2D Fixed Timestep Interpolation

Adds support to canvas items and Camera2D.

core/math/transform_interpolator.cpp

@@ -30,6 +30,51 @@
 
 #include "transform_interpolator.h"
 
+#include "core/math/transform_2d.h"
+
+void TransformInterpolator::interpolate_transform2D(const Transform2D &p_prev, const Transform2D &p_curr, Transform2D &r_result, real_t p_fraction) {
+	//extract parameters
+	Vector2 p1 = p_prev.get_origin();
+	Vector2 p2 = p_curr.get_origin();
+
+	// Special case for physics interpolation, if flipping, don't interpolate basis.
+	// If the determinant polarity changes, the handedness of the coordinate system changes.
+	if (_sign(p_prev.basis_determinant()) != _sign(p_curr.basis_determinant())) {
+		r_result.elements[0] = p_curr.elements[0];
+		r_result.elements[1] = p_curr.elements[1];
+		r_result.set_origin(Vector2::linear_interpolate(p1, p2, p_fraction));
+		return;
+	}
+
+	real_t r1 = p_prev.get_rotation();
+	real_t r2 = p_curr.get_rotation();
+
+	Size2 s1 = p_prev.get_scale();
+	Size2 s2 = p_curr.get_scale();
+
+	//slerp rotation
+	Vector2 v1(Math::cos(r1), Math::sin(r1));
+	Vector2 v2(Math::cos(r2), Math::sin(r2));
+
+	real_t dot = v1.dot(v2);
+
+	dot = CLAMP(dot, -1, 1);
+
+	Vector2 v;
+
+	if (dot > 0.9995f) {
+		v = Vector2::linear_interpolate(v1, v2, p_fraction).normalized(); //linearly interpolate to avoid numerical precision issues
+	} else {
+		real_t angle = p_fraction * Math::acos(dot);
+		Vector2 v3 = (v2 - v1 * dot).normalized();
+		v = v1 * Math::cos(angle) + v3 * Math::sin(angle);
+	}
+
+	//construct matrix
+	r_result = Transform2D(Math::atan2(v.y, v.x), Vector2::linear_interpolate(p1, p2, p_fraction));
+	r_result.scale_basis(Vector2::linear_interpolate(s1, s2, p_fraction));
+}
+
 void TransformInterpolator::interpolate_transform(const Transform &p_prev, const Transform &p_curr, Transform &r_result, real_t p_fraction) {
 	r_result.origin = p_prev.origin + ((p_curr.origin - p_prev.origin) * p_fraction);
 	interpolate_basis(p_prev.basis, p_curr.basis, r_result.basis, p_fraction);

core/math/transform_interpolator.h

@@ -46,7 +46,7 @@
 // several frames may occur between each physics tick, which will make it cheaper
 // than performing every frame.
 
-class Transform;
+struct Transform2D;
 
 class TransformInterpolator {
 public:
@@ -66,6 +66,7 @@ class TransformInterpolator {
 	static Quat _basis_to_quat_unchecked(const Basis &p_basis);
 	static bool _basis_is_orthogonal(const Basis &p_basis, real_t p_epsilon = 0.01f);
 	static bool _basis_is_orthogonal_any_scale(const Basis &p_basis);
+	static bool _sign(real_t p_val) { return p_val >= 0; }
 
 	static void interpolate_basis_linear(const Basis &p_prev, const Basis &p_curr, Basis &r_result, real_t p_fraction);
 	static void interpolate_basis_scaled_slerp(Basis p_prev, Basis p_curr, Basis &r_result, real_t p_fraction);
@@ -75,6 +76,7 @@ class TransformInterpolator {
 	// These will be slower.
 	static void interpolate_transform(const Transform &p_prev, const Transform &p_curr, Transform &r_result, real_t p_fraction);
 	static void interpolate_basis(const Basis &p_prev, const Basis &p_curr, Basis &r_result, real_t p_fraction);
+	static void interpolate_transform2D(const Transform2D &p_prev, const Transform2D &p_curr, Transform2D &r_result, real_t p_fraction);
 
