Mac: Optimize HistoryOverlayView using layer.

chrome/browser/ui/cocoa/history_overlay_controller.mm

 // 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.
 
 #import "chrome/browser/ui/cocoa/history_overlay_controller.h"
 
 #include "base/logging.h"
+#include "base/mac/scoped_cftyperef.h"
 #import "chrome/browser/ui/cocoa/browser_window_controller.h"
 #include "grit/theme_resources.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/image/image.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include <cmath>
 
 // Constants ///////////////////////////////////////////////////////////////////
@@ skipping 27 matching lines @@
 @implementation HistoryOverlayView
 
 @synthesize shieldAlpha = shieldAlpha_;
 
 - (id)initWithMode:(HistoryOverlayMode)mode
              image:(NSImage*)image {
   NSRect frame = NSMakeRect(0, 0, kShieldWidth, kShieldHeight);
   if ((self = [super initWithFrame:frame])) {
     mode_ = mode;
 
+    // A layer-hosting view.
+    [self setLayer:[CALayer layer]];
+    [self setWantsLayer:YES];
+
     // If going backward, the arrow needs to be in the right half of the circle,
     // so offset the X position.
     CGFloat offset = mode_ == kHistoryOverlayModeBack ? kShieldRadius : 0;
     NSRect arrowRect = NSMakeRect(offset, 0, kShieldRadius, kShieldHeight);
     arrowRect = NSInsetRect(arrowRect, 10, 0);  // Give a little padding.
 
     base::scoped_nsobject<NSImageView> imageView(
         [[NSImageView alloc] initWithFrame:arrowRect]);
     [imageView setImage:image];
     [imageView setAutoresizingMask:NSViewMinYMargin | NSViewMaxYMargin];
     [self addSubview:imageView];
   }
   return self;
 }
 
-- (void)drawRect:(NSRect)dirtyRect {
-  NSBezierPath* path = [NSBezierPath bezierPathWithOvalInRect:self.bounds];
-  NSColor* fillColor = [NSColor colorWithCalibratedWhite:0 alpha:shieldAlpha_];
-  [fillColor set];
-  [path fill];
+- (void)setFrameSize:(CGSize)frameSize {
+  [super setFrameSize:frameSize];
+  // Draw an oval.
+  CGFloat radius = std::min(frameSize.width, frameSize.height) / 2.0;

[Robert Sesek, 2015/02/04 00:21:13]

Why min here instead of just always width?

[Andre, 2015/02/04 01:08:55]

height >= width always, so that would work.
Done.
Thinking about this some more, setting corner radius this way is not exactly the
same
as drawing an oval as before. But with the width and height being pretty close
in this
case (140x150), it's very hard to tell the difference.
Do you think it's worth trying to use a CAShapeLayer instead?

+  [[self layer] setCornerRadius:radius];
+}
+
+- (void)setShieldAlpha:(CGFloat)shieldAlpha {
+  shieldAlpha_ = shieldAlpha;
+  base::ScopedCFTypeRef<CGColorRef> fillColor(
+      CGColorCreateGenericGray(0, shieldAlpha));
+  [[self layer] setBackgroundColor:fillColor];
 }
 
 @end
 
 // HistoryOverlayController ////////////////////////////////////////////////////
 
 @implementation HistoryOverlayController
 
 - (id)initForMode:(HistoryOverlayMode)mode {
   if ((self = [super init])) {
@@ skipping 37 matching lines @@
   frame.origin.y = (NSHeight(parentFrame) / 2) - (height / 2);
 
   CGFloat width = std::min(kShieldRadius * gestureAmount, kShieldRadius);
   if (mode_ == kHistoryOverlayModeForward)
     frame.origin.x = NSMaxX(parentFrame) - width;
   else if (mode_ == kHistoryOverlayModeBack)
     frame.origin.x = NSMinX(parentFrame) - kShieldWidth + width;
 
   self.view.frame = frame;
   [contentView_ setShieldAlpha:shieldAlpha];
-  [contentView_ setNeedsDisplay:YES];
 }
 
 - (void)showPanelForView:(NSView*)view {
   parent_.reset([view retain]);
   [self setProgress:0 finished:NO];  // Set initial view position.
   [parent_  addSubview:self.view];
 }
 
 - (void)dismiss {
   const CGFloat kFadeOutDurationSeconds = 0.4;
@@ skipping 15 matching lines @@
 }
 
 - (void)animationDidStop:(CAAnimation*)theAnimation finished:(BOOL)finished {
   [self.view removeFromSuperview];
   // Destroy the CAAnimation and its strong reference to its delegate (this
   // class).
   [self.view setAnimations:nil];
 }
 
 @end