Bug 1573992 - Convert layout.css.devPixelsPerPx to static pref. r=njn

Converts layout.css.devPixelsPerPx to a static pref. This one was one of the slightly odd ones; some values were expecting an atomic float, so instead of defining a regular type float it is defined in StaticPrefList.yaml as an AtomicFloat. I am assuming this was the intent of the pref value all along.

Differential Revision: https://phabricator.services.mozilla.com/D42396

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.yaml

@@ -4353,6 +4353,15 @@
   mirror: always
   rust: true
 
+# Set the number of device pixels per CSS pixel. A value <= 0 means choose
+# automatically based on user settings for the platform (e.g., "UI scale factor"
+# on Mac). A positive value is used as-is. This effectively controls the size
+# of a CSS "px". This is only used for windows on the screen, not for printing.
+- name: layout.css.devPixelsPerPx
+  type: AtomicFloat
+  value: -1.0f
+  mirror: always
+
 # text underline offset
 - name: layout.css.text-underline-offset.enabled
   type: bool

modules/libpref/init/all.js

@@ -2868,12 +2868,6 @@ pref("layout.css.report_errors", true);
 // interpretation of physical units such as "pt".
 pref("layout.css.dpi", -1);
 
-// Set the number of device pixels per CSS pixel. A value <= 0 means choose
-// automatically based on user settings for the platform (e.g., "UI scale factor"
-// on Mac). A positive value is used as-is. This effectively controls the size
-// of a CSS "px". This is only used for windows on the screen, not for printing.
-pref("layout.css.devPixelsPerPx", "-1.0");
-
 // Set the threshold distance in CSS pixels below which scrolling will snap to
 // an edge, when scroll snapping is set to "proximity".
 pref("layout.css.scroll-snap.proximity-threshold", 200);

widget/Screen.cpp

@@ -7,6 +7,7 @@
 #include "Screen.h"
 
 #include "mozilla/dom/DOMTypes.h"
+#include "mozilla/StaticPrefs_layout.h"
 
 namespace mozilla {
 namespace widget {
@@ -103,7 +104,7 @@ Screen::GetContentsScaleFactor(double* aOutScale) {
 
 NS_IMETHODIMP
 Screen::GetDefaultCSSScaleFactor(double* aOutScale) {
-  double scale = nsIWidget::DefaultScaleOverride();
+  double scale = StaticPrefs::layout_css_devPixelsPerPx();
   if (scale > 0.0) {
     *aOutScale = scale;
   } else {

widget/gtk/nsLookAndFeel.cpp

@@ -20,6 +20,7 @@
 #include "gfxPlatformGtk.h"
 #include "mozilla/FontPropertyTypes.h"
 #include "mozilla/RelativeLuminanceUtils.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "ScreenHelperGTK.h"
 
 #include "gtkdrawing.h"
@@ -812,7 +813,7 @@ bool nsLookAndFeel::GetFontImpl(FontID aID, nsString& aFontName,
   }
 
   // Scale the font for the current monitor
-  double scaleFactor = nsIWidget::DefaultScaleOverride();
+  double scaleFactor = StaticPrefs::layout_css_devPixelsPerPx();
   if (scaleFactor > 0) {
     aFontStyle.size *=
         widget::ScreenHelperGTK::GetGTKMonitorScaleFactor() / scaleFactor;

widget/gtk/nsNativeThemeGTK.cpp

@@ -73,7 +73,7 @@ static int gLastGdkError;
 static inline gint GetMonitorScaleFactor(nsIFrame* aFrame) {
   // When the layout.css.devPixelsPerPx is set the scale can be < 1,
   // the real monitor scale cannot go under 1.
-  double scale = nsIWidget::DefaultScaleOverride();
+  double scale = StaticPrefs::layout_css_devPixelsPerPx();
   if (scale <= 0) {
     nsIWidget* rootWidget = aFrame->PresContext()->GetRootWidget();
     if (rootWidget) {

widget/nsBaseWidget.cpp

@@ -72,6 +72,7 @@
 #include "mozilla/gfx/gfxVars.h"
 #include "mozilla/Move.h"
 #include "mozilla/Sprintf.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/webrender/WebRenderTypes.h"
 #include "nsRefPtrHashtable.h"
 #include "TouchEvents.h"
@@ -517,7 +518,7 @@ nsIWidget* nsBaseWidget::GetSheetWindowParent(void) { return nullptr; }
 float nsBaseWidget::GetDPI() { return 96.0f; }
 
