Mac: Optimize TabView drawing.

chrome/browser/ui/cocoa/tabs/tab_view.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/tabs/tab_view.h"
 
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "base/strings/sys_string_conversions.h"
 #include "chrome/browser/themes/theme_service.h"
 #import "chrome/browser/ui/cocoa/tabs/media_indicator_button_cocoa.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_window_controller.h"
 #import "chrome/browser/ui/cocoa/themed_window.h"
 #import "chrome/browser/ui/cocoa/view_id_util.h"
 #include "chrome/grit/generated_resources.h"
 #include "grit/theme_resources.h"
 #import "third_party/google_toolbox_for_mac/src/AppKit/GTMFadeTruncatingTextFieldCell.h"
 #import "ui/base/cocoa/nsgraphics_context_additions.h"
 #import "ui/base/cocoa/nsview_additions.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 
 
-const int kMaskHeight = 29;  // Height of the mask bitmap.
 const int kFillHeight = 25;  // Height of the "mask on" part of the mask bitmap.
 
 // The amount of time in seconds during which each type of glow increases, holds
 // steady, and decreases, respectively.
 const NSTimeInterval kHoverShowDuration = 0.2;
 const NSTimeInterval kHoverHoldDuration = 0.02;
 const NSTimeInterval kHoverHideDuration = 0.4;
 const NSTimeInterval kAlertShowDuration = 0.4;
 const NSTimeInterval kAlertHoldDuration = 0.4;
 const NSTimeInterval kAlertHideDuration = 0.4;
 
 // The default time interval in seconds between glow updates (when
 // increasing/decreasing).
 const NSTimeInterval kGlowUpdateInterval = 0.025;
 
 // This is used to judge whether the mouse has moved during rapid closure; if it
 // has moved less than the threshold, we want to close the tab.
 const CGFloat kRapidCloseDist = 2.5;
 
+namespace {
+
+// A wrapper around NSDrawThreePartImage that caches the images.
+// The middle image is optional.
+class ThreePartImage {
+ public:
+  ThreePartImage(int left_id, int middle_id, int right_id) {
+    DCHECK(left_id);
+    DCHECK(right_id);
+    ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
+    leftImage_.reset(rb.GetNativeImageNamed(left_id).CopyNSImage());
+    rightImage_.reset(rb.GetNativeImageNamed(right_id).CopyNSImage());
+    leftSize_ = [leftImage_ size];
+    rightSize_ = [rightImage_ size];
+
+    if (middle_id)
+      middleImage_.reset(rb.GetNativeImageNamed(middle_id).CopyNSImage());
+  }
+
+  void DrawInRect(NSRect rect, NSCompositingOperation op, CGFloat alpha) {
+    rect.size.height = leftSize_.height;
+    NSDrawThreePartImage(rect, leftImage_, middleImage_, rightImage_,
+                         NO, op, alpha, NO);
+  }
+
+  NSRect GetLeftRect(NSRect bounds) {
+    NSRect left, right;
+    NSDivideRect(bounds, &left, &right, leftSize_.width, NSMinXEdge);
+    return left;
+  }
+
+  NSRect GetMiddleRect(NSRect bounds) {
+    NSRect left, middle, right;
+    NSDivideRect(bounds, &left, &middle, leftSize_.width, NSMinXEdge);
+    NSDivideRect(middle, &right, &middle, rightSize_.width, NSMaxXEdge);
+    return middle;
+  }
+
+  NSRect GetRightRect(NSRect bounds) {
+    NSRect left, right;
+    NSDivideRect(bounds, &right, &left, rightSize_.width, NSMaxXEdge);
+    return right;
+  }
+
+  // Returns YES if |point| is in a non-transparent part of the images.
+  BOOL HitTest(NSPoint point, NSRect bounds) {
+    NSRect middleRect = GetMiddleRect(bounds);
+    if (NSPointInRect(point, middleRect))
+      return middleImage_ ? HitTestImage(point, middleImage_, middleRect) : YES;
+
+    NSRect leftRect = GetLeftRect(bounds);
+    if (NSPointInRect(point, leftRect))
+      return HitTestImage(point, leftImage_, leftRect);
+
+    NSRect rightRect = GetRightRect(bounds);
+    if (NSPointInRect(point, rightRect))
+      return HitTestImage(point, rightImage_, rightRect);
+
+    return NO;
+  }
+
+ private:
+  // Returns YES if |point| is in a non-transparent part of |image|.
+  BOOL HitTestImage(NSPoint point, NSImage* image, NSRect imageRect) {
+    NSRect pointRect = NSMakeRect(point.x, point.y, 1, 1);
+    return [image hitTestRect:pointRect
+        withImageDestinationRect:imageRect
+                         context:nil
+                           hints:nil
+                         flipped:NO];
+  }
+
+  base::scoped_nsobject<NSImage> leftImage_;
+  base::scoped_nsobject<NSImage> middleImage_;
+  base::scoped_nsobject<NSImage> rightImage_;
+  NSSize leftSize_;
+  NSSize rightSize_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreePartImage);
+};
+
+ThreePartImage* GetMaskImage() {
+  static ThreePartImage* mask =
+      new ThreePartImage(IDR_TAB_ALPHA_LEFT, 0, IDR_TAB_ALPHA_RIGHT);
+  return mask;
+}
+
+ThreePartImage* GetStrokeImage(bool active) {
+  static ThreePartImage* activeStroke = new ThreePartImage(
+      IDR_TAB_ACTIVE_LEFT, IDR_TAB_ACTIVE_CENTER, IDR_TAB_ACTIVE_RIGHT);
+  static ThreePartImage* inactiveStroke = new ThreePartImage(
+      IDR_TAB_INACTIVE_LEFT, IDR_TAB_INACTIVE_CENTER, IDR_TAB_INACTIVE_RIGHT);
+
+  return active ? activeStroke : inactiveStroke;
+}
+
+}  // namespace
+
 @interface TabView(Private)
 
