[Mesa-dev] [PATCH v2 2/2] i965/cnl: Correctly sample from fast-cleared sRGB textures

[Nanley Chery]

When sampling from fast-cleared sRGB textures on gen10, the hardware
will not decode the clear color to linear. We must therefore do it in
software.

This makes the following piglit tests pass:
* spec at arb_framebuffer_srgb@arb_framebuffer_srgb-fast-clear-blend
* spec at arb_framebuffer_srgb@fbo-fast-clear
* spec at arb_framebuffer_srgb@msaa-fast-clear
* spec at ext_texture_srgb@fbo-fast-clear
* spec at ext_texture_srgb@multisample-fast-clear gl_ext_texture_srgb

v2 (Jason Ekstrand):
- Update some comments.
- Simplify assertions.
- Use an sRGB-to-linear helper.

Signed-off-by: Nanley Chery <nanley.g.chery at intel.com>
---
 src/mesa/drivers/dri/i965/brw_blorp.c            |  7 +++++++
 src/mesa/drivers/dri/i965/brw_meta_util.c        | 26 ++++++++++++++++++++++++
 src/mesa/drivers/dri/i965/brw_meta_util.h        |  5 +++++
 src/mesa/drivers/dri/i965/brw_wm_surface_state.c |  9 +++++++-
 4 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_blorp.c b/src/mesa/drivers/dri/i965/brw_blorp.c
index 38284d3b85..b10e9b95b7 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp.c
+++ b/src/mesa/drivers/dri/i965/brw_blorp.c
@@ -328,6 +328,13 @@ brw_blorp_blit_miptrees(struct brw_context *brw,
    struct blorp_surf src_surf, dst_surf;
    blorp_surf_for_miptree(brw, &src_surf, src_mt, src_aux_usage, false,
                           &src_level, src_layer, 1, &tmp_surfs[0]);
+   if (devinfo->gen >= 10 && isl_format_is_srgb(src_isl_format) &&
+       src_clear_supported) {
+      src_surf.clear_color =
+         gen10_convert_srgb_fast_clear_color(devinfo, src_isl_format,
+                                             src_mt->fast_clear_color);
+   }
+
    blorp_surf_for_miptree(brw, &dst_surf, dst_mt, dst_aux_usage, true,
                           &dst_level, dst_layer, 1, &tmp_surfs[1]);
 
diff --git a/src/mesa/drivers/dri/i965/brw_meta_util.c b/src/mesa/drivers/dri/i965/brw_meta_util.c
index d292f5a8e2..d1ce9d46ea 100644
--- a/src/mesa/drivers/dri/i965/brw_meta_util.c
+++ b/src/mesa/drivers/dri/i965/brw_meta_util.c
@@ -315,6 +315,32 @@ brw_is_color_fast_clear_compatible(struct brw_context *brw,
    return true;
 }
 
+/* When sampling from fast-cleared sRGB textures on gen10, the hardware
+ * will not decode the clear color to linear. We must therefore do it in
+ * software.
+ */
+union isl_color_value
+gen10_convert_srgb_fast_clear_color(const struct gen_device_info *devinfo,
+                                    enum isl_format format,
+                                    const union isl_color_value color)
+{
+   /* Gen10 supports fast-clearing three of GL's sRGB formats. */
+   assert(devinfo->gen >= 10);
+   assert(format == ISL_FORMAT_R8G8B8A8_UNORM_SRGB ||
+          format == ISL_FORMAT_B8G8R8A8_UNORM_SRGB ||
+          format == ISL_FORMAT_B8G8R8X8_UNORM_SRGB);
+
+   /* According to do_single_blorp_clear(), fast-clears for texture-views are
+    * disabled. This means that we only have to do channel-to-channel format
+    * conversions.
+    */
+   union isl_color_value override_color = color;
+   for (unsigned i = 0; i < 3; i++)
+      override_color.f32[i] = util_format_srgb_to_linear_float(color.f32[i]);
+
+   return override_color;
+}
+
 /**
  * Convert the given color to a bitfield suitable for ORing into DWORD 7 of
  * SURFACE_STATE (DWORD 12-15 on SKL+).
diff --git a/src/mesa/drivers/dri/i965/brw_meta_util.h b/src/mesa/drivers/dri/i965/brw_meta_util.h
index 4b3408df15..ee0b3bd3e1 100644
--- a/src/mesa/drivers/dri/i965/brw_meta_util.h
+++ b/src/mesa/drivers/dri/i965/brw_meta_util.h
@@ -42,6 +42,11 @@ brw_meta_mirror_clip_and_scissor(const struct gl_context *ctx,
                                  GLfloat *dstX1, GLfloat *dstY1,
                                  bool *mirror_x, bool *mirror_y);
 
+union isl_color_value
+gen10_convert_srgb_fast_clear_color(const struct gen_device_info *devinfo,
+                                    enum isl_format format,
+                                    const union isl_color_value color);
+
 union isl_color_value
 brw_meta_convert_fast_clear_color(const struct brw_context *brw,
                                   const struct intel_mipmap_tree *mt,
diff --git a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
index adf60a840b..315b96e9c4 100644
--- a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
+++ b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
@@ -51,6 +51,7 @@
 #include "intel_buffer_objects.h"
 
 #include "brw_context.h"
+#include "brw_meta_util.h"
 #include "brw_state.h"
 #include "brw_defines.h"
 #include "brw_wm.h"
@@ -174,7 +175,13 @@ brw_emit_surface_state(struct brw_context *brw,
       /* We only really need a clear color if we also have an auxiliary
        * surface.  Without one, it does nothing.
        */
-      clear_color = mt->fast_clear_color;
+      if (devinfo->gen >= 10 && isl_format_is_srgb(view.format)) {
+         clear_color =
+            gen10_convert_srgb_fast_clear_color(devinfo, view.format,
+                                                mt->fast_clear_color);
+      } else {
+         clear_color = mt->fast_clear_color;
+      }
    }
 
    void *state = brw_state_batch(brw,
-- 
2.15.0