b=371867, optimize same-color images, r=stuart

gfx/src/thebes/nsThebesImage.cpp

@@ -231,30 +231,57 @@ nsThebesImage::Optimize(nsIDeviceContext* aContext)
     if (mOptSurface || mSinglePixel)
         return NS_OK;
 
-    if (mWidth == 1 && mHeight == 1) {
-        // yeah, let's optimize this.
-        if (mFormat == gfxImageSurface::ImageFormatARGB32 ||
-            mFormat == gfxImageSurface::ImageFormatRGB24)
-        {
-            PRUint32 pixel = *((PRUint32 *) mImageSurface->Data());
+    /* Figure out if the entire image is a constant color */
 
-            mSinglePixelColor = gfxRGBA
-                (pixel,
-                 (mFormat == gfxImageSurface::ImageFormatRGB24 ?
-                  gfxRGBA::PACKED_XRGB :
-                  gfxRGBA::PACKED_ARGB_PREMULTIPLIED));
+    // this should always be true
+    if (mStride == mWidth * 4) {
+        PRUint32 *imgData = (PRUint32*) mImageSurface->Data();
+        PRUint32 firstPixel = * (PRUint32*) imgData;
+        PRUint32 pixelCount = mWidth * mHeight + 1;
 
-            mSinglePixel = PR_TRUE;
+        while (--pixelCount && *imgData++ == firstPixel)
+            ;
 
-            return NS_OK;
+        if (pixelCount == 0) {
+            // all pixels were the same
+            if (mFormat == gfxImageSurface::ImageFormatARGB32 ||
+                mFormat == gfxImageSurface::ImageFormatRGB24)
+            {
+                mSinglePixelColor = gfxRGBA
+                    (firstPixel,
+                     (mFormat == gfxImageSurface::ImageFormatRGB24 ?
+                      gfxRGBA::PACKED_XRGB :
+                      gfxRGBA::PACKED_ARGB_PREMULTIPLIED));
+
+                mSinglePixel = PR_TRUE;
+
+                // XXX we can't do this until we either teach anyone
+                // who calls GetSurface() about single-color stuff,
+                // or until we make GetSurface() create a new temporary
+                // surface to return (and that callers understand that
+                // modifying that surface won't modify the image).
+                // Current users are drag & drop and clipboard.
+#if 0
+                // blow away the older surfaces, to release data
+
+                mImageSurface = nsnull;
+                mOptSurface = nsnull;
+#ifdef XP_WIN
+                mWinSurface = nsnull;
+#endif
+#ifdef XP_MACOSX
+                mQuartzSurface = nsnull;
+#endif
+#endif
+                return NS_OK;
+            }
         }
 
-        // if it's not RGB24/ARGB32, don't optimize, but we should
-        // never hit this.
+        // if it's not RGB24/ARGB32, don't optimize, but we never hit this at the moment
     }
 
     // if we're being forced to use image surfaces due to
-    // resource constraints, don't try to optimize beyond single-pixel.
+    // resource constraints, don't try to optimize beyond same-pixel.
     if (ShouldUseImageSurfaces())
         return NS_OK;