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/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 {
@@ skipping 93 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.
+    canvas->sk_canvas()->saveLayer(NULL, NULL);

[reed1, 2013/08/14 13:33:56]

Not specific to this CL, but..

Skia definitely takes advantage of the optional rect parameter in saveLayer. If
you pass it, it will limit the size of the offscreen, which saves time both for
initialization and during the restore (when we 'compose' the layer).

Do we have this rect (or a conservative version of it?)

[msw, 2013/08/14 16:17:11]

Done.

     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;
+    paint.setXfermode(SkLerpXfermode::Create(animation->GetCurrentValue()));

[reed1, 2013/08/14 13:33:56]

Create returns an object of reference-count 1
setXfermode will increment that reference-count (to 2)
the paint's destructor will decrement it back to 1 .... LEAK

The fix is to call unref somehow on the xfermode itself.

either

paint.setXfermode(Create(...))->unref()

or

SkAutoTUnref<SkXfermode> mode(Create(...));
paint.setXfermode(mode);

will do the trick

[msw, 2013/08/14 16:17:11]

Done. I too easily forgot how tricky using skia in chrome can be.

+    canvas->sk_canvas()->saveLayer(NULL, &paint);

[reed1, 2013/08/14 13:33:56]

Same comment here about the value of passing in a bounds-rect to saveLayer

[msw, 2013/08/14 16:17:11]

Done.

     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