Bug 579276. Part 6: Add gfxASurface::GetTextQualityInTransparentSurfaces API. r=jrmuizel,sr=vlad

gfx/thebes/gfxASurface.h

@@ -156,6 +156,39 @@ public:
         return PR_TRUE;
     }
 
+    enum TextQuality {
+        /**
+         * TEXT_QUALITY_OK means that text is always rendered to a
+         * transparent surface just as well as it would be rendered to an
+         * opaque surface. This would normally only be true if
+         * subpixel antialiasing is disabled or if the platform's
+         * transparent surfaces support component alpha.
+         */
+        TEXT_QUALITY_OK,
+        /**
+         * TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS means that text is rendered
+         * to a transparent surface just as well as it would be rendered to an
+         * opaque surface, but only if all the pixels the text is drawn
+         * over already have opaque alpha values.
+         */
+        TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS,
+        /**
+         * TEXT_QUALITY_BAD means that text is rendered
+         * to a transparent surface worse than it would be rendered to an
+         * opaque surface, even if all the pixels the text is drawn
+         * over already have opaque alpha values.
+         */
+        TEXT_QUALITY_BAD
+    };
+    /**
+     * Determine how well text would be rendered in transparent surfaces that
+     * are similar to this surface.
+     */
+    virtual TextQuality GetTextQualityInTransparentSurfaces()
+    {
+        return TEXT_QUALITY_BAD;
+    }
+
     int CairoStatus();
 
     /* Make sure that the given dimensions don't overflow a 32-bit signed int

gfx/thebes/gfxD2DSurface.h

@@ -57,6 +57,12 @@ public:
 
     virtual ~gfxD2DSurface();
 
+    virtual TextQuality GetTextQualityInTransparentSurfaces()
+    {
+      // D2D always draws text in transparent surfaces with grayscale-AA,
+      // even if the text is over opaque pixels.
+      return TEXT_QUALITY_BAD;
+    }
 
     void Present();
     void Scroll(const nsIntPoint &aDelta, const nsIntRect &aClip);

gfx/thebes/gfxQuartzSurface.h

@@ -60,6 +60,10 @@ public:
     {
       return PR_FALSE;
     }
+    virtual TextQuality GetTextQualityInTransparentSurfaces()
+    {
+      return TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS;
+    }
 
     const gfxSize& GetSize() const { return mSize; }
 

gfx/thebes/gfxWindowsSurface.h

@@ -81,6 +81,11 @@ public:
                                                       const gfxIntSize& size,
                                                       gfxImageFormat format);
 
+    virtual TextQuality GetTextQualityInTransparentSurfaces()
+    {
+      return TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS;
+    }
+
     nsresult BeginPrinting(const nsAString& aTitle, const nsAString& aPrintToFileName);
     nsresult EndPrinting();
     nsresult AbortPrinting();

gfx/thebes/gfxXlibSurface.h

@@ -77,6 +77,11 @@ public:
     virtual already_AddRefed<gfxASurface>
     CreateSimilarSurface(gfxContentType aType, const gfxIntSize& aSize);
 
+    virtual TextQuality GetTextQualityInTransparentSurfaces()
+    {
+      return TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS;
+    }
+
     const gfxIntSize& GetSize() { return mSize; }
 
     Display* XDisplay() { return mDisplay; }