Use SkLerpXfermode to blend LabelButton images.

ui/views/controls/button/label_button_border.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/controls/button/label_button_border.h"
 
 #include "base/logging.h"
 #include "grit/ui_resources.h"
+#include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/effects/SkLerpXfermode.h"
 #include "ui/base/animation/animation.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/rect.h"
+#include "ui/gfx/skia_util.h"
 #include "ui/gfx/sys_color_change_listener.h"
 #include "ui/native_theme/native_theme.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/native_theme_delegate.h"
 
 namespace views {
 
 namespace {
 
 // Insets for the unified button images. This assumes that the images
@@ skipping 89 matching lines @@
   const NativeThemeDelegate* native_theme_delegate =
       static_cast<const LabelButton*>(&view);
   ui::NativeTheme::Part part = native_theme_delegate->GetThemePart();
   gfx::Rect rect(native_theme_delegate->GetThemePaintRect());
   ui::NativeTheme::ExtraParams extra;
   const ui::NativeTheme* theme = view.GetNativeTheme();
   const ui::Animation* animation = native_theme_delegate->GetThemeAnimation();
   ui::NativeTheme::State state = native_theme_delegate->GetThemeState(&extra);
 
   if (animation && animation->is_animating()) {
-    // Composite the background and foreground painters during state animations.
-    int alpha = animation->CurrentValueBetween(0, 0xff);
+    // Linearly interpolate background and foreground painters during animation.
+    const SkRect sk_rect = gfx::RectToSkRect(rect);
+    canvas->sk_canvas()->saveLayer(&sk_rect, NULL);
     state = native_theme_delegate->GetBackgroundThemeState(&extra);
-    canvas->SaveLayerAlpha(static_cast<uint8>(0xff - alpha));
     PaintHelper(this, canvas, theme, part, state, rect, extra);
-    canvas->Restore();
 
+    SkPaint paint;
+    skia::RefPtr<SkXfermode> sk_lerp_xfer =
+        skia::AdoptRef(SkLerpXfermode::Create(animation->GetCurrentValue()));
+    paint.setXfermode(sk_lerp_xfer.get());
+    canvas->sk_canvas()->saveLayer(&sk_rect, &paint);
     state = native_theme_delegate->GetForegroundThemeState(&extra);
-    canvas->SaveLayerAlpha(static_cast<uint8>(alpha));
     PaintHelper(this, canvas, theme, part, state, rect, extra);
-    canvas->Restore();
+    canvas->sk_canvas()->restore();
+
+    canvas->sk_canvas()->restore();
   } else {
     PaintHelper(this, canvas, theme, part, state, rect, extra);
   }
 
   // For inverted color schemes, draw a solid fill with the button color.
   if (gfx::IsInvertedColorScheme()) {
     rect.Inset(insets_);
     canvas->FillRect(rect, extra.button.background_color);
   }
 
@@ skipping 12 matching lines @@
   return painters_[focused ? 1 : 0][state].get();
 }
 
 void LabelButtonBorder::SetPainter(bool focused,
                                    Button::ButtonState state,
                                    Painter* painter) {
   painters_[focused ? 1 : 0][state].reset(painter);
 }
 
 }  // namespace views