 - (void)resetLastGlowUpdateTime;
 - (NSTimeInterval)timeElapsedSinceLastGlowUpdate;
 - (void)adjustGlowValue;
-- (CGImageRef)tabClippingMask;
 
 @end  // TabView(Private)
 
 @implementation TabView
 
 @synthesize state = state_;
 @synthesize hoverAlpha = hoverAlpha_;
 @synthesize alertAlpha = alertAlpha_;
 @synthesize closing = closing_;
 
@@ skipping 12 matching lines @@
     [titleView_ setAutoresizingMask:NSViewWidthSizable];
     base::scoped_nsobject<GTMFadeTruncatingTextFieldCell> labelCell(
         [[GTMFadeTruncatingTextFieldCell alloc] initTextCell:@"Label"]);
     [labelCell setControlSize:NSSmallControlSize];
     CGFloat fontSize = [NSFont systemFontSizeForControlSize:NSSmallControlSize];
     NSFont* font = [NSFont fontWithName:[[labelCell font] fontName]
                                    size:fontSize];
     [labelCell setFont:font];
     [titleView_ setCell:labelCell];
     titleViewCell_ = labelCell;
+
+    [self setWantsLayer:YES];  // -drawFill: needs a layer.
   }
   return self;
 }
 
 - (void)dealloc {
   // Cancel any delayed requests that may still be pending (drags or hover).
   [NSObject cancelPreviousPerformRequestsWithTarget:self];
   [super dealloc];
 }
 
@@ skipping 55 matching lines @@
 }
 
 // Determines which view a click in our frame actually hit. It's either this
 // view or one of the child buttons.
 - (NSView*)hitTest:(NSPoint)aPoint {
   NSView* const defaultHitTestResult = [super hitTest:aPoint];
   if ([defaultHitTestResult isKindOfClass:[NSButton class]])
     return defaultHitTestResult;
 
