bug 794038 pt 2.0 - respond to changes to backing-store resolution when a window moves between HiDPI and non-HiDPI displays. r=smichaud

docshell/base/nsDocShell.cpp

@@ -5007,6 +5007,13 @@ NS_IMETHODIMP
 nsDocShell::GetPositionAndSize(int32_t * x, int32_t * y, int32_t * cx,
                                int32_t * cy)
 {
+    if (mParentWidget) {
+        // ensure size is up-to-date if window has changed resolution
+        nsIntRect r;
+        mParentWidget->GetClientBounds(r);
+        SetPositionAndSize(mBounds.x, mBounds.y, r.width, r.height, false);
+    }
+
     // We should really consider just getting this information from
     // our window instead of duplicating the storage and code...
     if (cx || cy) {

layout/base/nsIPresShell.h

@@ -1353,6 +1353,7 @@ public:
   virtual void WindowSizeMoveDone() = 0;
   virtual void SysColorChanged() = 0;
   virtual void ThemeChanged() = 0;
+  virtual void BackingScaleFactorChanged() = 0;
 
   nscoord MaxLineBoxWidth() {
     return mMaxLineBoxWidth;

layout/base/nsPresContext.cpp

@@ -1604,6 +1604,45 @@ nsPresContext::SysColorChangedInternal()
   RebuildAllStyleData(nsChangeHint(0));
 }
 
+void
+nsPresContext::UIResolutionChanged()
+{
+  if (!mPendingUIResolutionChanged) {
+    nsCOMPtr<nsIRunnable> ev =
+      NS_NewRunnableMethod(this, &nsPresContext::UIResolutionChangedInternal);
+    if (NS_SUCCEEDED(NS_DispatchToCurrentThread(ev))) {
+      mPendingUIResolutionChanged = true;
+    }
+  }
+}
+
+/*static*/ bool
+nsPresContext::UIResolutionChangedSubdocumentCallback(nsIDocument* aDocument,
+                                                      void* aData)
+{
+  nsIPresShell* shell = aDocument->GetShell();
+  if (shell) {
+    nsPresContext* pc = shell->GetPresContext();
+    if (pc) {
+      pc->UIResolutionChangedInternal();
+    }
+  }
+  return true;
+}
+
+void
+nsPresContext::UIResolutionChangedInternal()
+{
+  mPendingUIResolutionChanged = false;
+
+  if (mDeviceContext->CheckDPIChange()) {
+    AppUnitsPerDevPixelChanged();
+  }
+
+  mDocument->EnumerateSubDocuments(UIResolutionChangedSubdocumentCallback,
+                                   nullptr);
+}
+
 void
 nsPresContext::RebuildAllStyleData(nsChangeHint aExtraHint)
 {

layout/base/nsPresContext.h

@@ -722,6 +722,13 @@ public:
    */
   NS_HIDDEN_(void) ThemeChanged();
 
+  /*
+   * Notify the pres context that the resolution of the user interface has
+   * changed. This happens if a window is moved between HiDPI and non-HiDPI
+   * displays, so that the ratio of points to device pixels changes.
+   */
+  NS_HIDDEN_(void) UIResolutionChanged();
+
   /*
    * Notify the pres context that a system color has changed
    */
@@ -930,6 +937,10 @@ protected:
   friend class nsRunnableMethod<nsPresContext>;
   NS_HIDDEN_(void) ThemeChangedInternal();
   NS_HIDDEN_(void) SysColorChangedInternal();
+  NS_HIDDEN_(void) UIResolutionChangedInternal();
+
+  static NS_HIDDEN_(bool)
+  UIResolutionChangedSubdocumentCallback(nsIDocument* aDocument, void* aData);
 
   NS_HIDDEN_(void) SetImgAnimations(nsIContent *aParent, uint16_t aMode);
   NS_HIDDEN_(void) SetSMILAnimations(nsIDocument *aDoc, uint16_t aNewMode,
@@ -1165,6 +1176,7 @@ protected:
   unsigned              mPrefScrollbarSide : 2;
   unsigned              mPendingSysColorChanged : 1;
   unsigned              mPendingThemeChanged : 1;
+  unsigned              mPendingUIResolutionChanged : 1;
   unsigned              mPendingMediaFeatureValuesChanged : 1;
   unsigned              mPrefChangePendingNeedsReflow : 1;
   unsigned              mMayHaveFixedBackgroundFrames : 1;

layout/base/nsPresShell.h

@@ -697,6 +697,7 @@ protected:
   virtual void WindowSizeMoveDone();
   virtual void SysColorChanged() { mPresContext->SysColorChanged(); }
   virtual void ThemeChanged() { mPresContext->ThemeChanged(); }
+  virtual void BackingScaleFactorChanged() { mPresContext->UIResolutionChanged(); }
 
 #ifdef DEBUG
   // The reflow root under which we're currently reflowing.  Null when

modules/libpref/src/init/all.js

@@ -195,8 +195,8 @@ pref("media.video-queue.default-size", 10);
 // Whether to run in native HiDPI mode on machines with "Retina"/HiDPI display;
 //   <= 0 : hidpi mode disabled, display will just use pixel-based upscaling
 //   == 1 : hidpi supported if all screens share the same backingScaleFactor
-//   >= 2 : hidpi supported even with mixed backingScaleFactors (currently broken)
-pref("gfx.hidpi.enabled", 1);
+//   >= 2 : hidpi supported even with mixed backingScaleFactors (somewhat broken)
+pref("gfx.hidpi.enabled", 2);
 #endif
 
 // 0 = Off, 1 = Full, 2 = Tagged Images Only. 

widget/cocoa/nsChildView.h

@@ -396,6 +396,10 @@ public:
   // pixels" and the Cocoa "points" coordinate system.
   CGFloat                 BackingScaleFactor();
 
