Fixed Timestep Interpolation (2D)

Adds fixed timestep interpolation to the rendering server (2D only).
Switchable on and off with a project setting (default is off).

Co-authored-by: lawnjelly <lawnjelly@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/scene/main/canvas_item.cpp b/scene/main/canvas_item.cpp
index 2d0da075ba..768c83954b 100644
--- a/scene/main/canvas_item.cpp
+++ b/scene/main/canvas_item.cpp
@@ -336,6 +336,19 @@ void CanvasItem::_notification(int p_what) {
 				get_parent()->connect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::canvas_parent_mark_dirty).bind(get_parent()), CONNECT_REFERENCE_COUNTED);
 			}
 
+			// If using physics interpolation, reset for this node only,
+			// as a helper, as in most cases, users will want items reset when
+			// adding to the tree.
+			// In cases where they move immediately after adding,
+			// there will be little cost in having two resets as these are cheap,
+			// and it is worth it for convenience.
+			// Do not propagate to children, as each child of an added branch
+			// receives its own NOTIFICATION_ENTER_TREE, and this would
+			// cause unnecessary duplicate resets.
+			if (is_physics_interpolated_and_enabled()) {
+				notification(NOTIFICATION_RESET_PHYSICS_INTERPOLATION);
+			}
+
 		} break;
 		case NOTIFICATION_EXIT_TREE: {
 			ERR_MAIN_THREAD_GUARD;
@@ -360,6 +373,12 @@ void CanvasItem::_notification(int p_what) {
 			}
 		} break;
 
+		case NOTIFICATION_RESET_PHYSICS_INTERPOLATION: {
+			if (is_visible_in_tree() && is_physics_interpolated()) {
+				RenderingServer::get_singleton()->canvas_item_reset_physics_interpolation(canvas_item);
+			}
+		} break;
+
 		case NOTIFICATION_VISIBILITY_CHANGED: {
 			ERR_MAIN_THREAD_GUARD;
 
@@ -921,6 +940,10 @@ void CanvasItem::_notify_transform(CanvasItem *p_node) {
 	}
 }
 
+void CanvasItem::_physics_interpolated_changed() {
+	RenderingServer::get_singleton()->canvas_item_set_interpolated(canvas_item, is_physics_interpolated());
+}
+
 Rect2 CanvasItem::get_viewport_rect() const {
 	ERR_READ_THREAD_GUARD_V(Rect2());
 	ERR_FAIL_COND_V(!is_inside_tree(), Rect2());