path: root/mozilla-975919-gtk3-hidpi.patch

# HG changeset patch
# Parent 7b33ee7fd162d784f382250d3fa811e86a1b7348
# User Andrew Comminos <andrew@morlunk.com>
Bug 975919 - Added support for HiDPI on GTK 3.10+

diff --git a/widget/gtk/nsGtkUtils.h b/widget/gtk/nsGtkUtils.h
--- a/widget/gtk/nsGtkUtils.h
+++ b/widget/gtk/nsGtkUtils.h
@@ -4,16 +4,17 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef nsGtkUtils_h__
 #define nsGtkUtils_h__
 
 #include <glib.h>
+#include <dlfcn.h>
 
 // Some gobject functions expect functions for gpointer arguments.
 // gpointer is void* but C++ doesn't like casting functions to void*.
 template<class T> static inline gpointer
 FuncToGpointer(T aFunction)
 {
     return reinterpret_cast<gpointer>
         (reinterpret_cast<uintptr_t>
diff --git a/widget/gtk/nsLookAndFeel.cpp b/widget/gtk/nsLookAndFeel.cpp
--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -728,16 +728,27 @@ GetSystemFontInfo(GtkWidget *aWidget,
 
     // |size| is now either pixels or pango-points (not Mozilla-points!)
 
     if (!pango_font_description_get_size_is_absolute(desc)) {
         // |size| is in pango-points, so convert to pixels.
         size *= float(gfxPlatformGtk::GetDPI()) / POINTS_PER_INCH_FLOAT;
     }
 
+    // Scale fonts up on HiDPI displays.
+    // This would be done automatically with cairo, but we manually manage
+    // the display scale for platform consistency.
+    static gint (*GdkScreenGetMonitorScaleFactorPtr)(GdkScreen*,gint) =
+        (gint (*)(GdkScreen*,gint)) dlsym(RTLD_DEFAULT,
+        "gdk_screen_get_monitor_scale_factor");
+    if (GdkScreenGetMonitorScaleFactorPtr) {
+        GdkScreen *screen = gdk_screen_get_default();
+        size *= (*GdkScreenGetMonitorScaleFactorPtr)(screen, 0);
+    }
+
     // |size| is now pixels
 
     aFontStyle->size = size;
 
     pango_font_description_free(desc);
 }
 
 static void
diff --git a/widget/gtk/nsScreenGtk.cpp b/widget/gtk/nsScreenGtk.cpp
--- a/widget/gtk/nsScreenGtk.cpp
+++ b/widget/gtk/nsScreenGtk.cpp
@@ -6,20 +6,20 @@
 #include "nsScreenGtk.h"
 
 #include <gdk/gdk.h>
 #ifdef MOZ_X11
 #include <gdk/gdkx.h>
 #include <X11/Xatom.h>
 #endif
 #include <gtk/gtk.h>
+#include <dlfcn.h>
 
 static uint32_t sScreenId = 0;
 
-
 nsScreenGtk :: nsScreenGtk (  )
   : mScreenNum(0),
     mRect(0, 0, 0, 0),
     mAvailRect(0, 0, 0, 0),
     mId(++sScreenId)
 {
 }
 
@@ -35,37 +35,68 @@ nsScreenGtk :: GetId(uint32_t *aId)
   *aId = mId;
   return NS_OK;
 } // GetId
 
 
 NS_IMETHODIMP
 nsScreenGtk :: GetRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
 {
+  double scale;
+  GetContentsScaleFactor(&scale);
+
+  *outLeft = NSToIntRound(mRect.x * scale);
+  *outTop = NSToIntRound(mRect.y * scale);
+  *outWidth = NSToIntRound(mRect.width * scale);
+  *outHeight = NSToIntRound(mRect.height * scale);
+
+  return NS_OK;
+  
+} // GetRect
+
+
+NS_IMETHODIMP
+nsScreenGtk :: GetAvailRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
+  double scale;
+  GetContentsScaleFactor(&scale);
+
+  *outLeft = NSToIntRound(mAvailRect.x * scale);
+  *outTop = NSToIntRound(mAvailRect.y * scale);
+  *outWidth = NSToIntRound(mAvailRect.width * scale);
+  *outHeight = NSToIntRound(mAvailRect.height * scale);
+
+  return NS_OK;
+  
+} // GetAvailRect
+
+NS_IMETHODIMP
+nsScreenGtk :: GetRectDisplayPix(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
   *outLeft = mRect.x;
   *outTop = mRect.y;
   *outWidth = mRect.width;
   *outHeight = mRect.height;
 
   return NS_OK;
   