   NSPoint viewPoint = [self convertPoint:aPoint fromView:[self superview]];
-  NSRect pointRect = NSMakeRect(viewPoint.x, viewPoint.y, 1, 1);
-
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  NSImage* left = rb.GetNativeImageNamed(IDR_TAB_ALPHA_LEFT).ToNSImage();
-  if (viewPoint.x < [left size].width) {
-    NSRect imageRect = NSMakeRect(0, 0, [left size].width, [left size].height);
-    if ([left hitTestRect:pointRect withImageDestinationRect:imageRect
-          context:nil hints:nil flipped:NO]) {
-      return self;
-    }
-    return nil;
-  }
-
-  NSImage* right = rb.GetNativeImageNamed(IDR_TAB_ALPHA_RIGHT).ToNSImage();
-  CGFloat rightX = NSWidth([self bounds]) - [right size].width;
-  if (viewPoint.x > rightX) {
-    NSRect imageRect = NSMakeRect(
-        rightX, 0, [right size].width, [right size].height);
-    if ([right hitTestRect:pointRect withImageDestinationRect:imageRect
-          context:nil hints:nil flipped:NO]) {
-      return self;
-    }
-    return nil;
-  }
-
-  if (viewPoint.y < kFillHeight)
-    return self;
-  return nil;
+  NSRect maskRect = [self bounds];
+  maskRect.size.height = kFillHeight;
+  return GetMaskImage()->HitTest(viewPoint, maskRect) ? self : nil;
 }
 
 // Returns |YES| if this tab can be torn away into a new window.
 - (BOOL)canBeDragged {
   return [controller_ tabCanBeDragged:controller_];
 }
 
 // Handle clicks and drags in this button. We get here because we have
 // overridden acceptsFirstMouse: and the click is within our bounds.
 - (void)mouseDown:(NSEvent*)theEvent {
@@ skipping 107 matching lines @@
     },
   };
 
   // Themes don't have an inactive image so only look for one if there's no
   // theme.
   bool active =
       [[self window] isMainWindow] || !themeProvider->UsingDefaultTheme();
   return themeProvider->GetNSImageColorNamed(bitmapResources[active][selected]);
 }
 
-// Draws the active tab background.
-- (void)drawFillForActiveTab:(NSRect)dirtyRect {
-  NSColor* backgroundImageColor = [self backgroundColorForSelected:YES];
-  [backgroundImageColor set];
-
-  // Themes can have partially transparent images. NSRectFill() is measurably
-  // faster though, so call it for the known-safe default theme.
-  ThemeService* themeProvider =
-      static_cast<ThemeService*>([[self window] themeProvider]);
-  if (themeProvider && themeProvider->UsingDefaultTheme())
-    NSRectFill(dirtyRect);
-  else
-    NSRectFillUsingOperation(dirtyRect, NSCompositeSourceOver);
-}
-
 // Draws the tab background.
 - (void)drawFill:(NSRect)dirtyRect {
   gfx::ScopedNSGraphicsContextSaveGState scopedGState;
+  NSRect bounds = [self bounds];
+
+  NSRect clippingRect = bounds;
+  clippingRect.size.height = kFillHeight;
+  if (state_ != NSOnState) {
+    // Background tabs should not paint over the tab strip separator, which is
+    // two pixels high in both lodpi and hidpi.
+    clippingRect.origin.y = 2 * [self cr_lineWidth];
+    clippingRect.size.height -= clippingRect.origin.y;
+  }
+  NSRectClip(clippingRect);
+
+  NSPoint position = [[self window]
+      themeImagePositionForAlignment:THEME_IMAGE_ALIGN_WITH_TAB_STRIP];
+  [[NSGraphicsContext currentContext] cr_setPatternPhase:position forView:self];
+
+  [[self backgroundColorForSelected:(state_ != NSOffState)] set];
+  NSRectFill(dirtyRect);
+
+  if (state_ == NSOffState)
+    [self drawGlow:dirtyRect];
+
+  // If we filled outside the middle rect, we need to erase what we filled
+  // outside the tab's shape.
+  // This only works if we are drawing to our own backing layer.
+  if (!NSContainsRect(GetMaskImage()->GetMiddleRect(bounds), dirtyRect)) {
+    DCHECK([self layer]);
+    GetMaskImage()->DrawInRect(bounds, NSCompositeDestinationIn, 1.0);
+  }
+}
+
+// Draw the glow for hover and the overlay for alerts.
+- (void)drawGlow:(NSRect)dirtyRect {
   NSGraphicsContext* context = [NSGraphicsContext currentContext];
   CGContextRef cgContext = static_cast<CGContextRef>([context graphicsPort]);
 
