[Mesa-dev] [PATCH] i965: Add a driconf option to disable GL_ARB_blend_func_extended.

[Kenneth Graunke]

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 <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/common/drirc             |  4 ++++
 src/mesa/drivers/dri/common/xmlpool/options.h | 10 ++++++++++
 src/mesa/drivers/dri/intel/intel_extensions.c |  2 +-
 src/mesa/drivers/dri/intel/intel_screen.c     |  3 ++-
 4 files changed, 17 insertions(+), 2 deletions(-)

Really sad to send this out, but I'm not sure what else to do.  I thought
I found an small bit of out-of-spec behavior that they were relying on
which could make things work, but it doesn't...even with my change, the
sun disappears from the sky.

Still need to report this upstream.

diff --git a/src/mesa/drivers/dri/common/drirc b/src/mesa/drivers/dri/common/drirc
index 2d92878..52d8dd7 100644
--- a/src/mesa/drivers/dri/common/drirc
+++ b/src/mesa/drivers/dri/common/drirc
@@ -2,15 +2,19 @@
     <device screen="0" driver="i965">
         <application name="Unigine Sanctuary" executable="Sanctuary">
             <option name="force_glsl_extensions_warn" value="true" />
+            <option name="disable_blend_func_extended" value="true" />
 	</application>
         <application name="Unigine Tropics" executable="Tropics">
             <option name="force_glsl_extensions_warn" value="true" />
+            <option name="disable_blend_func_extended" value="true" />
 	</application>
         <application name="Unigine Heaven (32-bit)" executable="heaven_x86">
             <option name="force_glsl_extensions_warn" value="true" />
+            <option name="disable_blend_func_extended" value="true" />
 	</application>
         <application name="Unigine Heaven (64-bit)" executable="heaven_x64">
             <option name="force_glsl_extensions_warn" value="true" />
+            <option name="disable_blend_func_extended" value="true" />
 	</application>
     </device>
 </driconf>
diff --git a/src/mesa/drivers/dri/common/xmlpool/options.h b/src/mesa/drivers/dri/common/xmlpool/options.h
index 75c887e..a20e3d1 100644
--- a/src/mesa/drivers/dri/common/xmlpool/options.h
+++ b/src/mesa/drivers/dri/common/xmlpool/options.h
@@ -636,3 +636,13 @@ DRI_CONF_OPT_BEGIN(force_glsl_extensions_warn,bool,def) \
         DRI_CONF_DESC(fr,"Force GLSL extension default behavior to 'warn'") \
         DRI_CONF_DESC(sv,"Force GLSL extension default behavior to 'warn'") \
 DRI_CONF_OPT_END
+
+#define DRI_CONF_DISABLE_BLEND_FUNC_EXTENDED(def) \
+DRI_CONF_OPT_BEGIN(disable_blend_func_extended,bool,def) \
+        DRI_CONF_DESC(en,"Disable dual source blending") \
+        DRI_CONF_DESC(de,"Disable dual source blending") \
+        DRI_CONF_DESC(es,"Disable dual source blending") \
+        DRI_CONF_DESC(nl,"Disable dual source blending") \
+        DRI_CONF_DESC(fr,"Disable dual source blending") \
+        DRI_CONF_DESC(sv,"Disable dual source blending") \
+DRI_CONF_OPT_END
diff --git a/src/mesa/drivers/dri/intel/intel_extensions.c b/src/mesa/drivers/dri/intel/intel_extensions.c
index 953b983..78cd550 100755
--- a/src/mesa/drivers/dri/intel/intel_extensions.c
+++ b/src/mesa/drivers/dri/intel/intel_extensions.c
@@ -103,7 +103,7 @@ 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 bcd85e9..67d41c1 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"
-- 
1.7.11.2