-} // GetRect
+} // GetRectDisplayPix
 
 
 NS_IMETHODIMP
-nsScreenGtk :: GetAvailRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+nsScreenGtk :: GetAvailRectDisplayPix(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
 {
   *outLeft = mAvailRect.x;
   *outTop = mAvailRect.y;
   *outWidth = mAvailRect.width;
   *outHeight = mAvailRect.height;
 
   return NS_OK;
   
-} // GetAvailRect
+} // GetAvailRectDisplayPix
 
 
 NS_IMETHODIMP 
 nsScreenGtk :: GetPixelDepth(int32_t *aPixelDepth)
 {
   GdkVisual * visual = gdk_screen_get_system_visual(gdk_screen_get_default());
   *aPixelDepth = gdk_visual_get_depth(visual);
 
@@ -77,16 +108,33 @@ nsScreenGtk :: GetPixelDepth(int32_t *aP
 NS_IMETHODIMP 
 nsScreenGtk :: GetColorDepth(int32_t *aColorDepth)
 {
   return GetPixelDepth ( aColorDepth );
 
 } // GetColorDepth
 
 
+NS_IMETHODIMP
+nsScreenGtk :: GetContentsScaleFactor(double* aContentsScaleFactor)
+{
+  static gint (*GdkScreenGetMonitorScaleFactorPtr)(GdkScreen*,gint) =
+    (gint (*)(GdkScreen*,gint)) dlsym(RTLD_DEFAULT,
+    "gdk_screen_get_monitor_scale_factor");
+  if (GdkScreenGetMonitorScaleFactorPtr) {
+    GdkScreen *screen = gdk_screen_get_default();
+    *aContentsScaleFactor = (*GdkScreenGetMonitorScaleFactorPtr)
+                            (screen, mScreenNum);
+  } else {
+    *aContentsScaleFactor = 1;
+  }
+  return NS_OK;
+}
+
+
 void
 nsScreenGtk :: Init (GdkWindow *aRootWindow)
 {
   // We listen for configure events on the root window to pick up
   // changes to this rect.  We could listen for "size_changed" signals
   // on the default screen to do this, except that doesn't work with
   // versions of GDK predating the GdkScreen object.  See bug 256646.
   mAvailRect = mRect = nsIntRect(0, 0, gdk_screen_width(), gdk_screen_height());
diff --git a/widget/gtk/nsScreenGtk.h b/widget/gtk/nsScreenGtk.h
--- a/widget/gtk/nsScreenGtk.h
+++ b/widget/gtk/nsScreenGtk.h
@@ -28,18 +28,21 @@ class nsScreenGtk : public nsBaseScreen
 {
 public:
   nsScreenGtk();
   ~nsScreenGtk();
 
   NS_IMETHOD GetId(uint32_t* aId);
   NS_IMETHOD GetRect(int32_t* aLeft, int32_t* aTop, int32_t* aWidth, int32_t* aHeight);
   NS_IMETHOD GetAvailRect(int32_t* aLeft, int32_t* aTop, int32_t* aWidth, int32_t* aHeight);
+  NS_IMETHOD GetRectDisplayPix(int32_t* aLeft, int32_t* aTop, int32_t* aWidth, int32_t* aHeight);
+  NS_IMETHOD GetAvailRectDisplayPix(int32_t* aLeft, int32_t* aTop, int32_t* aWidth, int32_t* aHeight);
   NS_IMETHOD GetPixelDepth(int32_t* aPixelDepth);
   NS_IMETHOD GetColorDepth(int32_t* aColorDepth);
+  NS_IMETHOD GetContentsScaleFactor(double* aContentsScaleFactor);
 