-  ThemeService* themeProvider =
-      static_cast<ThemeService*>([[self window] themeProvider]);
-  NSPoint position = [[self window]
-      themeImagePositionForAlignment: THEME_IMAGE_ALIGN_WITH_TAB_STRIP];
-  [context cr_setPatternPhase:position forView:self];
-
-  CGImageRef mask([self tabClippingMask]);
-  CGRect maskBounds = CGRectMake(0, 0, maskCacheWidth_, kMaskHeight);
-  CGContextClipToMask(cgContext, maskBounds, mask);
-
-  // There is only 1 active tab at a time.
-  // It has a different fill color which draws over the separator line.
-  if (state_ == NSOnState) {
-    [self drawFillForActiveTab:dirtyRect];
-    return;
-  }
-
-  // Background tabs should not paint over the tab strip separator, which is
-  // two pixels high in both lodpi and hidpi.
-  if (dirtyRect.origin.y < 1)
-    dirtyRect.origin.y = 2 * [self cr_lineWidth];
-
-  // There can be multiple selected tabs.
-  // They have the same fill color as the active tab, but do not draw over
-  // the separator.
-  if (state_ == NSMixedState) {
-    [self drawFillForActiveTab:dirtyRect];
-    return;
-  }
-
-  // Draw the tab background.
-  NSColor* backgroundImageColor = [self backgroundColorForSelected:NO];
-  [backgroundImageColor set];
-
-  // Themes can have partially transparent images. NSRectFill() is measurably
-  // faster though, so call it for the known-safe default theme.
-  bool usingDefaultTheme = themeProvider && themeProvider->UsingDefaultTheme();
-  if (usingDefaultTheme)
-    NSRectFill(dirtyRect);
-  else
-    NSRectFillUsingOperation(dirtyRect, NSCompositeSourceOver);
-
-  // Draw the glow for hover and the overlay for alerts.
   CGFloat hoverAlpha = [self hoverAlpha];
   CGFloat alertAlpha = [self alertAlpha];
   if (hoverAlpha > 0 || alertAlpha > 0) {
-    gfx::ScopedNSGraphicsContextSaveGState contextSave;

[Robert Sesek, 2015/02/12 17:16:47]

Why remove this line?

[Andre, 2015/02/12 17:23:01]

It seems unnecessary.
The documentation for CGContextBeginTransparencyLayer says that the global alpha
is restored
when the transparency layer is ended.

     CGContextBeginTransparencyLayer(cgContext, 0);
 
     // The alert glow overlay is like the selected state but at most at most 80%
     // opaque. The hover glow brings up the overlay's opacity at most 50%.
     CGFloat backgroundAlpha = 0.8 * alertAlpha;
     backgroundAlpha += (1 - backgroundAlpha) * 0.5 * hoverAlpha;
     CGContextSetAlpha(cgContext, backgroundAlpha);
 
-    [self drawFillForActiveTab:dirtyRect];
+    [[self backgroundColorForSelected:YES] set];
+    NSRectFill(dirtyRect);
 
     // ui::ThemeProvider::HasCustomImage is true only if the theme provides the
     // image. However, even if the theme doesn't provide a tab background, the
     // theme machinery will make one if given a frame image. See
     // BrowserThemePack::GenerateTabBackgroundImages for details.
+    ui::ThemeProvider* themeProvider = [[self window] themeProvider];
     BOOL hasCustomTheme = themeProvider &&
         (themeProvider->HasCustomImage(IDR_THEME_TAB_BACKGROUND) ||
          themeProvider->HasCustomImage(IDR_THEME_FRAME));
     // Draw a mouse hover gradient for the default themes.
     if (hoverAlpha > 0) {
       if (themeProvider && !hasCustomTheme) {
         base::scoped_nsobject<NSGradient> glow([NSGradient alloc]);
         [glow initWithStartingColor:[NSColor colorWithCalibratedWhite:1.0
                                         alpha:1.0 * hoverAlpha]
                         endingColor:[NSColor colorWithCalibratedWhite:1.0
                                                                 alpha:0.0]];
         NSRect rect = [self bounds];
         NSPoint point = hoverPoint_;
         point.y = NSHeight(rect);
         [glow drawFromCenter:point
                       radius:0.0
                     toCenter:point
                       radius:NSWidth(rect) / 3.0
                      options:NSGradientDrawsBeforeStartingLocation];
       }
     }
 