+  // Call if the window's backing scale factor changes - i.e., it is moved
+  // between HiDPI and non-HiDPI screens
+  void                    BackingScaleFactorChanged();
+
   virtual double          GetDefaultScale();
 
   NS_IMETHOD              Invalidate(const nsIntRect &aRect);

widget/cocoa/nsChildView.mm

@@ -765,6 +765,29 @@ nsChildView::BackingScaleFactor()
   return mBackingScaleFactor;
 }
 
+void
+nsChildView::BackingScaleFactorChanged()
+{
+  CGFloat newScale = nsCocoaUtils::GetBackingScaleFactor(mView);
+
+  // ignore notification if it hasn't really changed (or maybe we have
+  // disabled HiDPI mode via prefs)
+  if (mBackingScaleFactor == newScale) {
+    return;
+  }
+
+  mBackingScaleFactor = newScale;
+
+  if (!mWidgetListener || mWidgetListener->GetXULWindow()) {
+    return;
+  }
+
+  nsIPresShell* presShell = mWidgetListener->GetPresShell();
+  if (presShell) {
+    presShell->BackingScaleFactorChanged();
+  }
+}
+
 NS_IMETHODIMP nsChildView::ConstrainPosition(bool aAllowSlop,
                                              int32_t *aX, int32_t *aY)
 {
@@ -2347,6 +2370,17 @@ NSEvent* gLastDragMouseDownEvent = nil;
   return nsCocoaUtils::HiDPIEnabled() ? YES : NO;
 }
 
+- (void)viewDidChangeBackingProperties
+{
+  [super viewDidChangeBackingProperties];
+  if (mGeckoChild) {
+    // actually, it could be the color space that's changed,
+    // but we can't tell the difference here except by retrieving
+    // the backing scale factor and comparing to the old value
+    mGeckoChild->BackingScaleFactorChanged();
+  }
+}
+
 // The display system has told us that a portion of our view is dirty. Tell
 // gecko to paint it
 - (void)drawRect:(NSRect)aRect

widget/cocoa/nsCocoaWindow.h

@@ -243,6 +243,7 @@ public:
     NS_IMETHOD              SetCursor(imgIContainer* aCursor, uint32_t aHotspotX, uint32_t aHotspotY);
 
     CGFloat                 BackingScaleFactor();
+    void                    BackingScaleFactorChanged();
     virtual double          GetDefaultScale();
 
     NS_IMETHOD              SetTitle(const nsAString& aTitle);

widget/cocoa/nsCocoaWindow.mm

@@ -30,6 +30,7 @@
 #include "nsCocoaFeatures.h"
 #include "nsIScreenManager.h"
 #include "nsIWidgetListener.h"
+#include "nsIPresShell.h"
 
 #include "gfxPlatform.h"
 #include "qcms.h"
@@ -425,6 +426,10 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
   mWindow = [[windowClass alloc] initWithContentRect:contentRect styleMask:features 
                                  backing:NSBackingStoreBuffered defer:YES];
 
+  // setup our notification delegate. Note that setDelegate: does NOT retain.
+  mDelegate = [[WindowDelegate alloc] initWithGeckoWindow:this];
+  [mWindow setDelegate:mDelegate];
+
   // Make sure that the content rect we gave has been honored.
   NSRect wantedFrame = [mWindow frameRectForContentRect:contentRect];
   if (!NSEqualRects([mWindow frame], wantedFrame)) {
@@ -445,10 +450,6 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
   [mWindow setContentMinSize:NSMakeSize(60, 60)];
   [mWindow disableCursorRects];
 
-  // setup our notification delegate. Note that setDelegate: does NOT retain.
-  mDelegate = [[WindowDelegate alloc] initWithGeckoWindow:this];
-  [mWindow setDelegate:mDelegate];
-
   [[WindowDataMap sharedWindowDataMap] ensureDataForWindow:mWindow];
   mWindowMadeHere = true;
 
@@ -1415,6 +1416,29 @@ nsCocoaWindow::BackingScaleFactor()
   return mBackingScaleFactor;
 }
 
+void
+nsCocoaWindow::BackingScaleFactorChanged()
+{
+  CGFloat newScale = nsCocoaUtils::GetBackingScaleFactor(mWindow);
+
+  // ignore notification if it hasn't really changed (or maybe we have
+  // disabled HiDPI mode via prefs)
+  if (mBackingScaleFactor == newScale) {
+    return;
+  }
+
+  mBackingScaleFactor = newScale;
+
+  if (!mWidgetListener || mWidgetListener->GetXULWindow()) {
+    return;
+  }
+
+  nsIPresShell* presShell = mWidgetListener->GetPresShell();
+  if (presShell) {
+    presShell->BackingScaleFactorChanged();
+  }
+}
+
 NS_IMETHODIMP nsCocoaWindow::SetCursor(nsCursor aCursor)
 {
   if (mPopupContentView)
@@ -2240,6 +2264,24 @@ bool nsCocoaWindow::ShouldFocusPlugin()
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
+- (void)windowDidChangeBackingProperties:(NSNotification *)aNotification
+{
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
+
+  NSWindow *window = (NSWindow *)[aNotification object];
+
+  if ([window respondsToSelector:@selector(backingScaleFactor)]) {
+    CGFloat oldFactor =
+      [[[aNotification userInfo]
+         objectForKey:@"NSBackingPropertyOldScaleFactorKey"] doubleValue];
+    if ([window backingScaleFactor] != oldFactor) {
+      mGeckoWindow->BackingScaleFactorChanged();
+    }
+  }
+
+  NS_OBJC_END_TRY_ABORT_BLOCK;
+}
+
 - (nsCocoaWindow*)geckoWidget
 {
   return mGeckoWindow;