Bug 453726 - thebes does an unnecessary float->byte->float conversion on the alpha channel when color management is turned on. r=vlad

gfx/thebes/src/gfxContext.cpp

@@ -637,7 +637,9 @@ gfxContext::SetColor(const gfxRGBA& c)
                            1);
             gfxRGBA cms(packed, gfxRGBA::PACKED_ARGB);
 #endif
-            cairo_set_source_rgba(mCairo, cms.r, cms.g, cms.b, cms.a);
+            // Use the original alpha to avoid unnecessary float->byte->float
+            // conversion errors
+            cairo_set_source_rgba(mCairo, cms.r, cms.g, cms.b, c.a);
             return;
         }
     }

gfx/thebes/src/gfxPattern.cpp

@@ -103,8 +103,10 @@ gfxPattern::AddColorStop(gfxFloat offset, const gfxRGBA& c)
                            1);
             gfxRGBA cms(packed, gfxRGBA::PACKED_ARGB);
 #endif
+            // Use the original alpha to avoid unnecessary float->byte->float
+            // conversion errors
             cairo_pattern_add_color_stop_rgba(mPattern, offset,
-                                              cms.r, cms.g, cms.b, cms.a);
+                                              cms.r, cms.g, cms.b, c.a);
             return;
         }
     }