   void Init(GdkWindow *aRootWindow);
 #ifdef MOZ_X11
   void Init(XineramaScreenInfo *aScreenInfo);
 #endif /* MOZ_X11 */
 
 private:
   uint32_t mScreenNum;
diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -466,16 +466,19 @@ nsWindow::DispatchResized(int32_t aWidth
 
 nsresult
 nsWindow::DispatchEvent(WidgetGUIEvent* aEvent, nsEventStatus& aStatus)
 {
 #ifdef DEBUG
     debug_DumpEvent(stdout, aEvent->widget, aEvent,
                     nsAutoCString("something"), 0);
 #endif
+    // Translate the mouse event into device pixels.
+    aEvent->refPoint.x = GdkCoordToDevicePixels(aEvent->refPoint.x);
+    aEvent->refPoint.y = GdkCoordToDevicePixels(aEvent->refPoint.y);
 
     aStatus = nsEventStatus_eIgnore;
     nsIWidgetListener* listener =
         mAttachedWidgetListener ? mAttachedWidgetListener : mWidgetListener;
     if (listener) {
       aStatus = listener->HandleEvent(aEvent, mUseAttachedEvents);
     }
 
@@ -724,16 +727,22 @@ nsWindow::GetDPI()
     double heightInches = DisplayHeightMM(dpy, defaultScreen)/MM_PER_INCH_FLOAT;
     if (heightInches < 0.25) {
         // Something's broken, but we'd better not crash.
         return 96.0f;
     }
     return float(DisplayHeight(dpy, defaultScreen)/heightInches);
 }
 
+double
+nsWindow::GetDefaultScaleInternal()
+{
+    return GdkScaleFactor();
+}
+
 NS_IMETHODIMP
 nsWindow::SetParent(nsIWidget *aNewParent)
 {
     if (mContainer || !mGdkWindow) {
         NS_NOTREACHED("nsWindow::SetParent called illegally");
         return NS_ERROR_NOT_IMPLEMENTED;
     }
 
@@ -822,18 +831,19 @@ nsWindow::ReparentNativeWidgetInternal(n
             SetWidgetForHierarchy(mGdkWindow, aOldContainer, aNewContainer);
 
             if (aOldContainer == gInvisibleContainer) {
                 CheckDestroyInvisibleContainer();
             }
         }
 
         if (!mIsTopLevel) {
-            gdk_window_reparent(mGdkWindow, aNewParentWindow, mBounds.x,
-                                mBounds.y);
+            gdk_window_reparent(mGdkWindow, aNewParentWindow,
+                                DevicePixelsToGdkCoordRoundDown(mBounds.x),
+                                DevicePixelsToGdkCoordRoundDown(mBounds.y));
         }
     }
 
     nsWindow* newParent = static_cast<nsWindow*>(aNewParent);
     bool parentHasMappedToplevel =
         newParent && newParent->mHasMappedToplevel;
     if (mHasMappedToplevel != parentHasMappedToplevel) {
         SetHasMappedToplevel(parentHasMappedToplevel);
@@ -858,52 +868,56 @@ nsWindow::IsVisible() const
 {
     return mIsShown;
 }
 
