Mac HiDPI: Fix scale factor on external display

On Mac OS 10.8, opening a page on external monitor would cause the page to be rendered at the scale factor of the primary display.

The problem is in RenderViewHostImpl::CreateRenderView. It uses the view to calculate the display scale factor but this doesn't work because the view hasn't been added to a window yet.

My fix is to update the scale factor when -[RenderWidgetHostViewCocoa viewDidMoveToWindow:] is called. This CL also caches the scale factor.

Note, for some reason I can't reproduce the bug on 10.7. On 10.7 the scale factor is also incorrect but for some reason the page is displayed correctly. I'm not sure what's going on.

BUG=138039
TBR=sky

Review URL: https://chromiumcodereview.appspot.com/10837154

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150973 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_widget_host_view_mac.h

@@ -139,6 +139,9 @@ class RenderWidgetHostViewMacEditCommandHelper;
 
   // recursive globalFrameDidChange protection:
   BOOL handlingGlobalFrameDidChange_;
+
+  // The scale factor of the display this view is in.
+  float deviceScaleFactor_;
 }
 
 @property(nonatomic, readonly) NSRange selectedRange;

content/browser/renderer_host/render_widget_host_view_mac.mm

@@ -374,10 +374,6 @@ 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;
@@ -1469,6 +1465,7 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
     renderWidgetHostView_.reset(r);
     canBeKeyView_ = YES;
     focusedPluginIdentifier_ = -1;
+    deviceScaleFactor_ = ScaleFactor(self);
 
     // OpenGL support:
     if ([self respondsToSelector:
@@ -2062,6 +2059,10 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
     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.
@@ -2080,8 +2081,8 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
       [[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
@@ -3020,6 +3021,9 @@ extern NSString *NSTextInputReplacementRangeAttributeName;
 }
 
 - (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

ui/base/layout_mac.mm

@@ -17,18 +17,20 @@
 namespace {
 
 float GetScaleFactorScaleForNativeView(gfx::NativeView view) {
-  float scale_factor = 1.0f;
   if (NSWindow* window = [view window]) {
     if ([window respondsToSelector:@selector(backingScaleFactor)])
       return [window backingScaleFactor];
-    scale_factor = [window userSpaceScaleFactor];
+    return [window userSpaceScaleFactor];
   }
-  if (NSScreen* screen = [NSScreen mainScreen]) {
-    if ([screen respondsToSelector:@selector(backingScaleFactor)])
-      return [screen backingScaleFactor];
-    return [screen userSpaceScaleFactor];
-  }
-  return 1.0f;
+
+  NSArray* screens = [NSScreen screens];
+  if (![screens count])
+    return 1.0f;
+
+  NSScreen* screen = [screens objectAtIndex:0];
+  if ([screen respondsToSelector:@selector(backingScaleFactor)])
+    return [screen backingScaleFactor];
+  return [screen userSpaceScaleFactor];
 }
 
 }  // namespace