[gtk+] quartz: fix pixelated image surfaces in retina/hidpi mode

[Christoph Reiter <creiter src gnome org>]

commit 3f077ec36f4a59e803c9f4509996269c862e04af
Author: Christoph Reiter <creiter src gnome org>
Date:   Wed Mar 16 19:25:30 2016 +0100

    quartz: fix pixelated image surfaces in retina/hidpi mode
    
    gtk+ currently depends on the scaling factor and the cairo device scale
    of both the backend surfaces and image surfaces to be equal.
    
    Until now we didn't apply a cairo device scale at all and depended on the
    automatic scaling of CGContexts. This works when drawing with cairo but
    fails in case of image surfaces, which get requested at a too small size.
    
    To make the quartz backend behave more like the X11 one, set the cairo device
    scale on the surface in gdk_quartz_ref_cairo_surface(). As this conflicts
    with the default scaling done by CGContext (we would get double scaling)
    undo the CGContext scaling using CGContextScaleCTM().
    
    This patch is based on the following patches by Brion Vibber:
        https://bugzilla.gnome.org/show_bug.cgi?id=740199#c4
        https://bugs.freedesktop.org/show_bug.cgi?id=69796#c4
    
    https://bugzilla.gnome.org/show_bug.cgi?id=763779

 gdk/quartz/gdkwindow-quartz.c |   15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)
---
diff --git a/gdk/quartz/gdkwindow-quartz.c b/gdk/quartz/gdkwindow-quartz.c
index 62710a2..f3eceb1 100644
--- a/gdk/quartz/gdkwindow-quartz.c
+++ b/gdk/quartz/gdkwindow-quartz.c
@@ -121,6 +121,7 @@ gdk_window_impl_quartz_get_context (GdkWindowImplQuartz *window_impl,
                                    gboolean             antialias)
 {
   CGContextRef cg_context;
+  CGSize scale;
 
   if (GDK_WINDOW_DESTROYED (window_impl->wrapper))
     return NULL;
@@ -141,6 +142,12 @@ gdk_window_impl_quartz_get_context (GdkWindowImplQuartz *window_impl,
   CGContextSaveGState (cg_context);
   CGContextSetAllowsAntialiasing (cg_context, antialias);
 
+  /* Undo the default scaling transform, since we apply our own
+   * in gdk_quartz_ref_cairo_surface () */
+  scale = CGContextConvertSizeToDeviceSpace (cg_context,
+                                             CGSizeMake (1.0, 1.0));
+  CGContextScaleCTM (cg_context, 1.0 / scale.width, 1.0 / scale.height);
+
   return cg_context;
 }
 
@@ -317,10 +324,14 @@ gdk_quartz_ref_cairo_surface (GdkWindow *window)
 
   if (!impl->cairo_surface)
     {
+      gint scale = gdk_window_get_scale_factor (impl->wrapper);
+
       impl->cairo_surface = 
           gdk_quartz_create_cairo_surface (impl,
-                                           gdk_window_get_width (impl->wrapper),
-                                           gdk_window_get_height (impl->wrapper));
+                                           gdk_window_get_width (impl->wrapper) * scale,
+                                           gdk_window_get_height (impl->wrapper) * scale);
+
+      cairo_surface_set_device_scale (impl->cairo_surface, scale, scale);
     }
   else
     cairo_surface_reference (impl->cairo_surface);