 CSSToLayoutDeviceScale nsIWidget::GetDefaultScale() {
-  double devPixelsPerCSSPixel = DefaultScaleOverride();
+  double devPixelsPerCSSPixel = StaticPrefs::layout_css_devPixelsPerPx();
 
   if (devPixelsPerCSSPixel <= 0.0) {
     devPixelsPerCSSPixel = GetDefaultScaleInternal();
@@ -526,23 +527,6 @@ CSSToLayoutDeviceScale nsIWidget::GetDefaultScale() {
   return CSSToLayoutDeviceScale(devPixelsPerCSSPixel);
 }
 
-/* static */
-double nsIWidget::DefaultScaleOverride() {
-  // The number of device pixels per CSS pixel. A value <= 0 means choose
-  // automatically based on the DPI. A positive value is used as-is. This
-  // effectively controls the size of a CSS "px".
-  static float devPixelsPerCSSPixel = -1.0f;
-
-  static bool valueCached = false;
-  if (!valueCached) {
-    Preferences::AddFloatVarCache(&devPixelsPerCSSPixel,
-                                  "layout.css.devPixelsPerPx", -1.0f);
-    valueCached = true;
-  }
-
-  return devPixelsPerCSSPixel;
-}
-
 //-------------------------------------------------------------------------
 //
 // Add a child to the list of children

widget/windows/TaskbarPreview.cpp

@@ -25,6 +25,7 @@
 #include "mozilla/dom/HTMLCanvasElement.h"
 #include "mozilla/gfx/2D.h"
 #include "mozilla/gfx/DataSurfaceHelpers.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/Telemetry.h"
 
 // Defined in dwmapi in a header that needs a higher numbered _WINNT #define
@@ -232,7 +233,7 @@ TaskbarPreview::WndProc(UINT nMsg, WPARAM wParam, LPARAM lParam) {
       rv = mController->GetHeight(&height);
       if (NS_FAILED(rv)) break;
 
-      double scale = nsIWidget::DefaultScaleOverride();
+      double scale = StaticPrefs::layout_css_devPixelsPerPx();
       if (scale <= 0.0) {
         scale = WinUtils::LogToPhysFactor(PreviewWindow());
       }

widget/windows/nsNativeThemeWin.cpp

@@ -1494,7 +1494,7 @@ static bool AssumeThemePartAndStateAreTransparent(int32_t aPart,
 // the system default resolution.
 static inline double GetThemeDpiScaleFactor(nsIFrame* aFrame) {
   if (WinUtils::IsPerMonitorDPIAware() ||
-      nsIWidget::DefaultScaleOverride() > 0.0) {
+      StaticPrefs::layout_css_devPixelsPerPx() > 0.0) {
     nsIWidget* rootWidget = aFrame->PresContext()->GetRootWidget();
     if (rootWidget) {
       double systemScale = WinUtils::SystemScaleFactor();

widget/windows/nsWindow.cpp

@@ -146,6 +146,7 @@
 #include "InProcessWinCompositorWidget.h"
 #include "InputDeviceUtils.h"
 #include "ScreenHelperWin.h"
+#include "mozilla/StaticPrefs_layout.h"
 
 #include "nsIGfxInfo.h"
 #include "nsUXThemeConstants.h"
@@ -7227,7 +7228,7 @@ void nsWindow::OnDPIChanged(int32_t x, int32_t y, int32_t width,
   if (mWindowType == eWindowType_popup) {
     return;
   }
-  if (DefaultScaleOverride() > 0.0) {
+  if (StaticPrefs::layout_css_devPixelsPerPx() > 0.0) {
     return;
   }
   mDefaultScale = -1.0;  // force recomputation of scale factor