 NS_IMETHODIMP
 nsWindow::ConstrainPosition(bool aAllowSlop, int32_t *aX, int32_t *aY)
 {
     if (mIsTopLevel && mShell) {
-        int32_t screenWidth = gdk_screen_width();
-        int32_t screenHeight = gdk_screen_height();
+        int width = GdkCoordToDevicePixels(gdk_screen_width());
+        int height = GdkCoordToDevicePixels(gdk_screen_height());
         if (aAllowSlop) {
             if (*aX < (kWindowPositionSlop - mBounds.width))
                 *aX = kWindowPositionSlop - mBounds.width;
-            if (*aX > (screenWidth - kWindowPositionSlop))
-                *aX = screenWidth - kWindowPositionSlop;
+            if (*aX > (width - kWindowPositionSlop))
+                *aX = width - kWindowPositionSlop;
             if (*aY < (kWindowPositionSlop - mBounds.height))
                 *aY = kWindowPositionSlop - mBounds.height;
-            if (*aY > (screenHeight - kWindowPositionSlop))
-                *aY = screenHeight - kWindowPositionSlop;
+            if (*aY > (height - kWindowPositionSlop))
+                *aY = height - kWindowPositionSlop;
         } else {
             if (*aX < 0)
                 *aX = 0;
-            if (*aX > (screenWidth - mBounds.width))
-                *aX = screenWidth - mBounds.width;
+            if (*aX > (width - mBounds.width))
+                *aX = width - mBounds.width;
             if (*aY < 0)
                 *aY = 0;
-            if (*aY > (screenHeight - mBounds.height))
-                *aY = screenHeight - mBounds.height;
+            if (*aY > (height - mBounds.height))
+                *aY = height - mBounds.height;
         }
     }
     return NS_OK;
 }
 
 void nsWindow::SetSizeConstraints(const SizeConstraints& aConstraints)
 {
     mSizeConstraints.mMinSize = GetSafeWindowSize(aConstraints.mMinSize);
     mSizeConstraints.mMaxSize = GetSafeWindowSize(aConstraints.mMaxSize);
 
     if (mShell) {
         GdkGeometry geometry;
-        geometry.min_width = mSizeConstraints.mMinSize.width;
-        geometry.min_height = mSizeConstraints.mMinSize.height;
-        geometry.max_width = mSizeConstraints.mMaxSize.width;
-        geometry.max_height = mSizeConstraints.mMaxSize.height;
+        geometry.min_width = DevicePixelsToGdkCoordRoundUp(
+                             mSizeConstraints.mMinSize.width);
+        geometry.min_height = DevicePixelsToGdkCoordRoundUp(
+                              mSizeConstraints.mMinSize.height);
+        geometry.max_width = DevicePixelsToGdkCoordRoundUp(
+                             mSizeConstraints.mMaxSize.width);
+        geometry.max_height = DevicePixelsToGdkCoordRoundUp(
+                              mSizeConstraints.mMaxSize.height);
 
         uint32_t hints = GDK_HINT_MIN_SIZE | GDK_HINT_MAX_SIZE;
         gtk_window_set_geometry_hints(GTK_WINDOW(mShell), nullptr,
                                       &geometry, GdkWindowHints(hints));
     }
 }
 
 NS_IMETHODIMP
@@ -1156,21 +1170,23 @@ nsWindow::Move(double aX, double aY)
     mBounds.x = x;
     mBounds.y = y;
 
     if (!mCreated)
         return NS_OK;
 
     mNeedsMove = false;
 
+    GdkPoint point = DevicePixelsToGdkPointRoundDown(nsIntPoint(x, y));
+
     if (mIsTopLevel) {
-        gtk_window_move(GTK_WINDOW(mShell), x, y);
+        gtk_window_move(GTK_WINDOW(mShell), point.x, point.y);
     }
     else if (mGdkWindow) {
-        gdk_window_move(mGdkWindow, x, y);
+        gdk_window_move(mGdkWindow, point.x, point.y);
     }
 
     NotifyRollupGeometryChange();
     return NS_OK;
 }
 
 NS_IMETHODIMP
 nsWindow::PlaceBehind(nsTopLevelWidgetZPlacement  aPlacement,
@@ -1427,17 +1443,17 @@ nsWindow::SetFocus(bool aRaise)
 
 NS_IMETHODIMP
 nsWindow::GetScreenBounds(nsIntRect &aRect)
 {
     if (mIsTopLevel && mContainer) {
         // use the point including window decorations
         gint x, y;
         gdk_window_get_root_origin(gtk_widget_get_window(GTK_WIDGET(mContainer)), &x, &y);
-        aRect.MoveTo(x, y);
+        aRect.MoveTo(GdkPointToDevicePixels({ x, y }));
     }
     else {
         aRect.MoveTo(WidgetToScreenOffset());
     }
     // mBounds.Size() is the window bounds, not the window-manager frame
     // bounds (bug 581863).  gdk_window_get_frame_extents would give the
     // frame bounds, but mBounds.Size() is returned here for consistency
     // with Resize.
@@ -1597,27 +1613,22 @@ nsWindow::SetCursor(imgIContainer* aCurs
 }
 
