Bug 1830667 - Update APZCTreeManager::mDPI when display DPI changes. r=dlrobertson,win-reviewers,handyman,emilio

Differential Revision: https://phabricator.services.mozilla.com/D202280

widget/cocoa/nsCocoaWindow.mm

@@ -2220,6 +2220,7 @@ void nsCocoaWindow::BackingScaleFactorChanged() {
   }
 
   mBackingScaleFactor = newScale;
+  NotifyAPZOfDPIChange();
 
   if (!mWidgetListener || mWidgetListener->GetAppWindow()) {
     return;

widget/gtk/nsWindow.cpp

@@ -5375,6 +5375,7 @@ void nsWindow::OnDPIChanged() {
     }
     mWidgetListener->UIResolutionChanged();
   }
+  NotifyAPZOfDPIChange();
 }
 
 void nsWindow::OnCheckResize() { mPendingConfigures++; }
@@ -5408,6 +5409,8 @@ void nsWindow::OnScaleChanged(bool aNotify) {
     return;
   }
 
+  NotifyAPZOfDPIChange();
+
   LOG("OnScaleChanged %d, %f -> %d, %f\n", int(mCeiledScaleFactor),
       mFractionalScaleFactor, newCeiled, newFractional);
 

widget/nsBaseWidget.cpp

@@ -547,6 +547,12 @@ nsIWidget* nsBaseWidget::GetSheetWindowParent(void) { return nullptr; }
 
 float nsBaseWidget::GetDPI() { return 96.0f; }
 
+void nsBaseWidget::NotifyAPZOfDPIChange() {
+  if (mAPZC) {
+    mAPZC->SetDPI(GetDPI());
+  }
+}
+
 CSSToLayoutDeviceScale nsIWidget::GetDefaultScale() {
   double devPixelsPerCSSPixel = StaticPrefs::layout_css_devPixelsPerPx();
 

widget/nsBaseWidget.h

@@ -354,6 +354,8 @@ class nsBaseWidget : public nsIWidget, public nsSupportsWeakReference {
   // theme changes.
   void NotifyThemeChanged(mozilla::widget::ThemeChangeKind);
 
+  void NotifyAPZOfDPIChange();
+
 #ifdef ACCESSIBILITY
   // Get the accessible for the window.
   mozilla::a11y::LocalAccessible* GetRootAccessible();

widget/windows/nsWindow.cpp

@@ -8536,6 +8536,7 @@ void nsWindow::ChangedDPI() {
       presShell->BackingScaleFactorChanged();
     }
   }
+  NotifyAPZOfDPIChange();
 }
 
 static Result<POINTER_FLAGS, nsresult> PointerStateToFlag(