get
+    * this higher quality image.
     */
-   if (src.num_samples > 1)
+   if (src.num_samples > 1 &&
+       _mesa_get_format_color_encoding(dst_mt->format) == GL_SRGB &&
+       _mesa_get_srgb_format_linear(src_mt->format) ==
+       _mesa_get_srgb_format_linear(dst_mt->format)) {
+      dst.brw_surfaceformat = brw_format_for_mesa_format(dst_mt->format);
       src.brw_surfaceformat = dst.brw_surfaceformat;
-   else
-      dst.brw_surfaceformat = src.brw_surfaceformat;
+   }
 
    use_wm_prog = true;
    memset(&wm_prog_key, 0, sizeof(wm_prog_key));
-- 
1.8.3.2