 NS_IMETHODIMP
 nsWindow::Invalidate(const nsIntRect &aRect)
 {
     if (!mGdkWindow)
         return NS_OK;
 
-    GdkRectangle rect;
-    rect.x = aRect.x;
-    rect.y = aRect.y;
-    rect.width = aRect.width;
-    rect.height = aRect.height;
+    GdkRectangle rect = DevicePixelsToGdkRectRoundOut(aRect);
+    gdk_window_invalidate_rect(mGdkWindow, &rect, FALSE);
 
     LOGDRAW(("Invalidate (rect) [%p]: %d %d %d %d\n", (void *)this,
              rect.x, rect.y, rect.width, rect.height));
 
-    gdk_window_invalidate_rect(mGdkWindow, &rect, FALSE);
-
     return NS_OK;
 }
 
 void*
 nsWindow::GetNativeData(uint32_t aDataType)
 {
     switch (aDataType) {
     case NS_NATIVE_WINDOW:
@@ -1745,17 +1756,17 @@ nsIntPoint
 nsWindow::WidgetToScreenOffset()
 {
     gint x = 0, y = 0;
 
     if (mGdkWindow) {
         gdk_window_get_origin(mGdkWindow, &x, &y);
     }
 
-    return nsIntPoint(x, y);
+    return GdkPointToDevicePixels({ x, y });
 }
 
 NS_IMETHODIMP
 nsWindow::EnableDragDrop(bool aEnable)
 {
     return NS_OK;
 }
 
@@ -2037,17 +2048,19 @@ nsWindow::OnExposeEvent(cairo_t *cr)
 #if (MOZ_WIDGET_GTK == 2)
     if (!exposeRegion.Init(aEvent)) {
 #else
     if (!exposeRegion.Init(cr)) {
 #endif
         return FALSE;
     }
 
-    nsIntRegion &region = exposeRegion.mRegion;
+    gint scale = GdkScaleFactor();
+    nsIntRegion& region = exposeRegion.mRegion;
+    region.ScaleRoundOut(scale, scale);
 
     ClientLayerManager *clientLayers =
         (GetLayerManager()->GetBackendType() == LayersBackend::LAYERS_CLIENT)
         ? static_cast<ClientLayerManager*>(GetLayerManager())
         : nullptr;
 
     if (clientLayers && mCompositorParent) {
         // We need to paint to the screen even if nothing changed, since if we
@@ -2377,31 +2390,34 @@ nsWindow::OnContainerUnrealize()
 
 void
 nsWindow::OnSizeAllocate(GtkAllocation *aAllocation)
 {
     LOG(("size_allocate [%p] %d %d %d %d\n",
          (void *)this, aAllocation->x, aAllocation->y,
          aAllocation->width, aAllocation->height));
 
-    nsIntSize size(aAllocation->width, aAllocation->height);
+    nsIntSize size = GdkRectToDevicePixels(*aAllocation).Size();
+
     if (mBounds.Size() == size)
         return;
 
+    nsIntRect rect;
+
     // Invalidate the new part of the window now for the pending paint to
     // minimize background flashes (GDK does not do this for external resizes
     // of toplevels.)
     if (mBounds.width < size.width) {
-        GdkRectangle rect =
-            { mBounds.width, 0, size.width - mBounds.width, size.height };
+        GdkRectangle rect = DevicePixelsToGdkRectRoundOut(
+            { mBounds.width, 0, size.width - mBounds.width, size.height });
         gdk_window_invalidate_rect(mGdkWindow, &rect, FALSE);
     }
     if (mBounds.height < size.height) {
-        GdkRectangle rect =
-            { 0, mBounds.height, size.width, size.height - mBounds.height };
+        GdkRectangle rect = DevicePixelsToGdkRectRoundOut(
+            { 0, mBounds.height, size.width, size.height - mBounds.height });
         gdk_window_invalidate_rect(mGdkWindow, &rect, FALSE);
     }
 
     mBounds.SizeTo(size);
 
     if (!mGdkWindow)
         return;
 
