[gimp/gtk3-port: 228/229] libgimpwidgets: Separate ruler text layer from background.

[Michael Natterer <mitch src gnome org>]

commit cd6a1976023a7e6278b7ce128744e9e63ed4a22b
Author: Michael Henning <drawoc darkrefraction com>
Date:   Mon Sep 28 22:42:46 2015 -0400

    libgimpwidgets: Separate ruler text layer from background.
    
    Also fix failing to clear backing_store at the same time.

 libgimpwidgets/gimpruler.c |   17 ++++++++++++-----
 1 files changed, 12 insertions(+), 5 deletions(-)
---
diff --git a/libgimpwidgets/gimpruler.c b/libgimpwidgets/gimpruler.c
index 4938927..51f8df4 100644
--- a/libgimpwidgets/gimpruler.c
+++ b/libgimpwidgets/gimpruler.c
@@ -970,8 +970,14 @@ static gboolean
 gimp_ruler_draw (GtkWidget *widget,
                  cairo_t   *cr)
 {
-  GimpRuler        *ruler = GIMP_RULER (widget);
-  GimpRulerPrivate *priv  = GIMP_RULER_GET_PRIVATE (ruler);
+  GimpRuler        *ruler   = GIMP_RULER (widget);
+  GimpRulerPrivate *priv    = GIMP_RULER_GET_PRIVATE (ruler);
+  GtkStyleContext  *context = gtk_widget_get_style_context (widget);
+  GtkAllocation     allocation;
+
+  gtk_widget_get_allocation (widget, &allocation);
+  gtk_render_background (context, cr, 0, 0, allocation.width, allocation.height);
+  gtk_render_frame (context, cr, 0, 0, allocation.width, allocation.height);
 
   if (! priv->backing_store_valid)
     gimp_ruler_draw_ticks (ruler);
@@ -1036,8 +1042,9 @@ gimp_ruler_draw_ticks (GimpRuler *ruler)
 
   cr = cairo_create (priv->backing_store);
 
-  gtk_render_background (context, cr, 0, 0, allocation.width, allocation.height);
-  gtk_render_frame (context, cr, 0, 0, allocation.width, allocation.height);
+  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
+  cairo_paint (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
 
   gtk_style_context_get_color (context, gtk_widget_get_state_flags (widget),
                                &color);
@@ -1348,7 +1355,7 @@ gimp_ruler_make_pixmap (GimpRuler *ruler)
 
   priv->backing_store =
     gdk_window_create_similar_surface (gtk_widget_get_window (widget),
-                                       CAIRO_CONTENT_COLOR,
+                                       CAIRO_CONTENT_COLOR_ALPHA,
                                        allocation.width,
                                        allocation.height);