2 files changed, 62 insertions, 0 deletions
diff --git a/skia/ext/image_operations.cc b/skia/ext/image_operations.cc
index 561bd4e..c0ee3e0 100644
--- a/skia/ext/image_operations.cc
+++ b/skia/ext/image_operations.cc
@@ -407,6 +407,59 @@ SkBitmap ImageOperations::CreateMaskedBitmap(const SkBitmap& rgb,
   return masked;
 }
 
+// static
+SkBitmap ImageOperations::CreateButtonBackground(SkColor color,
+                                                 const SkBitmap& image,
+                                                 const SkBitmap& mask) {
+  DCHECK(image.config() == SkBitmap::kARGB_8888_Config);
+  DCHECK(mask.config() == SkBitmap::kARGB_8888_Config);
+
+  SkBitmap background;
+  background.setConfig(SkBitmap::kARGB_8888_Config,
+                       mask.width(),
+                       mask.height(), 0);
+  background.allocPixels();
+
+  int bg_a = SkColorGetA(color);
+  int bg_r = SkColorGetR(color);
+  int bg_g = SkColorGetG(color);
+  int bg_b = SkColorGetB(color);
+
+  SkAutoLockPixels lock_mask(mask);
+  SkAutoLockPixels lock_image(image);
+  SkAutoLockPixels lock_background(background);
+
+  for (int y = 0; y < mask.height(); y++) {
+    uint32* dst_row = background.getAddr32(0, y);
+    uint32* image_row = image.getAddr32(0, y % image.height());
+    uint32* mask_row = mask.getAddr32(0, y);
+
+    for (int x = 0; x < mask.width(); x++) {
+      uint32 mask_pixel = mask_row[x];
+      uint32 image_pixel = image_row[x % image.width()];
+
+      int img_a = SkColorGetA(image_pixel);
+      int img_r = SkColorGetR(image_pixel);
+      int img_g = SkColorGetG(image_pixel);
+      int img_b = SkColorGetB(image_pixel);
+
+      double img_alpha = static_cast<double>(img_a) / 255.0;
+      double img_inv = 1 - img_alpha;
+
+      double mask_a = static_cast<double>(SkColorGetA(mask_pixel)) / 255.0;
+
+      dst_row[x] = SkColorSetARGB(
+          static_cast<int>(std::min(255, bg_a + img_a) * mask_a),
+          static_cast<int>((bg_r * img_inv + img_r * img_alpha) * mask_a),
+          static_cast<int>((bg_g * img_inv + img_g * img_alpha) * mask_a),
+          static_cast<int>((bg_b * img_inv + img_b * img_alpha) * mask_a));
+    }
+  }
+
+  return background;
+}
+
+
 SkBitmap ImageOperations::CreateBlurredBitmap(const SkBitmap& bitmap,
                                               int blur_amount ) {
   DCHECK(bitmap.config() == SkBitmap::kARGB_8888_Config);
diff --git a/skia/ext/image_operations.h b/skia/ext/image_operations.h
index 3086fab..4e3c93e 100644
--- a/skia/ext/image_operations.h
+++ b/skia/ext/image_operations.h
@@ -61,6 +61,15 @@ class ImageOperations {
   static SkBitmap CreateMaskedBitmap(const SkBitmap& first,
                                      const SkBitmap& alpha);
 
+  // We create a button background image by compositing the color and image 
+  // together, then applying the mask. This is a highly specialized composite 
+  // operation that is the equivalent of drawing a background in |color|, 
+  // tiling |image| over the top, and then masking the result out with |mask|.
+  // The images must use kARGB_8888_Config config.
+  static SkBitmap CreateButtonBackground(SkColor color,
+                                         const SkBitmap& image,
+                                         const SkBitmap& mask);
+
   // Blur a bitmap using an average-blur algorithm over the rectangle defined
   // by |blur_amount|. The blur will wrap around image edges.
   static SkBitmap CreateBlurredBitmap(const SkBitmap& bitmap, int blur_amount);