Windows: Fix opacity of drag images.

BUG=XXX
TEST=Go to google.com, drag logo around. Preview image should now look nice.

Review URL: http://codereview.chromium.org/2963009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@52484 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 54 insertions, 0 deletions

diff --git a/gfx/skbitmap_operations.cc b/gfx/skbitmap_operations.cc
index 27508ba..b8cec11 100644
--- a/gfx/skbitmap_operations.cc
+++ b/gfx/skbitmap_operations.cc
@@ -668,3 +668,30 @@ SkBitmap SkBitmapOperations::DownsampleByTwo(const SkBitmap& bitmap) {
   return result;
 }
 
+// static
+SkBitmap SkBitmapOperations::UnPreMultiply(const SkBitmap& bitmap) {
+  if (bitmap.isNull())
+    return bitmap;
+  if (bitmap.isOpaque())
+    return bitmap;
+
+  SkBitmap opaque_bitmap;
+  opaque_bitmap.setConfig(bitmap.config(), bitmap.width(), bitmap.height());
+  opaque_bitmap.allocPixels();
+
+  {
+    SkAutoLockPixels bitmap_lock(bitmap);
+    SkAutoLockPixels opaque_bitmap_lock(opaque_bitmap);
+    for (int y = 0; y < opaque_bitmap.height(); y++) {
+      for (int x = 0; x < opaque_bitmap.width(); x++) {
+        uint32 src_pixel = *bitmap.getAddr32(x, y);
+        uint32* dst_pixel = opaque_bitmap.getAddr32(x, y);
+        SkColor unmultiplied = SkUnPreMultiply::PMColorToColor(src_pixel);
+        *dst_pixel = unmultiplied;
+      }
+    }
+  }
+
+  opaque_bitmap.setIsOpaque(true);
+  return opaque_bitmap;
+}
diff --git a/gfx/skbitmap_operations.h b/gfx/skbitmap_operations.h
index 1308308..6f808e7 100644
--- a/gfx/skbitmap_operations.h
+++ b/gfx/skbitmap_operations.h
@@ -82,6 +82,12 @@ class SkBitmapOperations {
   // 4 pixels. This is one step in generating a mipmap.
   static SkBitmap DownsampleByTwo(const SkBitmap& bitmap);
 
+  // Unpremultiplies all pixels in |bitmap|. You almost never want to call
+  // this, as |SkBitmap|s are always premultiplied by conversion. Call this
+  // only if you will pass the bitmap's data into a system function that
+  // doesn't expect premultiplied colors.
+  static SkBitmap UnPreMultiply(const SkBitmap& bitmap);
+
  private:
   SkBitmapOperations();  // Class for scoping only.
 
diff --git a/gfx/skbitmap_operations_unittest.cc b/gfx/skbitmap_operations_unittest.cc
index e99f594..83b732a0 100644
--- a/gfx/skbitmap_operations_unittest.cc
+++ b/gfx/skbitmap_operations_unittest.cc
@@ -471,3 +471,24 @@ TEST(SkBitmapOperationsTest, DownsampleByTwoUntilSize) {
   EXPECT_EQ(25, result.width());
   EXPECT_EQ(11, result.height());
 }
+
+TEST(SkBitmapOperationsTest, UnPreMultiply) {
+  SkBitmap input;
+  input.setConfig(SkBitmap::kARGB_8888_Config, 2, 2);
+  input.allocPixels();
+
+  *input.getAddr32(0, 0) = 0x80000000;
+  *input.getAddr32(1, 0) = 0x80808080;
+  *input.getAddr32(0, 1) = 0xFF00CC88;
+  *input.getAddr32(1, 1) = 0x0000CC88;
+
+  SkBitmap result = SkBitmapOperations::UnPreMultiply(input);
+  EXPECT_EQ(2, result.width());
+  EXPECT_EQ(2, result.height());
+
+  SkAutoLockPixels lock(result);
+  EXPECT_EQ(0x80000000, *result.getAddr32(0, 0));
+  EXPECT_EQ(0x80FFFFFF, *result.getAddr32(1, 0));
+  EXPECT_EQ(0xFF00CC88, *result.getAddr32(0, 1));
+  EXPECT_EQ(0x00000000u, *result.getAddr32(1, 1));  // "Division by zero".
+}