Mac HiDPI: Fix scale factor on external display

content/browser/renderer_host/render_widget_host_view_mac.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.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #include <QuartzCore/QuartzCore.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 350 matching lines @@
 }
 
 RenderWidgetHost* RenderWidgetHostViewMac::GetRenderWidgetHost() const {
   return render_widget_host_;
 }
 
 void RenderWidgetHostViewMac::WasShown() {
   if (!is_hidden_)
     return;
 
-  // Check if the backing scale factor changed while the tab was in the
-  // background.
-  [cocoa_view_ updateTabBackingStoreScaleFactor];
-
   if (web_contents_switch_paint_time_.is_null())
     web_contents_switch_paint_time_ = base::TimeTicks::Now();
   is_hidden_ = false;
   render_widget_host_->WasShown();
 
   // We're messing with the window, so do this to ensure no flashes.
   [[cocoa_view_ window] disableScreenUpdatesUntilFlush];
 }
 
 void RenderWidgetHostViewMac::WasHidden() {
@@ skipping 1044 matching lines @@
 
 - (id)initWithRenderWidgetHostViewMac:(RenderWidgetHostViewMac*)r {
   self = [super initWithFrame:NSZeroRect];
   if (self) {
     editCommand_helper_.reset(new RenderWidgetHostViewMacEditCommandHelper);
     editCommand_helper_->AddEditingSelectorsToClass([self class]);
 
     renderWidgetHostView_.reset(r);
     canBeKeyView_ = YES;
     focusedPluginIdentifier_ = -1;
+    deviceScaleFactor_ = ScaleFactor(self);
 
     // OpenGL support:
     if ([self respondsToSelector:
         @selector(setWantsBestResolutionOpenGLSurface:)]) {
       [self setWantsBestResolutionOpenGLSurface:YES];
     }
     handlingGlobalFrameDidChange_ = NO;
     [[NSNotificationCenter defaultCenter]
         addObserver:self
            selector:@selector(globalFrameDidChange:)
@@ skipping 573 matching lines @@
                name:NSWindowDidChangeScreenNotification
              object:newWindow];
   }
 }
 
 - (void)updateTabBackingStoreScaleFactor {
   if (!renderWidgetHostView_->render_widget_host_)
     return;
 
   float scaleFactor = ScaleFactor(self);
+  if (scaleFactor == deviceScaleFactor_)
+    return;
+  deviceScaleFactor_ = scaleFactor;
+
   BackingStoreMac* backingStore = static_cast<BackingStoreMac*>(
       renderWidgetHostView_->render_widget_host_->GetBackingStore(false));
   if (backingStore)  // NULL in hardware path.
     backingStore->ScaleFactorChanged(scaleFactor);
 
   renderWidgetHostView_->render_widget_host_->SetDeviceScaleFactor(
       scaleFactor);
 }
 
 // http://developer.apple.com/library/mac/#documentation/GraphicsAnimation/Conceptual/HighResolutionOSX/CapturingScreenContents/CapturingScreenContents.html#//apple_ref/doc/uid/TP40012302-CH10-SW4
 - (void)windowDidChangeBackingProperties:(NSNotification*)notification {
   NSWindow* window = (NSWindow*)[notification object];
 
   CGFloat newBackingScaleFactor = [window backingScaleFactor];
   CGFloat oldBackingScaleFactor = [base::mac::ObjCCast<NSNumber>(
       [[notification userInfo] objectForKey:NSBackingPropertyOldScaleFactorKey])
       doubleValue];
   if (newBackingScaleFactor != oldBackingScaleFactor) {
-    // Background tabs check if their scale factor changed when they become
-    // active, in WasShown().
+    // Background tabs check if their scale factor changed when they are added
+    // to a window.
 
     // Allocating a CGLayerRef with the current scale factor immediately from
     // this handler doesn't work. Schedule the backing store update on the
     // next runloop cycle, then things are read for CGLayerRef allocations to
     // work.
     [self performSelector:@selector(updateTabBackingStoreScaleFactor)
                withObject:nil
                afterDelay:0];
   }
 }
@@ skipping 911 matching lines @@
   hasMarkedText_ = NO;
 }
 
 - (void)insertText:(id)string {
   // This is a method on NSTextInput, not NSTextInputClient. But on 10.5, this
   // gets called anyway. Forward to the right method. http://crbug.com/47890
   [self insertText:string replacementRange:NSMakeRange(NSNotFound, 0)];
 }
 
 - (void)viewDidMoveToWindow {
+  if ([self window])
+    [self updateTabBackingStoreScaleFactor];
+
   if (canBeKeyView_) {
     NSWindow* newWindow = [self window];
     // Pointer comparison only, since we don't know if lastWindow_ is still
     // valid.
     if (newWindow) {
       // If we move into a new window, refresh the frame information. We
       // don't need to do it if it was the same window as it used to be in,
       // since that case is covered by WasShown(). We only want to do this for
       // real browser views, not popups.
       if (newWindow != lastWindow_) {
@@ skipping 209 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 @end