@@ -3843,67 +3859,75 @@ nsWindow::SetWindowClass(const nsAString
   nsMemory::Free(res_name);
 
   return NS_OK;
 }
 
 void
 nsWindow::NativeResize(int32_t aWidth, int32_t aHeight, bool    aRepaint)
 {
+    gint width = DevicePixelsToGdkCoordRoundUp(aWidth);
+    gint height = DevicePixelsToGdkCoordRoundUp(aHeight);
+    
     LOG(("nsWindow::NativeResize [%p] %d %d\n", (void *)this,
-         aWidth, aHeight));
+         width, height));
 
     // clear our resize flag
     mNeedsResize = false;
 
     if (mIsTopLevel) {
-        gtk_window_resize(GTK_WINDOW(mShell), aWidth, aHeight);
+        gtk_window_resize(GTK_WINDOW(mShell), width, height);
     }
     else if (mContainer) {
         GtkWidget *widget = GTK_WIDGET(mContainer);
         GtkAllocation allocation, prev_allocation;
         gtk_widget_get_allocation(widget, &prev_allocation);
         allocation.x = prev_allocation.x;
         allocation.y = prev_allocation.y;
-        allocation.width = aWidth;
-        allocation.height = aHeight;
+        allocation.width = width;
+        allocation.height = height;
         gtk_widget_size_allocate(widget, &allocation);
     }
     else if (mGdkWindow) {
-        gdk_window_resize(mGdkWindow, aWidth, aHeight);
+        gdk_window_resize(mGdkWindow, width, height);
     }
 }
 
 void
 nsWindow::NativeResize(int32_t aX, int32_t aY,
                        int32_t aWidth, int32_t aHeight,
                        bool    aRepaint)
 {
+    gint width = DevicePixelsToGdkCoordRoundUp(aWidth);
+    gint height = DevicePixelsToGdkCoordRoundUp(aHeight);
+    gint x = DevicePixelsToGdkCoordRoundDown(aX);
+    gint y = DevicePixelsToGdkCoordRoundDown(aY);
+
     mNeedsResize = false;
     mNeedsMove = false;
 
     LOG(("nsWindow::NativeResize [%p] %d %d %d %d\n", (void *)this,
-         aX, aY, aWidth, aHeight));
+         x, y, width, height));
 
     if (mIsTopLevel) {
-        // aX and aY give the position of the window manager frame top-left.
-        gtk_window_move(GTK_WINDOW(mShell), aX, aY);
+        // x and y give the position of the window manager frame top-left.
+        gtk_window_move(GTK_WINDOW(mShell), x, y);
         // This sets the client window size.
-        gtk_window_resize(GTK_WINDOW(mShell), aWidth, aHeight);
+        gtk_window_resize(GTK_WINDOW(mShell), width, height);
     }
     else if (mContainer) {
         GtkAllocation allocation;
-        allocation.x = aX;
-        allocation.y = aY;
-        allocation.width = aWidth;
-        allocation.height = aHeight;
+        allocation.x = x;
+        allocation.y = y;
+        allocation.width = width;
+        allocation.height = height;
         gtk_widget_size_allocate(GTK_WIDGET(mContainer), &allocation);
     }
     else if (mGdkWindow) {
-        gdk_window_move_resize(mGdkWindow, aX, aY, aWidth, aHeight);
+        gdk_window_move_resize(mGdkWindow, x, y, width, height);
     }
 }
 
 void
 nsWindow::NativeShow(bool aAction)
 {
     if (aAction) {
         // unset our flag now that our window has been shown
@@ -6178,18 +6202,18 @@ nsWindow::GetThebesSurface(cairo_t *cr)
 #if (MOZ_WIDGET_GTK == 2)
     gdk_drawable_get_size(GDK_DRAWABLE(mGdkWindow), &width, &height);
 #else
     width = gdk_window_get_width(mGdkWindow);
     height = gdk_window_get_height(mGdkWindow);
 #endif
 