     CGContextEndTransparencyLayer(cgContext);
   }
 }
 
 // Draws the tab outline.
 - (void)drawStroke:(NSRect)dirtyRect {
-  BOOL focused = [[self window] isMainWindow];
-  CGFloat alpha = focused ? 1.0 : tabs::kImageNoFocusAlpha;
-
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  float height =
-      [rb.GetNativeImageNamed(IDR_TAB_ACTIVE_LEFT).ToNSImage() size].height;
-  if (state_ == NSOnState) {
-    NSDrawThreePartImage(NSMakeRect(0, 0, NSWidth([self bounds]), height),
-        rb.GetNativeImageNamed(IDR_TAB_ACTIVE_LEFT).ToNSImage(),
-        rb.GetNativeImageNamed(IDR_TAB_ACTIVE_CENTER).ToNSImage(),
-        rb.GetNativeImageNamed(IDR_TAB_ACTIVE_RIGHT).ToNSImage(),
-        /*vertical=*/NO,
-        NSCompositeSourceOver,
-        alpha,
-        /*flipped=*/NO);
-  } else {
-    NSDrawThreePartImage(NSMakeRect(0, 0, NSWidth([self bounds]), height),
-        rb.GetNativeImageNamed(IDR_TAB_INACTIVE_LEFT).ToNSImage(),
-        rb.GetNativeImageNamed(IDR_TAB_INACTIVE_CENTER).ToNSImage(),
-        rb.GetNativeImageNamed(IDR_TAB_INACTIVE_RIGHT).ToNSImage(),
-        /*vertical=*/NO,
-        NSCompositeSourceOver,
-        alpha,
-        /*flipped=*/NO);
-  }
+  CGFloat alpha = [[self window] isMainWindow] ? 1.0 : tabs::kImageNoFocusAlpha;
+  GetStrokeImage(state_ == NSOnState)
+      ->DrawInRect([self bounds], NSCompositeSourceOver, alpha);
 }
 
 - (void)drawRect:(NSRect)dirtyRect {
-  // Close button and image are drawn by subviews.
   [self drawFill:dirtyRect];
   [self drawStroke:dirtyRect];
 
   // We draw the title string directly instead of using a NSTextField subview.
   // This is so that we can get font smoothing to work on earlier OS, and even
   // when the tab background is a pattern image (when using themes).
   if (![titleView_ isHidden]) {
     gfx::ScopedNSGraphicsContextSaveGState scopedGState;
     NSGraphicsContext* context = [NSGraphicsContext currentContext];
     CGContextRef cgContext = static_cast<CGContextRef>([context graphicsPort]);
@@ skipping 22 matching lines @@
   if ([self window]) {
     [controller_ updateTitleColor];
   }
 }
 
 - (NSString*)title {
   return [titleView_ stringValue];
 }
 
 - (void)setTitle:(NSString*)title {
+  if ([title isEqualToString:[titleView_ stringValue]])
+    return;
+
   [titleView_ setStringValue:title];
 
   base::string16 title16 = base::SysNSStringToUTF16(title);
   bool isRTL = base::i18n::GetFirstStrongCharacterDirection(title16) ==
                base::i18n::RIGHT_TO_LEFT;
   titleViewCell_.truncateMode = isRTL ? GTMFadeTruncatingHead
                                       : GTMFadeTruncatingTail;
 
   [self setNeedsDisplayInRect:[titleView_ frame]];
 }
 
 - (NSRect)titleFrame {
   return [titleView_ frame];
 }
 
 - (void)setTitleFrame:(NSRect)titleFrame {
+  NSRect oldTitleFrame = [titleView_ frame];
+  if (NSEqualRects(titleFrame, oldTitleFrame))
+    return;
   [titleView_ setFrame:titleFrame];
-  [self setNeedsDisplayInRect:titleFrame];
+  [self setNeedsDisplayInRect:NSUnionRect(titleFrame, oldTitleFrame)];
 }
 
