[mutter] theme, frames: Use surface device scale instead of cairo_scale

[Jonas Ådahl <jadahl src gnome org>]

commit 4339b23dd08b2bb7de8a6f01b176c40c6fca082f
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Fri Mar 30 13:57:50 2018 -0500

    theme, frames: Use surface device scale instead of cairo_scale
    
    Gtk now is caching the themed cairo surfaces, then as per
    commit gtk@e36b629c the surface device scale is used to figure
    out the current paint scaling.
    
    Without this when using background-image's for window buttons
    the -gtk-scaled icons isn't properly resized.
    
    Fixes #99

 src/ui/frames.c | 12 ++++++++++--
 src/ui/theme.c  | 14 ++++++++++++--
 2 files changed, 22 insertions(+), 4 deletions(-)
---
diff --git a/src/ui/frames.c b/src/ui/frames.c
index 129a9e59b..ef7e7df26 100644
--- a/src/ui/frames.c
+++ b/src/ui/frames.c
@@ -1330,7 +1330,9 @@ meta_ui_frame_get_mask (MetaUIFrame *frame,
   MetaFrameBorders borders;
   MetaFrameFlags flags;
   MetaRectangle frame_rect;
-  int scale = meta_theme_get_window_scaling_factor ();
+  cairo_surface_t *surface;
+  double xscale, yscale;
+  int scale;
 
   meta_window_get_frame_rect (frame->meta_window, &frame_rect);
 
@@ -1340,7 +1342,11 @@ meta_ui_frame_get_mask (MetaUIFrame *frame,
   meta_ui_frame_get_borders (frame, &borders);
 
   /* See comment in meta_frame_layout_draw_with_style() for details on HiDPI handling */
-  cairo_scale (cr, scale, scale);
+  scale = meta_theme_get_window_scaling_factor ();
+  surface = cairo_get_target (cr);
+  cairo_surface_get_device_scale (surface, &xscale, &yscale);
+  cairo_surface_set_device_scale (surface, scale, scale);
+
   gtk_render_background (frame->style_info->styles[META_STYLE_ELEMENT_FRAME], cr,
                          borders.invisible.left / scale,
                          borders.invisible.top / scale,
@@ -1349,6 +1355,8 @@ meta_ui_frame_get_mask (MetaUIFrame *frame,
                          borders.invisible.left / scale,
                          borders.invisible.top / scale,
                          frame_rect.width / scale, borders.total.top / scale);
+
+  cairo_surface_set_device_scale (surface, xscale, yscale);
 }
 
 /* XXX -- this is disgusting. Find a better approach here.
diff --git a/src/ui/theme.c b/src/ui/theme.c
index b909d9b6a..c0bb9b66a 100644
--- a/src/ui/theme.c
+++ b/src/ui/theme.c
@@ -736,7 +736,9 @@ meta_frame_layout_draw_with_style (MetaFrameLayout         *layout,
   GdkRectangle titlebar_rect;
   GdkRectangle button_rect;
   const MetaFrameBorders *borders;
-  int scale = meta_theme_get_window_scaling_factor ();
+  cairo_surface_t *frame_surface;
+  double xscale, yscale;
+  int scale;
 
   /* We opt out of GTK+/Clutter's HiDPI handling, so we have to do the scaling
    * ourselves; the nitty-gritty is a bit confusing, so here is an overview:
@@ -748,8 +750,14 @@ meta_frame_layout_draw_with_style (MetaFrameLayout         *layout,
    *  - for drawing, we scale the canvas to have GTK+ render elements (borders,
    *    radii, ...) at the correct scale - as a result, we have to "unscale"
    *    the geometry again to not apply the scaling twice
+   *  - As per commit e36b629c GTK expects the device scale to be set and match
+   *    the final scaling or the surface caching won't take this in account
+   *    breaking -gtk-scaled items.
    */
-  cairo_scale (cr, scale, scale);
+  scale = meta_theme_get_window_scaling_factor ();
+  frame_surface = cairo_get_target (cr);
+  cairo_surface_get_device_scale (frame_surface, &xscale, &yscale);
+  cairo_surface_set_device_scale (frame_surface, scale, scale);
 
   borders = &fgeom->borders;
 
@@ -905,6 +913,8 @@ meta_frame_layout_draw_with_style (MetaFrameLayout         *layout,
         gtk_style_context_remove_class (style, button_class);
       gtk_style_context_set_state (style, state);
     }
+
+  cairo_surface_set_device_scale (frame_surface, xscale, yscale);
 }
 
 /**