 	// Optimized function when you know ahead of time the method
 	static void interpolate_transform_via_method(const Transform &p_prev, const Transform &p_curr, Transform &r_result, real_t p_fraction, Method p_method);

core/os/main_loop.h

@@ -67,6 +67,7 @@ class MainLoop : public Object {
 	virtual void input_text(const String &p_text);
 
 	virtual void init();
+	virtual void iteration_prepare() {}
 	virtual bool iteration(float p_time);
 	virtual void iteration_end() {}
 	virtual bool idle(float p_time);

doc/classes/Control.xml

@@ -825,6 +825,7 @@
 		<member name="mouse_filter" type="int" setter="set_mouse_filter" getter="get_mouse_filter" enum="Control.MouseFilter" default="0">
 			Controls whether the control will be able to receive mouse button input events through [method _gui_input] and how these events should be handled. Also controls whether the control can receive the [signal mouse_entered], and [signal mouse_exited] signals. See the constants to learn what each does.
 		</member>
+		<member name="physics_interpolation_mode" type="int" setter="set_physics_interpolation_mode" getter="get_physics_interpolation_mode" overrides="Node" enum="Node.PhysicsInterpolationMode" default="1" />
 		<member name="rect_clip_content" type="bool" setter="set_clip_contents" getter="is_clipping_contents" default="false">
 			Enables whether rendering of [CanvasItem] based children should be clipped to this control's rectangle. If [code]true[/code], parts of a child which would be visibly outside of this control's rectangle will not be rendered.
 		</member>

doc/classes/VisualServer.xml

@@ -325,6 +325,14 @@
 				Once finished with your RID, you will want to free the RID using the VisualServer's [method free_rid] static method.
 			</description>
 		</method>
+		<method name="canvas_item_reset_physics_interpolation">
+			<return type="void" />
+			<argument index="0" name="item" type="RID" />
+			<description>
+				Prevents physics interpolation for the current physics tick.
+				This is useful when moving a canvas item to a new location, to give an instantaneous change rather than interpolation from the previous location.
+			</description>
+		</method>
 		<method name="canvas_item_set_clip">
 			<return type="void" />
 			<argument index="0" name="item" type="RID" />
@@ -375,6 +383,14 @@
 				Sets the index for the [CanvasItem].
 			</description>
 		</method>
+		<method name="canvas_item_set_interpolated">
+			<return type="void" />
+			<argument index="0" name="item" type="RID" />
+			<argument index="1" name="interpolated" type="bool" />
+			<description>
+				Turns on and off physics interpolation for the canvas item.
+			</description>
+		</method>
 		<method name="canvas_item_set_light_mask">
 			<return type="void" />
 			<argument index="0" name="item" type="RID" />
@@ -463,6 +479,16 @@
 				Sets the [CanvasItem]'s Z index, i.e. its draw order (lower indexes are drawn first).
 			</description>
 		</method>
+		<method name="canvas_item_transform_physics_interpolation">
+			<return type="void" />
+			<argument index="0" name="item" type="RID" />
+			<argument index="1" name="xform" type="Transform2D" />
+			<description>
+				Transforms both the current and previous stored transform for a canvas item.
+				This allows transforming a canvas item without creating a "glitch" in the interpolation.
+				This is particularly useful for large worlds utilising a shifting origin.
+			</description>
+		</method>
 		<method name="canvas_light_attach_to_canvas">
 			<return type="void" />
 			<argument index="0" name="light" type="RID" />

main/main.cpp

@@ -2298,6 +2298,12 @@ bool Main::iteration() {
 
 		PhysicsServer::get_singleton()->flush_queries();
 
+		// Prepare the fixed timestep interpolated nodes
+		// BEFORE they are updated by the physics 2D,
+		// otherwise the current and previous transforms
+		// may be the same, and no interpolation takes place.
+		OS::get_singleton()->get_main_loop()->iteration_prepare();
+
 		Physics2DServer::get_singleton()->sync();
 		Physics2DServer::get_singleton()->flush_queries();
 

scene/2d/camera_2d.cpp

@@ -55,8 +55,12 @@ void Camera2D::_update_scroll() {
 	if (current) {
 		ERR_FAIL_COND(custom_viewport && !ObjectDB::get_instance(custom_viewport_id));
 