 - (NSColor*)titleColor {
   return [titleView_ textColor];
 }
 
 - (void)setTitleColor:(NSColor*)titleColor {
+  if ([titleColor isEqual:[titleView_ textColor]])
+    return;
   [titleView_ setTextColor:titleColor];
   [self setNeedsDisplayInRect:[titleView_ frame]];
 }
 
 - (BOOL)titleHidden {
   return [titleView_ isHidden];
 }
 
 - (void)setTitleHidden:(BOOL)titleHidden {
+  if (titleHidden == [titleView_ isHidden])
+    return;
   [titleView_ setHidden:titleHidden];
   [self setNeedsDisplayInRect:[titleView_ frame]];
 }
 
 - (void)setState:(NSCellStateValue)state {
   if (state_ == state)
     return;
   state_ = state;
   [self setNeedsDisplay:YES];
 }
@@ skipping 192 matching lines @@
     }
   }
 
   if (nextUpdate < kNoUpdate)
     [self performSelector:_cmd withObject:nil afterDelay:nextUpdate];
 
   [self resetLastGlowUpdateTime];
   [self setNeedsDisplay:YES];
 }
 
-- (CGImageRef)tabClippingMask {
-  // NOTE: NSHeight([self bounds]) doesn't match the height of the bitmaps.
-  CGFloat scale = 1;
-  if ([[self window] respondsToSelector:@selector(backingScaleFactor)])
-    scale = [[self window] backingScaleFactor];
-
-  NSRect bounds = [self bounds];
-  CGFloat tabWidth = NSWidth(bounds);
-  if (tabWidth == maskCacheWidth_ && scale == maskCacheScale_)
-    return maskCache_.get();
-
-  maskCacheWidth_ = tabWidth;
-  maskCacheScale_ = scale;
-
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  NSImage* leftMask = rb.GetNativeImageNamed(IDR_TAB_ALPHA_LEFT).ToNSImage();
-  NSImage* rightMask = rb.GetNativeImageNamed(IDR_TAB_ALPHA_RIGHT).ToNSImage();
-
-  CGFloat leftWidth = leftMask.size.width;
-  CGFloat rightWidth = rightMask.size.width;
-
-  // Image masks must be in the DeviceGray colorspace. Create a context and
-  // draw the mask into it.
-  base::ScopedCFTypeRef<CGColorSpaceRef> colorspace(
-      CGColorSpaceCreateDeviceGray());
-  base::ScopedCFTypeRef<CGContextRef> maskContext(
-      CGBitmapContextCreate(NULL, tabWidth * scale, kMaskHeight * scale,
-                            8, tabWidth * scale, colorspace, 0));
-  CGContextScaleCTM(maskContext, scale, scale);
-  NSGraphicsContext* maskGraphicsContext =
-      [NSGraphicsContext graphicsContextWithGraphicsPort:maskContext
-                                                 flipped:NO];
-
-  gfx::ScopedNSGraphicsContextSaveGState scopedGState;
-  [NSGraphicsContext setCurrentContext:maskGraphicsContext];
-
-  // Draw mask image.
-  [[NSColor blackColor] setFill];
-  CGContextFillRect(maskContext, CGRectMake(0, 0, tabWidth, kMaskHeight));
-
-  NSDrawThreePartImage(NSMakeRect(0, 0, tabWidth, kMaskHeight),
-      leftMask, nil, rightMask, /*vertical=*/NO, NSCompositeSourceOver, 1.0,
-      /*flipped=*/NO);
-
-  CGFloat middleWidth = tabWidth - leftWidth - rightWidth;
-  NSRect middleRect = NSMakeRect(leftWidth, 0, middleWidth, kFillHeight);
-  [[NSColor whiteColor] setFill];
-  NSRectFill(middleRect);
-
-  maskCache_.reset(CGBitmapContextCreateImage(maskContext));
-  return maskCache_;
-}
-
 @end  // @implementation TabView(Private)