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

4 files changed, 65 insertions, 16 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".
+}
diff --git a/views/drag_utils_win.cc b/views/drag_utils_win.cc
index 84b4ba1..d21d37f 100644
--- a/views/drag_utils_win.cc
+++ b/views/drag_utils_win.cc
@@ -12,6 +12,7 @@
 #include "app/os_exchange_data_provider_win.h"
 #include "gfx/canvas_skia.h"
 #include "gfx/gdi_util.h"
+#include "gfx/skbitmap_operations.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 namespace drag_utils {
@@ -35,23 +36,18 @@ static void SetDragImageOnDataObject(HBITMAP hbitmap,
 
 // Blit the contents of the canvas to a new HBITMAP. It is the caller's
 // responsibility to release the |bits| buffer.
-static HBITMAP CreateBitmapFromCanvas(const gfx::CanvasSkia& canvas,
-                                      int width,
-                                      int height) {
+static HBITMAP CreateHBITMAPFromSkBitmap(const SkBitmap& sk_bitmap) {
   HDC screen_dc = GetDC(NULL);
   BITMAPINFOHEADER header;
-  gfx::CreateBitmapHeader(width, height, &header);
+  gfx::CreateBitmapHeader(sk_bitmap.width(), sk_bitmap.height(), &header);
   void* bits;
   HBITMAP bitmap =
       CreateDIBSection(screen_dc, reinterpret_cast<BITMAPINFO*>(&header),
                        DIB_RGB_COLORS, &bits, NULL, 0);
-  HDC compatible_dc = CreateCompatibleDC(screen_dc);
-  HGDIOBJ old_object = SelectObject(compatible_dc, bitmap);
-  BitBlt(compatible_dc, 0, 0, width, height,
-         canvas.getTopPlatformDevice().getBitmapDC(),
-         0, 0, SRCCOPY);
-  SelectObject(compatible_dc, old_object);
-  ReleaseDC(NULL, compatible_dc);
+  DCHECK(sk_bitmap.rowBytes() == sk_bitmap.width() * 4);
+  SkAutoLockPixels lock(sk_bitmap);
+  memcpy(
+      bits, sk_bitmap.getPixels(), sk_bitmap.height() * sk_bitmap.rowBytes());
   ReleaseDC(NULL, screen_dc);
   return bitmap;
 }
@@ -60,13 +56,12 @@ void SetDragImageOnDataObject(const SkBitmap& sk_bitmap,
                               const gfx::Size& size,
                               const gfx::Point& cursor_offset,
                               OSExchangeData* data_object) {
-  gfx::CanvasSkia canvas(sk_bitmap.width(), sk_bitmap.height(),
-                         /*is_opaque=*/false);
-  canvas.DrawBitmapInt(sk_bitmap, 0, 0);
-
   DCHECK(data_object && !size.IsEmpty());
+  // InitializeFromBitmap() doesn't expect an alpha channel and is confused
+  // by premultiplied colors, so unpremultiply the bitmap.
   // SetDragImageOnDataObject(HBITMAP) takes ownership of the bitmap.
-  HBITMAP bitmap = CreateBitmapFromCanvas(canvas, size.width(), size.height());
+  HBITMAP bitmap = CreateHBITMAPFromSkBitmap(
+      SkBitmapOperations::UnPreMultiply(sk_bitmap));
 
   // Attach 'bitmap' to the data_object.
   SetDragImageOnDataObject(bitmap, size, cursor_offset,