-		Transform2D xform = get_camera_transform();
-
+		Transform2D xform;
+		if (is_physics_interpolated_and_enabled()) {
+			xform = _interpolation_data.xform_prev.interpolate_with(_interpolation_data.xform_curr, Engine::get_singleton()->get_physics_interpolation_fraction());
+		} else {
+			xform = get_camera_transform();
+		}
 		viewport->set_canvas_transform(xform);
 
 		Size2 screen_size = viewport->get_visible_rect().size;
@@ -67,13 +71,18 @@ void Camera2D::_update_scroll() {
 }
 
 void Camera2D::_update_process_mode() {
-	// smoothing can be enabled in the editor but will never be active
-	if (process_mode == CAMERA2D_PROCESS_IDLE) {
-		set_process_internal(smoothing_active);
-		set_physics_process_internal(false);
+	if (is_physics_interpolated_and_enabled()) {
+		set_process_internal(is_current());
+		set_physics_process_internal(is_current());
 	} else {
-		set_process_internal(false);
-		set_physics_process_internal(smoothing_active);
+		// smoothing can be enabled in the editor but will never be active
+		if (process_mode == CAMERA2D_PROCESS_IDLE) {
+			set_process_internal(smoothing_active);
+			set_physics_process_internal(false);
+		} else {
+			set_process_internal(false);
+			set_physics_process_internal(smoothing_active);
+		}
 	}
 }
 
@@ -236,13 +245,22 @@ Transform2D Camera2D::get_camera_transform() {
 
 void Camera2D::_notification(int p_what) {
 	switch (p_what) {
-		case NOTIFICATION_INTERNAL_PROCESS:
-		case NOTIFICATION_INTERNAL_PHYSICS_PROCESS: {
+		case NOTIFICATION_INTERNAL_PROCESS: {
 			_update_scroll();
-
+		} break;
+		case NOTIFICATION_INTERNAL_PHYSICS_PROCESS: {
+			if (is_physics_interpolated_and_enabled()) {
+				_interpolation_data.xform_prev = _interpolation_data.xform_curr;
+				_interpolation_data.xform_curr = get_camera_transform();
+			} else {
+				_update_scroll();
+			}
+		} break;
+		case NOTIFICATION_RESET_PHYSICS_INTERPOLATION: {
+			_interpolation_data.xform_prev = _interpolation_data.xform_curr;
 		} break;
 		case NOTIFICATION_TRANSFORM_CHANGED: {
-			if (!smoothing_active) {
+			if (!smoothing_active && !is_physics_interpolated_and_enabled()) {
 				_update_scroll();
 			}
 
@@ -400,10 +418,15 @@ Camera2D::Camera2DProcessMode Camera2D::get_process_mode() const {
 }
 
 void Camera2D::_make_current(Object *p_which) {
+	bool new_current = false;
+
 	if (p_which == this) {
-		current = true;
-	} else {
-		current = false;
+		new_current = true;
+	}
+
+	if (new_current != current) {
+		current = new_current;
+		_update_process_mode();
 	}
 }
 
@@ -413,6 +436,7 @@ void Camera2D::_set_current(bool p_current) {
 	}
 
 	current = p_current;
+	_update_process_mode();
 	update();
 }
 
@@ -427,13 +451,15 @@ void Camera2D::make_current() {
 		get_tree()->call_group_flags(SceneTree::GROUP_CALL_REALTIME, group_name, "_make_current", this);
 	}
 	_update_scroll();
+	_update_process_mode();
 }
 
 void Camera2D::clear_current() {
 	current = false;
 	if (is_inside_tree()) {
 		get_tree()->call_group_flags(SceneTree::GROUP_CALL_REALTIME, group_name, "_make_current", (Object *)nullptr);
 	}
+	_update_process_mode();
 }
 
 void Camera2D::set_limit(Margin p_margin, int p_limit) {

scene/2d/camera_2d.h

@@ -94,6 +94,11 @@ class Camera2D : public Node2D {
 
 	Camera2DProcessMode process_mode;
 
