Bug 1773823 - Remove devPixelsPerPx special cases in LookAndFeel. r=stransky

LookAndFeel::GetFont should always return CSS font sizes.

Differential Revision: https://phabricator.services.mozilla.com/D149491

widget/gtk/nsLookAndFeel.cpp

@@ -1094,16 +1094,8 @@ bool nsLookAndFeel::PerThemeData::GetFont(FontID aID, nsString& aFontName,
       break;
   }
 
-  // Scale the font for the current monitor
-  double scaleFactor = StaticPrefs::layout_css_devPixelsPerPx();
-  if (scaleFactor > 0) {
-    aFontStyle.size *=
-        widget::ScreenHelperGTK::GetGTKMonitorScaleFactor() / scaleFactor;
-  } else {
-    // Convert gdk pixels to CSS pixels.
-    aFontStyle.size /= gfxPlatformGtk::GetFontScaleFactor();
-  }
-
+  // Convert gdk pixels to CSS pixels.
+  aFontStyle.size /= gfxPlatformGtk::GetFontScaleFactor();
   return true;
 }
 

widget/gtk/nsNativeThemeGTK.cpp

@@ -61,22 +61,15 @@ static int gLastGdkError;
 // Return scale factor of the monitor where the window is located
 // by the most part or layout.css.devPixelsPerPx pref if set to > 0.
 static inline gint GetMonitorScaleFactor(nsPresContext* aPresContext) {
-  // When the layout.css.devPixelsPerPx is set the scale can be < 1,
-  // the real monitor scale cannot go under 1.
-  double scale = StaticPrefs::layout_css_devPixelsPerPx();
-  if (scale <= 0) {
-    if (nsCOMPtr<nsIWidget> rootWidget = aPresContext->GetRootWidget()) {
-      int monitorScale = int(round(rootWidget->GetDefaultScale().scale));
-      // Monitor scale can be negative if it has not been initialized in the
-      // puppet widget yet. We also make sure that we return positive value.
-      if (monitorScale < 1) {
-        return 1;
-      }
-      return monitorScale;
-    }
-  }
-  // Use monitor scaling factor where devPixelsPerPx is set
-  return ScreenHelperGTK::GetGTKMonitorScaleFactor();
+  nsCOMPtr<nsIWidget> rootWidget = aPresContext->GetRootWidget();
+  auto scale = rootWidget ? rootWidget->GetDefaultScale()
+                          : aPresContext->CSSToDevPixelScale();
+  // We prefer the root widget scale since it doesn't account for text scale
+  // factor, this is the same scrollbars do in GTK.
+  int monitorScale = int(round(scale.scale));
+  // When the layout.css.devPixelsPerPx is set the scale can be < 1, the real
+  // monitor scale cannot go under 1.
+  return std::max(1, monitorScale);
 }
 
 static inline gint GetMonitorScaleFactor(nsIFrame* aFrame) {