     // Owen Taylor says this is the right thing to do!
-    width = std::min(32767, width);
-    height = std::min(32767, height);
+    width = std::min(32767, (int)std::ceil(GdkCoordToDevicePixels(width)));
+    height = std::min(32767, (int)std::ceil(GdkCoordToDevicePixels(height)));
     gfxIntSize size(width, height);
 
     GdkVisual *gdkVisual = gdk_window_get_visual(mGdkWindow);
     Visual* visual = gdk_x11_visual_get_xvisual(gdkVisual);
 
 #  ifdef MOZ_HAVE_SHMIMAGE
     bool usingShm = false;
     if (nsShmImage::UseShm()) {
@@ -6204,18 +6228,27 @@ nsWindow::GetThebesSurface(cairo_t *cr)
     }
     if (!usingShm)
 #  endif  // MOZ_HAVE_SHMIMAGE
     {
 #if (MOZ_WIDGET_GTK == 3)
 #if MOZ_TREE_CAIRO
 #error "cairo-gtk3 target must be built with --enable-system-cairo"
 #else    
+    // Available as of Cairo 1.14
+    static void (*CairoSurfaceSetDeviceScalePtr) (cairo_surface_t*,double,double) =
+        (void (*)(cairo_surface_t*,double,double)) dlsym(RTLD_DEFAULT,
+        "cairo_surface_set_device_scale");
+
         if (cr) {
             cairo_surface_t *surf = cairo_get_target(cr);
+            if (GdkScaleFactor() > 1) {
+                // Disable auto-scaling on HiDPI devices, let mozilla manage it.
+                (*CairoSurfaceSetDeviceScalePtr)(surf, 1, 1);
+            }
             if (cairo_surface_status(surf) != CAIRO_STATUS_SUCCESS) {
               NS_NOTREACHED("Missing cairo target?");
               return nullptr;
             }
             mThebesSurface = gfxASurface::Wrap(surf);
         } else
 #endif
 #endif // (MOZ_WIDGET_GTK == 3)
@@ -6286,16 +6319,18 @@ nsWindow::BeginMoveDrag(WidgetMouseEvent
 
     GdkWindow *gdk_window;
     gint button, screenX, screenY;
     if (!GetDragInfo(aEvent, &gdk_window, &button, &screenX, &screenY)) {
         return NS_ERROR_FAILURE;
     }
 
     // tell the window manager to start the move
+    screenX = DevicePixelsToGdkCoordRoundDown(screenX);
+    screenY = DevicePixelsToGdkCoordRoundDown(screenY);
     gdk_window_begin_move_drag(gdk_window, button, screenX, screenY,
                                aEvent->time);
 
     return NS_OK;
 }
 
 NS_IMETHODIMP
 nsWindow::BeginResizeDrag(WidgetGUIEvent* aEvent,
@@ -6377,16 +6412,80 @@ nsWindow::ClearCachedResources()
     for (GList* list = children; list; list = list->next) {
         nsWindow* window = get_window_for_gdk_window(GDK_WINDOW(list->data));
         if (window) {
             window->ClearCachedResources();
         }
     }
 }
 
