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 415 matching lines @@
 
     switch (_featureToAnimate) {
     case ThumbAlpha:
         [_scrollbarPainter.get() setKnobAlpha:currentValue];
         break;
     case TrackAlpha:
         [_scrollbarPainter.get() setTrackAlpha:currentValue];
         break;
     case UIStateTransition:
         [_scrollbarPainter.get() setUiStateTransitionProgress:currentValue];
+        _scrollbar->setThumbNeedsRepaint(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
 {
+    enum {
+        NSScrollerStateInvisible = 0,

[chrishtr, 2015/11/24 21:15:12]

Forgive my ignorance of Objective C. When is NSScrollerStateInvisible ever set?

[ccameron, 2015/11/25 00:23:01]

That is a value of the newOverlayScrollerState parameter.

This (and the rest of the file) are undocumented private APIs that come from
WebKit (checked in back when this was common with Safari). The enum values of
newOverlayScrollerState are not documented -- I've found empirically that this
is called with the listed 3 states, and so I've added labels for them here.

+        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 137 matching lines @@
 void ScrollAnimatorMac::mouseMovedInContentArea() const
 {
     if (!scrollableArea()->scrollbarsCanBeActive())
         return;
     if (ScrollbarThemeMacCommon::isOverlayAPIAvailable())
         [m_scrollbarPainterController.get() mouseMovedInContentArea];
 }
 
 void ScrollAnimatorMac::mouseEnteredScrollbar(Scrollbar* scrollbar) const
 {
-    // At this time, only legacy scrollbars needs to send notifications here.
-    if (ScrollbarThemeMacCommon::recommendedScrollerStyle() != NSScrollerStyleLegacy)

[chrishtr, 2015/11/24 21:15:12]

What do the changes here and on line 819 do?

[ccameron, 2015/11/25 00:23:02]

I set the wrong upstream branch -- this is part of another commit (it's gone
now).

For reference, the comment comes in from a WebKit commit in 2012
(https://bugs.webkit.org/show_bug.cgi?id=76133), and is not true on 10.9+.
Again, no documentation, behavior changing between OS releases.

-        return;
-
     if (!scrollableArea()->scrollbarsCanBeActive())
         return;
 
     if (ScrollbarThemeMacCommon::isOverlayAPIAvailable()) {
         if (!supportsUIStateTransitionProgress())
             return;
         if (ScrollbarPainter painter = scrollbarPainterForScrollbar(scrollbar))
             [painter mouseEnteredScroller];
     }
 }
 
 void ScrollAnimatorMac::mouseExitedScrollbar(Scrollbar* scrollbar) const
 {
-    // At this time, only legacy scrollbars needs to send notifications here.
-    if (ScrollbarThemeMacCommon::recommendedScrollerStyle() != NSScrollerStyleLegacy)
-        return;
-
     if (!scrollableArea()->scrollbarsCanBeActive())
         return;
 
     if (ScrollbarThemeMacCommon::isOverlayAPIAvailable()) {
         if (!supportsUIStateTransitionProgress())
             return;
         if (ScrollbarPainter painter = scrollbarPainterForScrollbar(scrollbar))
             [painter mouseExitedScroller];
     }
 }
@@ skipping 237 matching lines @@
 
     ScrollbarThemeMacOverlayAPI* macTheme = macOverlayScrollbarTheme();
     if (!macTheme) {
         m_needsScrollerStyleUpdate = false;
         return;
     }
 
     NSScrollerStyle newStyle = [m_scrollbarPainterController.get() scrollerStyle];
 
     if (Scrollbar* verticalScrollbar = scrollableArea()->verticalScrollbar()) {
+        verticalScrollbar->setTrackBackgroundNeedsRepaint(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->setTrackBackgroundNeedsRepaint(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