Mac: Don't repaint scrollbars every frame

third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 2011 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 412 matching lines @@
         currentValue = 1 - progress;
     else
         currentValue = progress;
 
     switch (_featureToAnimate) {
     case ThumbAlpha:
         [_scrollbarPainter.get() setKnobAlpha:currentValue];
         break;
     case TrackAlpha:
         [_scrollbarPainter.get() setTrackAlpha:currentValue];
+        _scrollbar->setTrackNeedsRepaint(true);
         break;
     case UIStateTransition:
         [_scrollbarPainter.get() setUiStateTransitionProgress:currentValue];
+        _scrollbar->setThumbNeedsRepaint(true);
+        _scrollbar->setTrackNeedsRepaint(true);
         break;
     case ExpansionTransition:
         [_scrollbarPainter.get() setExpansionTransitionProgress:currentValue];
+        _scrollbar->setThumbNeedsRepaint(true);
         break;
     }
 
     _scrollbar->setNeedsPaintInvalidation();
 }
 
 - (void)invalidate
 {
     BEGIN_BLOCK_OBJC_EXCEPTIONS;
     [self stopAnimation];
     END_BLOCK_OBJC_EXCEPTIONS;
     _scrollbar = 0;
 }
 
 @end
 
 @interface WebScrollbarPainterDelegate : NSObject<NSAnimationDelegate>
 {
     blink::Scrollbar* _scrollbar;
 
     RetainPtr<WebScrollbarPartAnimation> _knobAlphaAnimation;
     RetainPtr<WebScrollbarPartAnimation> _trackAlphaAnimation;
     RetainPtr<WebScrollbarPartAnimation> _uiStateTransitionAnimation;
     RetainPtr<WebScrollbarPartAnimation> _expansionTransitionAnimation;
+    BOOL _hasExpandedSinceInvisible;
 }
 - (id)initWithScrollbar:(blink::Scrollbar*)scrollbar;
 - (void)updateVisibilityImmediately:(bool)show;
 - (void)cancelAnimations;
 @end
 
 @implementation WebScrollbarPainterDelegate
 
 - (id)initWithScrollbar:(blink::Scrollbar*)scrollbar
 {
@@ skipping 162 matching lines @@
         // If we don't need to initialize the animation, just reset the values in case they have changed.
         [_expansionTransitionAnimation.get() setStartValue:[scrollbarPainter uiStateTransitionProgress]];
         [_expansionTransitionAnimation.get() setEndValue:1.0];
         [_expansionTransitionAnimation.get() setDuration:duration];
     }
     [_expansionTransitionAnimation.get() startAnimation];
 }
 
 - (void)scrollerImp:(id)scrollerImp overlayScrollerStateChangedTo:(NSUInteger)newOverlayScrollerState
 {
+    // The names of these states are based on their observed behavior, and are not based on documentation.
+    enum {
+        NSScrollerStateInvisible = 0,
+        NSScrollerStateKnob = 1,
+        NSScrollerStateExpanded = 2
+    };
+    // We do not receive notifications about the thumb un-expanding when the scrollbar fades away. Ensure
+    // that we re-paint the thumb the next time that we transition away from being invisible, so that
+    // the thumb doesn't stick in an expanded state.
+    if (newOverlayScrollerState == NSScrollerStateExpanded) {
+        _hasExpandedSinceInvisible = YES;
+    } else if (newOverlayScrollerState != NSScrollerStateInvisible && _hasExpandedSinceInvisible) {
+        _scrollbar->setThumbNeedsRepaint(true);
+        _hasExpandedSinceInvisible = NO;
+    }
 }
 
 - (void)invalidate
 {
     _scrollbar = 0;
     BEGIN_BLOCK_OBJC_EXCEPTIONS;
     [_knobAlphaAnimation.get() invalidate];
     [_trackAlphaAnimation.get() invalidate];
     [_uiStateTransitionAnimation.get() invalidate];
     [_expansionTransitionAnimation.get() invalidate];
@@ skipping 407 matching lines @@
 
     ScrollbarThemeMacOverlayAPI* macTheme = macOverlayScrollbarTheme();
     if (!macTheme) {
         m_needsScrollerStyleUpdate = false;
         return;
     }
 
     NSScrollerStyle newStyle = [m_scrollbarPainterController.get() scrollerStyle];
 
     if (Scrollbar* verticalScrollbar = scrollableArea()->verticalScrollbar()) {
+        verticalScrollbar->setTrackNeedsRepaint(true);
+        verticalScrollbar->setThumbNeedsRepaint(true);
         verticalScrollbar->setNeedsPaintInvalidation();
 
         ScrollbarPainter oldVerticalPainter = [m_scrollbarPainterController.get() verticalScrollerImp];
         ScrollbarPainter newVerticalPainter = [NSClassFromString(@"NSScrollerImp") scrollerImpWithStyle:newStyle
                                                                                     controlSize:(NSControlSize)verticalScrollbar->controlSize()
                                                                                     horizontal:NO
                                                                                     replacingScrollerImp:oldVerticalPainter];
         [m_scrollbarPainterController.get() setVerticalScrollerImp:newVerticalPainter];
         macTheme->setNewPainterForScrollbar(verticalScrollbar, newVerticalPainter);
 
         // The different scrollbar styles have different thicknesses, so we must re-set the
         // frameRect to the new thickness, and the re-layout below will ensure the position
         // and length are properly updated.
         int thickness = macTheme->scrollbarThickness(verticalScrollbar->controlSize());
         verticalScrollbar->setFrameRect(IntRect(0, 0, thickness, thickness));
     }
 
     if (Scrollbar* horizontalScrollbar = scrollableArea()->horizontalScrollbar()) {
+        horizontalScrollbar->setTrackNeedsRepaint(true);
+        horizontalScrollbar->setThumbNeedsRepaint(true);
         horizontalScrollbar->setNeedsPaintInvalidation();
 
         ScrollbarPainter oldHorizontalPainter = [m_scrollbarPainterController.get() horizontalScrollerImp];
         ScrollbarPainter newHorizontalPainter = [NSClassFromString(@"NSScrollerImp") scrollerImpWithStyle:newStyle
                                                                                     controlSize:(NSControlSize)horizontalScrollbar->controlSize()
                                                                                     horizontal:YES
                                                                                     replacingScrollerImp:oldHorizontalPainter];
         [m_scrollbarPainterController.get() setHorizontalScrollerImp:newHorizontalPainter];
         macTheme->setNewPainterForScrollbar(horizontalScrollbar, newHorizontalPainter);
 
@@ skipping 64 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return ScrollbarThemeMacCommon::isOverlayAPIAvailable();
 }
 
 } // namespace blink