i965: Add a driconf option to disable GL_ARB_blend_func_extended.

Unigine Heaven (at least) has a bug where it incorrectly uses the
GL_ARB_blend_func_extended extension.

Dual source blending allows two color outputs per render target;
individual shader outputs can be assigned to be either the first or
second blending input by setting the 'index' via one of two methods:

- An API call: glBindFragDataLocationIndexed()
- The GLSL 'layout' qualifier provided by GL_ARB_explicit_attrib_location

Both of these only work on user defined fragment shader outputs; it's an
error to use either on built-in outputs like gl_FragData.

Unigine uses gl_FragData and gl_FragColor exclusively, and doesn't even
attempt to use either method to set index == 1.  However, it does set
the blending function to SRC1 enums, which requires a fragment shader
output with index == 1 or else rendering is undefined.

In other words, enabling ARB_blend_func_extended causes Unigine to
render incorrectly, resulting in an apparent regression, even though our
driver code (as far as I can tell) is perfectly fine.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50291
Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Chad Versace <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

2 files changed, 3 insertions, 2 deletions

diff --git a/src/mesa/drivers/dri/intel/intel_extensions.c b/src/mesa/drivers/dri/intel/intel_extensions.c
index 844125dc8a5..c2bc0722afa 100755
--- a/src/mesa/drivers/dri/intel/intel_extensions.c
+++ b/src/mesa/drivers/dri/intel/intel_extensions.c
@@ -104,7 +104,7 @@ intelInitExtensions(struct gl_context *ctx)
       ctx->Extensions.EXT_transform_feedback = true;
 
    if (intel->gen >= 6) {
-      ctx->Extensions.ARB_blend_func_extended = true;
+      ctx->Extensions.ARB_blend_func_extended = !driQueryOptionb(&intel->optionCache, "disable_blend_func_extended");
       ctx->Extensions.ARB_draw_buffers_blend = true;
    }
 
diff --git a/src/mesa/drivers/dri/intel/intel_screen.c b/src/mesa/drivers/dri/intel/intel_screen.c
index e52bf13cfb6..81953ce9334 100644
--- a/src/mesa/drivers/dri/intel/intel_screen.c
+++ b/src/mesa/drivers/dri/intel/intel_screen.c
@@ -79,6 +79,7 @@ PUBLIC const char __driConfigOptions[] =
      DRI_CONF_ALWAYS_FLUSH_BATCH(false)
      DRI_CONF_ALWAYS_FLUSH_CACHE(false)
      DRI_CONF_FORCE_GLSL_EXTENSIONS_WARN(false)
+     DRI_CONF_DISABLE_BLEND_FUNC_EXTENDED(false)
 
       DRI_CONF_OPT_BEGIN(stub_occlusion_query, bool, false)
 	 DRI_CONF_DESC(en, "Enable stub ARB_occlusion_query support on 915/945.")
@@ -90,7 +91,7 @@ PUBLIC const char __driConfigOptions[] =
    DRI_CONF_SECTION_END
 DRI_CONF_END;
 
-const GLuint __driNConfigOptions = 14;
+const GLuint __driNConfigOptions = 15;
 
 #include "intel_batchbuffer.h"
 #include "intel_buffers.h"