+	struct InterpolationData {
+		Transform2D xform_curr;
+		Transform2D xform_prev;
+	} _interpolation_data;
+
 protected:
 	virtual Transform2D get_camera_transform();
 	void _notification(int p_what);

scene/2d/canvas_item.cpp

@@ -562,6 +562,10 @@ void CanvasItem::_exit_canvas() {
 	}
 }
 
+void CanvasItem::_physics_interpolated_changed() {
+	VisualServer::get_singleton()->canvas_item_set_interpolated(canvas_item, is_physics_interpolated());
+}
+
 void CanvasItem::_notification(int p_what) {
 	switch (p_what) {
 		case NOTIFICATION_ENTER_TREE: {
@@ -605,6 +609,12 @@ void CanvasItem::_notification(int p_what) {
 			}
 			global_invalid = true;
 		} break;
+		case NOTIFICATION_RESET_PHYSICS_INTERPOLATION: {
+			if (is_visible_in_tree() && is_physics_interpolated()) {
+				VisualServer::get_singleton()->canvas_item_reset_physics_interpolation(canvas_item);
+			}
+		} break;
+
 		case NOTIFICATION_DRAW:
 		case NOTIFICATION_TRANSFORM_CHANGED: {
 		} break;

scene/2d/canvas_item.h

@@ -236,6 +236,7 @@ class CanvasItem : public Node {
 	}
 
 	void item_rect_changed(bool p_size_changed = true);
+	virtual void _physics_interpolated_changed();
 
 	void _notification(int p_what);
 	static void _bind_methods();

scene/3d/visual_instance.cpp

@@ -117,17 +117,6 @@ void VisualInstance::_notification(int p_what) {
 			if (_is_vi_visible() && is_physics_interpolated()) {
 				VisualServer::get_singleton()->instance_reset_physics_interpolation(instance);
 			}
-#if defined(DEBUG_ENABLED) && defined(TOOLS_ENABLED)
-			else if (GLOBAL_GET("debug/settings/physics_interpolation/enable_warnings")) {
-				String node_name = is_inside_tree() ? String(get_path()) : String(get_name());
-				if (!_is_vi_visible()) {
-					WARN_PRINT("[Physics interpolation] NOTIFICATION_RESET_PHYSICS_INTERPOLATION only works with unhidden nodes: \"" + node_name + "\".");
-				}
-				if (!is_physics_interpolated()) {
-					WARN_PRINT("[Physics interpolation] NOTIFICATION_RESET_PHYSICS_INTERPOLATION only works with interpolated nodes: \"" + node_name + "\".");
-				}
-			}
-#endif
 		} break;
 		case NOTIFICATION_EXIT_WORLD: {
 			VisualServer::get_singleton()->instance_set_scenario(instance, RID());

scene/gui/control.cpp

@@ -3003,6 +3003,8 @@ Control::Control() {
 	}
 	data.focus_mode = FOCUS_NONE;
 	data.modal_prev_focus_owner = 0;
+
+	set_physics_interpolation_mode(Node::PHYSICS_INTERPOLATION_MODE_OFF);
 }
 
 Control::~Control() {

scene/main/scene_tree.cpp

@@ -553,6 +553,12 @@ void SceneTree::client_physics_interpolation_remove_spatial(SelfList<Spatial> *p
 	_client_physics_interpolation._spatials_list.remove(p_elem);
 }
 
+void SceneTree::iteration_prepare() {
+	if (_physics_interpolation_enabled) {
+		VisualServer::get_singleton()->tick();
+	}
+}
+
 void SceneTree::iteration_end() {
 	// When physics interpolation is active, we want all pending transforms
 	// to be flushed to the VisualServer before finishing a physics tick.
@@ -566,10 +572,6 @@ bool SceneTree::iteration(float p_time) {
 
 	current_frame++;
 
-	if (_physics_interpolation_enabled) {
-		VisualServer::get_singleton()->tick();
-	}
-
 	// Any objects performing client physics interpolation
 	// should be given an opportunity to keep their previous transforms
 	// up to take before each new physics tick.

scene/main/scene_tree.h

@@ -313,6 +313,7 @@ class SceneTree : public MainLoop {
 	virtual void input_event(const Ref<InputEvent> &p_event);
 	virtual void init();
 
+	virtual void iteration_prepare();
 	virtual bool iteration(float p_time);
 	virtual void iteration_end();
 	virtual bool idle(float p_time);