st/viewport: Add clip-to-view property

This property controls whether the viewport clips the content to its own
allocation or not. This will be necessary in special modes that we want to
render past the viewport inside a scrollview.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1630>

src/st/st-viewport.c

@@ -55,6 +55,7 @@ static void st_viewport_scrollable_interface_init (StScrollableInterface *iface)
 
 enum {
   PROP_0,
+  PROP_CLIP_TO_VIEW,
   PROP_HADJUST,
   PROP_VADJUST
 };
@@ -63,6 +64,7 @@ typedef struct
 {
   StAdjustment *hadjustment;
   StAdjustment *vadjustment;
+  gboolean clip_to_view;
 } StViewportPrivate;
 
 G_DEFINE_TYPE_WITH_CODE (StViewport, st_viewport, ST_TYPE_WIDGET,
@@ -163,12 +165,28 @@ st_viewport_scrollable_interface_init (StScrollableInterface *iface)
   iface->get_adjustments = scrollable_get_adjustments;
 }
 
+static void
+st_viewport_set_clip_to_view (StViewport *viewport,
+                              gboolean    clip_to_view)
+{
+  StViewportPrivate *priv =
+    st_viewport_get_instance_private (viewport);
+
+  if (!!priv->clip_to_view != !!clip_to_view)
+    {
+      priv->clip_to_view = clip_to_view;
+      clutter_actor_queue_redraw (CLUTTER_ACTOR (viewport));
+    }
+}
+
 static void
 st_viewport_get_property (GObject    *object,
                           guint       property_id,
                           GValue     *value,
                           GParamSpec *pspec)
 {
+  StViewportPrivate *priv =
+    st_viewport_get_instance_private (ST_VIEWPORT (object));
   StAdjustment *adjustment;
 
   switch (property_id)
@@ -183,6 +201,10 @@ st_viewport_get_property (GObject    *object,
       g_value_set_object (value, adjustment);
       break;
 
+    case PROP_CLIP_TO_VIEW:
+      g_value_set_boolean (value, priv->clip_to_view);
+      break;
+
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
     }
@@ -212,6 +234,10 @@ st_viewport_set_property (GObject      *object,
                                   g_value_get_object (value));
       break;
 
+    case PROP_CLIP_TO_VIEW:
+      st_viewport_set_clip_to_view (viewport, g_value_get_boolean (value));
+      break;
+
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
     }
@@ -405,7 +431,7 @@ st_viewport_paint (ClutterActor        *actor,
   /* The content area forms the viewport into the scrolled contents, while
    * the borders and background stay in place; after drawing the borders and
    * background, we clip to the content area */
-  if (priv->hadjustment || priv->vadjustment)
+  if (priv->clip_to_view && (priv->hadjustment || priv->vadjustment))
     {
       cogl_framebuffer_push_rectangle_clip (fb,
                                             (int)content_box.x1,
@@ -419,7 +445,7 @@ st_viewport_paint (ClutterActor        *actor,
        child = clutter_actor_get_next_sibling (child))
     clutter_actor_paint (child, paint_context);
 
-  if (priv->hadjustment || priv->vadjustment)
+  if (priv->clip_to_view && (priv->hadjustment || priv->vadjustment))
     cogl_framebuffer_pop_clip (fb);
 }
 
@@ -478,6 +504,9 @@ st_viewport_get_paint_volume (ClutterActor       *actor,
   if (!clutter_actor_has_allocation (actor))
     return FALSE;
 
+  if (!priv->clip_to_view)
+    return CLUTTER_ACTOR_CLASS (st_viewport_parent_class)->get_paint_volume (actor, volume);
+
   /* When have an adjustment we are clipped to the content box, so base
    * our paint volume on that. */
   if (priv->hadjustment || priv->vadjustment)
@@ -558,6 +587,14 @@ st_viewport_class_init (StViewportClass *klass)
   actor_class->get_paint_volume = st_viewport_get_paint_volume;
   actor_class->pick = st_viewport_pick;
 
+  g_object_class_install_property (object_class,
+                                   PROP_CLIP_TO_VIEW,
+                                   g_param_spec_boolean ("clip-to-view",
+                                                         "Clip to view",
+                                                         "Clip to view",
+                                                         TRUE,
+                                                         ST_PARAM_READWRITE));
+
   /* StScrollable properties */
   g_object_class_override_property (object_class,
                                     PROP_HADJUST,
@@ -566,10 +603,13 @@ st_viewport_class_init (StViewportClass *klass)
   g_object_class_override_property (object_class,
                                     PROP_VADJUST,
                                     "vadjustment");
-
 }
 
 static void
 st_viewport_init (StViewport *self)
 {
+  StViewportPrivate *priv =
+    st_viewport_get_instance_private (self);
+
+  priv->clip_to_view = TRUE;
 }