Bug 1189715 - report GL_ARB_texture_rg extension to SkiaGL to avoid using GL_ALPHA render targets. r=jgilbert

gfx/gl/GLContext.cpp

@@ -105,6 +105,7 @@ static const char *const sExtensionNames[] = {
     "GL_ARB_texture_float",
     "GL_ARB_texture_non_power_of_two",
     "GL_ARB_texture_rectangle",
+    "GL_ARB_texture_rg",
     "GL_ARB_texture_storage",
     "GL_ARB_texture_swizzle",
     "GL_ARB_timer_query",

gfx/gl/GLContext.h

@@ -138,6 +138,7 @@ enum class GLFeature {
     texture_half_float,
     texture_half_float_linear,
     texture_non_power_of_two,
+    texture_rg,
     texture_storage,
     texture_swizzle,
     transform_feedback2,
@@ -427,6 +428,7 @@ public:
         ARB_texture_float,
         ARB_texture_non_power_of_two,
         ARB_texture_rectangle,
+        ARB_texture_rg,
         ARB_texture_storage,
         ARB_texture_swizzle,
         ARB_timer_query,

gfx/gl/GLContextFeatures.cpp

@@ -690,6 +690,15 @@ static const FeatureInfo sFeatureInfoArr[] = {
             GLContext::Extensions_End
         }
     },
+    {
+        "texture_rg",
+        GLVersion::GL3,
+        GLESVersion::ES3,
+        GLContext::ARB_texture_rg,
+        {
+            GLContext::Extensions_End
+        }
+    },
     {
         "texture_storage",
         GLVersion::GL4_2,

gfx/gl/SkiaGLGlue.cpp

@@ -371,6 +371,10 @@ const GLubyte* glGetString_mozilla(GrGLenum name)
                 } else if (sGLContext.get()->IsExtensionSupported(GLContext::EXT_framebuffer_object)) {
                     strcat(extensionsString, "GL_EXT_framebuffer_object ");
                 }
+
+                if (sGLContext.get()->IsSupported(GLFeature::texture_rg)) {
+                    strcat(extensionsString, "GL_ARB_texture_rg ");
+                }
             }
 
             if (sGLContext.get()->IsExtensionSupported(GLContext::EXT_texture_format_BGRA8888)) {