Mac: Don't repaint scrollbars every frame

third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 20 matching lines @@
 #include "platform/graphics/paint/DisplayItem.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "public/platform/mac/MacScrollTypes.h"
 
 namespace blink {
 
 class CullRect;
 class GraphicsContext;
 class PlatformMouseEvent;
 class ScrollbarThemeClient;
+class ScrollbarThemePaintParams;
 
 class PLATFORM_EXPORT ScrollbarTheme {
     WTF_MAKE_NONCOPYABLE(ScrollbarTheme); USING_FAST_MALLOC(ScrollbarTheme);
 public:
     ScrollbarTheme() { }
     virtual ~ScrollbarTheme() { }
 
+    // If true, then scrollbars with this theme will be painted every time
+    // Scrollbar::setNeedsPaintInvalidation is called. If false, then scrollbar
+    // thumb and track part painting results will be cached and not repainted
+    // unless requested by Scrollbar::setNeedsPaintThumb or
+    // Scrollbar::setNeedsPaintTrack.
+    virtual bool shouldRepaintAllPartsOnInvalidation() const { return true; }
+
     virtual void updateEnabledState(const ScrollbarThemeClient*) { }
 
     virtual bool paint(const ScrollbarThemeClient*, GraphicsContext*, const CullRect&);
 
     virtual ScrollbarPart hitTest(const ScrollbarThemeClient*, const IntPoint&);
 
     virtual int scrollbarThickness(ScrollbarControlSize = RegularScrollbar) { return 0; }
     virtual int scrollbarMargin() const { return 0; }
 
     virtual ScrollbarButtonsPlacement buttonsPlacement() const { return ScrollbarButtonsPlacementSingle; }
@@ skipping 12 matching lines @@
     virtual bool shouldDragDocumentInsteadOfThumb(const ScrollbarThemeClient*, const PlatformMouseEvent&) { return false; }
 
     // The position of the thumb relative to the track.
     virtual int thumbPosition(const ScrollbarThemeClient*);
     // The length of the thumb along the axis of the scrollbar.
     virtual int thumbLength(const ScrollbarThemeClient*);
     // The position of the track relative to the scrollbar.
     virtual int trackPosition(const ScrollbarThemeClient*);
     // The length of the track along the axis of the scrollbar.
     virtual int trackLength(const ScrollbarThemeClient*);
+    // The opacity of the thumb (only non-opaque for Mac overlay scrollbars).

[chrishtr, 2015/11/23 18:59:42]

Don't specify Mac-specific semantics.

[ccameron, 2015/11/24 01:12:05]

Removed (I'd prefer to say specify the use, at least with an "e.g" if not an
"only", though).

+    virtual float thumbOpacity(const ScrollbarThemeClient*) const { return 1.0f; }

[chrishtr, 2015/11/23 18:59:42]

How is the client supposed to know whether the opacity is included in the
SkPicture painted by the scrollbar, or it's ok to animate it separately?

[ccameron, 2015/11/24 01:12:05]

Opacity is always taken into account when re-drawing (it has no cost to change,
unlike re-painting the SkPicture).

[chrishtr, 2015/11/24 19:02:07]

What I mean is: what is the correct way to interpret this API from the cc
perspective? If opacity is < 1 then always apply it as an effect on top of the
SkPicture, and if opacity == 1 don't? And this works for non-Mac because there
is no transparency for the other themes right now?

+    // The opacity of the track (only non-opaque for Mac overlay scrollbars).
+    virtual float trackOpacity(const ScrollbarThemeClient*) const { return 1.0f; }
 
     virtual bool hasButtons(const ScrollbarThemeClient*) = 0;
     virtual bool hasThumb(const ScrollbarThemeClient*) = 0;
 
     virtual IntRect backButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) = 0;
     virtual IntRect forwardButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) = 0;
     virtual IntRect trackRect(const ScrollbarThemeClient*, bool painting = false) = 0;
     virtual IntRect thumbRect(const ScrollbarThemeClient*);
     virtual int thumbThickness(const ScrollbarThemeClient*);
 
@@ skipping 28 matching lines @@
     static DisplayItem::Type buttonPartToDisplayItemType(ScrollbarPart);
     static DisplayItem::Type trackPiecePartToDisplayItemType(ScrollbarPart);
 
 private:
     static ScrollbarTheme* nativeTheme(); // Must be implemented to return the correct theme subclass.
     static bool gMockScrollbarsEnabled;
 };
 
 }
 #endif