+gint
+nsWindow::GdkScaleFactor()
+{
+#if (MOZ_WIDGET_GTK >= 3)
+    // Available as of GTK 3.10+
+    static gint (*GdkWindowGetScaleFactorPtr) (GdkWindow*) =
+        (gint (*)(GdkWindow*)) dlsym(RTLD_DEFAULT,
+        "gdk_window_get_scale_factor");
+    if (GdkWindowGetScaleFactorPtr)
+        return (*GdkWindowGetScaleFactorPtr)(mGdkWindow);
+#endif
+    return 1;
+}
+
+
+gint
+nsWindow::DevicePixelsToGdkCoordRoundUp(int pixels) {
+    return NSToIntCeil(float(pixels)/float(GdkScaleFactor()));
+}
+
+gint
+nsWindow::DevicePixelsToGdkCoordRoundDown(int pixels) {
+    return NSToIntFloor(float(pixels)/float(GdkScaleFactor()));
+}
+
+GdkPoint
+nsWindow::DevicePixelsToGdkPointRoundDown(nsIntPoint point) {
+    float scale = GdkScaleFactor();
+    return { NSToIntFloor(float(point.x)/scale),
+             NSToIntFloor(float(point.y)/scale) };
+}
+
+GdkRectangle
+nsWindow::DevicePixelsToGdkRectRoundOut(nsIntRect rect) {
+    gint scale = GdkScaleFactor();
+    nsIntRect scaledRect = rect;
+    scaledRect.ScaleInverseRoundOut(scale);
+    return { scaledRect.x,
+             scaledRect.y,
+             scaledRect.width,
+             scaledRect.height };
+}
+
+int
+nsWindow::GdkCoordToDevicePixels(gint coords) {
+    return coords * GdkScaleFactor();
+}
+
+nsIntPoint
+nsWindow::GdkPointToDevicePixels(GdkPoint point) {
+    gint scale = GdkScaleFactor();
+    return nsIntPoint(point.x * scale,
+                      point.y * scale);
+}
+
+nsIntRect
+nsWindow::GdkRectToDevicePixels(GdkRectangle rect) {
+    gint scale = GdkScaleFactor();
+    return nsIntRect(rect.x * scale,
+                     rect.y * scale,
+                     rect.width * scale,
+                     rect.height * scale);
+}
+
 nsresult
 nsWindow::SynthesizeNativeMouseEvent(nsIntPoint aPoint,
                                      uint32_t aNativeMessage,
                                      uint32_t aModifierFlags)
 {
   if (!mGdkWindow) {
     return NS_OK;
   }
diff --git a/widget/gtk/nsWindow.h b/widget/gtk/nsWindow.h
--- a/widget/gtk/nsWindow.h
+++ b/widget/gtk/nsWindow.h
@@ -92,16 +92,17 @@ public:
     NS_IMETHOD         Create(nsIWidget        *aParent,
                               nsNativeWidget   aNativeParent,
                               const nsIntRect  &aRect,
                               nsDeviceContext *aContext,
                               nsWidgetInitData *aInitData);
     NS_IMETHOD         Destroy(void);
     virtual nsIWidget *GetParent();
     virtual float      GetDPI();
+    virtual double     GetDefaultScaleInternal();
     virtual nsresult   SetParent(nsIWidget* aNewParent);
     NS_IMETHOD         SetModal(bool aModal);
     virtual bool       IsVisible() const;
     NS_IMETHOD         ConstrainPosition(bool aAllowSlop,
                                          int32_t *aX,
                                          int32_t *aY);
     virtual void       SetSizeConstraints(const SizeConstraints& aConstraints);
     NS_IMETHOD         Move(double aX,
@@ -468,16 +469,30 @@ private:
      * The instance is created when the top level widget is created.  And when
      * the widget is destroyed, it's released.  All child windows refer its
      * ancestor widget's instance.  So, one set of IM contexts is created for
      * all windows in a hierarchy.  If the children are released after the top
      * level window is released, the children still have a valid pointer,
      * however, IME doesn't work at that time.
      */
     nsRefPtr<nsGtkIMModule> mIMModule;
+
+    // HiDPI scale conversion
+    gint GdkScaleFactor();
+
+    // To GDK
+    gint DevicePixelsToGdkCoordRoundUp(int pixels);
+    gint DevicePixelsToGdkCoordRoundDown(int pixels);
+    GdkPoint DevicePixelsToGdkPointRoundDown(nsIntPoint point);
+    GdkRectangle DevicePixelsToGdkRectRoundOut(nsIntRect rect);
+
+    // From GDK
+    int GdkCoordToDevicePixels(gint coords);
+    nsIntPoint GdkPointToDevicePixels(GdkPoint point);
+    nsIntRect GdkRectToDevicePixels(GdkRectangle rect);
 };
 
 class nsChildWindow : public nsWindow {
 public:
     nsChildWindow();
     ~nsChildWindow();
 };