Associate the drawing context to the Cairo context

Instead of associating the GdkWindow that created the GdkDrawingContext
we can directly bind the Cairo context to the GDK drawing context.

Cairo contexts created via gdk_cairo_create() go back to not having a
GdkWindow associated to them, like they did before we introduced the
gdk_window_begin_draw_frame() API.

https://bugzilla.gnome.org/show_bug.cgi?id=766675

docs/reference/gdk/gdk3-sections.txt

@@ -625,7 +625,7 @@ gdk_window_create_similar_surface
 gdk_window_create_similar_image_surface
 gdk_cairo_create
 gdk_cairo_get_clip_rectangle
-gdk_cairo_get_window
+gdk_cairo_get_drawing_context
 gdk_cairo_set_source_color
 gdk_cairo_set_source_rgba
 gdk_cairo_set_source_pixbuf

gdk/gdkcairo.h

@@ -25,6 +25,7 @@
 #include <gdk/gdkversionmacros.h>
 #include <gdk/deprecated/gdkcolor.h>
 #include <gdk/gdkrgba.h>
+#include <gdk/gdkdrawingcontext.h>
 #include <gdk/gdkpixbuf.h>
 #include <pango/pangocairo.h>
 
@@ -32,8 +33,7 @@ G_BEGIN_DECLS
 
 GDK_AVAILABLE_IN_ALL
 cairo_t  * gdk_cairo_create             (GdkWindow          *window);
-GDK_AVAILABLE_IN_3_22
+
-GdkWindow * gdk_cairo_get_window        (cairo_t            *cr);
 GDK_AVAILABLE_IN_ALL
 gboolean   gdk_cairo_get_clip_rectangle (cairo_t            *cr,
                                          GdkRectangle       *rect);
@@ -83,6 +83,8 @@ void       gdk_cairo_draw_from_gl (cairo_t              *cr,
                                    int                   width,
                                    int                   height);
 
+GDK_AVAILABLE_IN_3_22
+GdkDrawingContext *     gdk_cairo_get_drawing_context   (cairo_t *cr);
 
 G_END_DECLS
 

gdk/gdkdrawingcontext.c

@@ -178,6 +178,34 @@ gdk_drawing_context_init (GdkDrawingContext *self)
 {
 }
 
+static const cairo_user_data_key_t draw_context_key;
+
+static void
+gdk_cairo_set_drawing_context (cairo_t           *cr,
+                               GdkDrawingContext *context)
+{
+  cairo_set_user_data (cr, &draw_context_key, context, NULL);
+}
+
+/**
+ * gdk_cairo_get_drawing_context:
+ * @cr: a Cairo context
+ *
+ * Retrieves the #GdkDrawingContext that created the Cairo
+ * context @cr.
+ *
+ * Returns: (transfer none) (nullable): a #GdkDrawingContext, if any is set
+ *
+ * Since: 3.22
+ */
+GdkDrawingContext *
+gdk_cairo_get_drawing_context (cairo_t *cr)
+{
+  g_return_val_if_fail (cr != NULL, NULL);
+
+  return cairo_get_user_data (cr, &draw_context_key);
+}
+
 /**
  * gdk_drawing_context_get_cairo_context:
  * @context:
@@ -204,6 +232,9 @@ gdk_drawing_context_get_cairo_context (GdkDrawingContext *context)
   if (context->cr == NULL)
     {
       context->cr = gdk_cairo_create (context->window);
+
+      gdk_cairo_set_drawing_context (context->cr, context);
+
       gdk_cairo_region (context->cr, context->clip);
       cairo_clip (context->cr);
     }

gdk/gdkwindow.c

@@ -3111,33 +3111,6 @@ gdk_window_begin_paint_region (GdkWindow            *window,
   gdk_window_begin_paint_internal (window, region);
 }
 
-static const cairo_user_data_key_t draw_context_window_key;
-
-static void
-gdk_cairo_set_window (cairo_t *cr,
-                      GdkWindow *window)
-{
-  cairo_set_user_data (cr, &draw_context_window_key, window, NULL);
-}
-
-/**
- * gdk_cairo_get_window:
- * @cr: a Cairo context created by gdk_window_begin_draw_frame()
- *
- * Retrieves the #GdkWindow that created the Cairo context @cr.
- *
- * Returns: (nullable) (transfer none): a #GdkWindow
- *
- * Since: 3.22
- */
-GdkWindow *
-gdk_cairo_get_window (cairo_t *cr)
-{
-  g_return_val_if_fail (cr != NULL, NULL);
-
-  return cairo_get_user_data (cr, &draw_context_window_key);
-}
-
 /**
  * gdk_window_begin_draw_frame:
  * @window: a #GdkWindow
@@ -3541,8 +3514,6 @@ gdk_cairo_create (GdkWindow *window)
 
   cr = cairo_create (surface);
 
-  gdk_cairo_set_window (cr, window);
-
   if (window->impl_window->current_paint.region != NULL)
     {
       region = cairo_region_copy (window->impl_window->current_paint.region);

gtk/gtkwidget.c

@@ -6925,6 +6925,7 @@ gboolean
 gtk_cairo_should_draw_window (cairo_t   *cr,
                               GdkWindow *window)
 {
+  GdkDrawingContext *context;
   GdkWindow *tmp;
 
   g_return_val_if_fail (cr != NULL, FALSE);
@@ -6933,8 +6934,11 @@ gtk_cairo_should_draw_window (cairo_t   *cr,
   if (gtk_cairo_is_marked_for_draw (cr))
     return TRUE;
 
-  tmp = gdk_cairo_get_window (cr);
+  context = gdk_cairo_get_drawing_context (cr);
+  if (context == NULL)
+    return TRUE;
 
+  tmp = gdk_drawing_context_get_window (context);
   if (tmp == NULL)
     return TRUE;
 
@@ -6964,22 +6968,25 @@ gtk_widget_draw_internal (GtkWidget *widget,
 
   if (gdk_cairo_get_clip_rectangle (cr, NULL))
     {
-      GdkWindow *event_window;
+      GdkWindow *event_window = NULL;
       gboolean result;
       gboolean push_group;
 
       /* If this was a cairo_t passed via gtk_widget_draw() then we don't
-       * require a window
+       * require a window; otherwise we check for the window associated
+       * to the drawing context and mark it using the clip region of the
+       * Cairo context.
        */
-      if (gtk_cairo_is_marked_for_draw (cr))
+      if (!gtk_cairo_is_marked_for_draw (cr))
         {
-          event_window = NULL;
+          GdkDrawingContext *context = gdk_cairo_get_drawing_context (cr);
-        }
+
-      else
+          if (context != NULL)
-        {
+            {
-          event_window = gdk_cairo_get_window (cr);
+              event_window = gdk_drawing_context_get_window (context);
-          if (event_window != NULL)
+              if (event_window != NULL)
-            gdk_window_mark_paint_from_clip (event_window, cr);
+                gdk_window_mark_paint_from_clip (event_window, cr);
+            }
         }
 
       push_group =