[gtk/wip/otte/gleanup: 35/59] gdk: Allow GdkDrawContext with a %NULL surface

[Chun-wei Fan <fanchunwei src gnome org>]

commit 906f4cb3c794d2fb2cc322d01952251bb87fed47
Author: Benjamin Otte <otte redhat com>
Date:   Sun Jul 4 02:43:49 2021 +0200

    gdk: Allow GdkDrawContext with a %NULL surface
    
    This is not used yet, but it allows surfaceless GL contexts.
    
    For that purpose, we need to make the display a construct-only property,
    so that it can be set when the surface isn't.
    
    This adds a bunch of very picky checks in the constructor so nothing bad
    can happen.

 gdk/gdkdrawcontext.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)
---
diff --git a/gdk/gdkdrawcontext.c b/gdk/gdkdrawcontext.c
index d377c227a2..d1c5cd0960 100644
--- a/gdk/gdkdrawcontext.c
+++ b/gdk/gdkdrawcontext.c
@@ -43,6 +43,7 @@
 typedef struct _GdkDrawContextPrivate GdkDrawContextPrivate;
 
 struct _GdkDrawContextPrivate {
+  GdkDisplay *display;
   GdkSurface *surface;
 
   cairo_region_t *frame_region;
@@ -77,6 +78,7 @@ gdk_draw_context_dispose (GObject *gobject)
       priv->surface->draw_contexts = g_slist_remove (priv->surface->draw_contexts, context);
       g_clear_object (&priv->surface);
     }
+  g_clear_object (&priv->display);
 
   G_OBJECT_CLASS (gdk_draw_context_parent_class)->dispose (gobject);
 }
@@ -92,10 +94,31 @@ gdk_draw_context_set_property (GObject      *gobject,
 
   switch (prop_id)
     {
+    case PROP_DISPLAY:
+      if (priv->display != NULL)
+        {
+          g_assert (g_value_get_object (value) == NULL);
+        }
+      else
+        {
+          priv->display = g_value_dup_object (value);
+        }
+      break;
+
     case PROP_SURFACE:
       priv->surface = g_value_dup_object (value);
-      g_assert (priv->surface != NULL);
-      priv->surface->draw_contexts = g_slist_prepend (priv->surface->draw_contexts, context);
+      if (priv->surface)
+        {
+          priv->surface->draw_contexts = g_slist_prepend (priv->surface->draw_contexts, context);
+          if (priv->display)
+            {
+              g_assert (priv->display == gdk_surface_get_display (priv->surface));
+            }
+          else
+            {
+              priv->display = g_object_ref (gdk_surface_get_display (priv->surface));
+            }
+        }
       break;
 
     default:
@@ -148,7 +171,8 @@ gdk_draw_context_class_init (GdkDrawContextClass *klass)
                          P_("Display"),
                          P_("The GDK display used to create the context"),
                          GDK_TYPE_DISPLAY,
-                         G_PARAM_READABLE |
+                         G_PARAM_READWRITE |
+                         G_PARAM_CONSTRUCT_ONLY |
                          G_PARAM_STATIC_STRINGS);
 
   /**
@@ -228,7 +252,7 @@ gdk_draw_context_get_display (GdkDrawContext *context)
 
   g_return_val_if_fail (GDK_IS_DRAW_CONTEXT (context), NULL);
 
-  return priv->surface ? gdk_surface_get_display (priv->surface) : NULL;
+  return priv->display;
 }
 
 /**