Merge pull request #50063 from nekomatata/more-accurate-move-and-slide

Make move_and_slide collision detection more accurate

4 files changed, 154 insertions, 69 deletions

diff --git a/scene/2d/physics_body_2d.cpp b/scene/2d/physics_body_2d.cpp
index be619ed60d..80aa99bf5e 100644
--- a/scene/2d/physics_body_2d.cpp
+++ b/scene/2d/physics_body_2d.cpp
@@ -86,11 +86,11 @@ bool PhysicsBody2D::move_and_collide(const Vector2 &p_motion, bool p_infinite_in
 	// Restore direction of motion to be along original motion,
 	// in order to avoid sliding due to recovery,
 	// but only if collision depth is low enough to avoid tunneling.
-	real_t motion_length = p_motion.length();
-	if (motion_length > CMP_EPSILON) {
+	if (p_cancel_sliding) {
+		real_t motion_length = p_motion.length();
 		real_t precision = 0.001;
 
-		if (colliding && p_cancel_sliding) {
+		if (colliding) {
 			// Can't just use margin as a threshold because collision depth is calculated on unsafe motion,
 			// so even in normal resting cases the depth can be a bit more than the margin.
 			precision += motion_length * (r_result.collision_unsafe_fraction - r_result.collision_safe_fraction);
@@ -101,16 +101,21 @@ bool PhysicsBody2D::move_and_collide(const Vector2 &p_motion, bool p_infinite_in
 		}
 
 		if (p_cancel_sliding) {
+			// When motion is null, recovery is the resulting motion.
+			Vector2 motion_normal;
+			if (motion_length > CMP_EPSILON) {
+				motion_normal = p_motion / motion_length;
+			}
+
 			// Check depth of recovery.
-			Vector2 motion_normal = p_motion / motion_length;
-			real_t dot = r_result.motion.dot(motion_normal);
-			Vector2 recovery = r_result.motion - motion_normal * dot;
+			real_t projected_length = r_result.motion.dot(motion_normal);
+			Vector2 recovery = r_result.motion - motion_normal * projected_length;
 			real_t recovery_length = recovery.length();
 			// Fixes cases where canceling slide causes the motion to go too deep into the ground,
-			// Becauses we're only taking rest information into account and not general recovery.
+			// because we're only taking rest information into account and not general recovery.
 			if (recovery_length < (real_t)p_margin + precision) {
 				// Apply adjustment to motion.
-				r_result.motion = motion_normal * dot;
+				r_result.motion = motion_normal * projected_length;
 				r_result.remainder = p_motion - r_result.motion;
 			}
 		}
@@ -978,8 +983,9 @@ void CharacterBody2D::move_and_slide() {
 	floor_normal = Vector2();
 	floor_velocity = Vector2();
 
-	// No sliding on first attempt to keep floor motion stable when possible.
-	bool sliding_enabled = false;
+	// No sliding on first attempt to keep floor motion stable when possible,
+	// when stop on slope is enabled.
+	bool sliding_enabled = !stop_on_slope;
 	for (int iteration = 0; iteration < max_slides; ++iteration) {
 		PhysicsServer2D::MotionResult result;
 		bool found_collision = false;
@@ -1018,7 +1024,11 @@ void CharacterBody2D::move_and_slide() {
 						if (stop_on_slope) {
 							if ((body_velocity_normal + up_direction).length() < 0.01) {
 								Transform2D gt = get_global_transform();
-								gt.elements[2] -= result.motion.slide(up_direction);
+								if (result.motion.length() > margin) {
+									gt.elements[2] -= result.motion.slide(up_direction);
+								} else {
+									gt.elements[2] -= result.motion;
+								}
 								set_global_transform(gt);
 								linear_velocity = Vector2();
 								return;
@@ -1054,7 +1064,7 @@ void CharacterBody2D::move_and_slide() {
 	// Apply snap.
 	Transform2D gt = get_global_transform();
 	PhysicsServer2D::MotionResult result;
-	if (move_and_collide(snap, infinite_inertia, result, margin, false, true)) {
+	if (move_and_collide(snap, infinite_inertia, result, margin, false, true, false)) {
 		bool apply = true;
 		if (up_direction != Vector2()) {
 			if (Math::acos(result.collision_normal.dot(up_direction)) <= floor_max_angle + FLOOR_ANGLE_THRESHOLD) {
@@ -1065,9 +1075,12 @@ void CharacterBody2D::move_and_slide() {
 				if (stop_on_slope) {
 					// move and collide may stray the object a bit because of pre un-stucking,
 					// so only ensure that motion happens on floor direction in this case.
-					result.motion = up_direction * up_direction.dot(result.motion);
+					if (result.motion.length() > margin) {
+						result.motion = up_direction * up_direction.dot(result.motion);
+					} else {
+						result.motion = Vector2();
+					}
 				}
-
 			} else {
 				apply = false;
 			}
diff --git a/scene/3d/physics_body_3d.cpp b/scene/3d/physics_body_3d.cpp
index e7482d35e7..4568145458 100644
--- a/scene/3d/physics_body_3d.cpp
+++ b/scene/3d/physics_body_3d.cpp
@@ -125,11 +125,11 @@ bool PhysicsBody3D::move_and_collide(const Vector3 &p_motion, bool p_infinite_in
 	// Restore direction of motion to be along original motion,
 	// in order to avoid sliding due to recovery,
 	// but only if collision depth is low enough to avoid tunneling.
-	real_t motion_length = p_motion.length();
-	if (motion_length > CMP_EPSILON) {
-		real_t precision = CMP_EPSILON;
+	if (p_cancel_sliding) {
+		real_t motion_length = p_motion.length();
+		real_t precision = 0.001;
 
-		if (colliding && p_cancel_sliding) {
+		if (colliding) {
 			// Can't just use margin as a threshold because collision depth is calculated on unsafe motion,
 			// so even in normal resting cases the depth can be a bit more than the margin.
 			precision += motion_length * (r_result.collision_unsafe_fraction - r_result.collision_safe_fraction);
@@ -140,16 +140,21 @@ bool PhysicsBody3D::move_and_collide(const Vector3 &p_motion, bool p_infinite_in
 		}
 
 		if (p_cancel_sliding) {
+			// When motion is null, recovery is the resulting motion.
+			Vector3 motion_normal;
+			if (motion_length > CMP_EPSILON) {
+				motion_normal = p_motion / motion_length;
+			}
+
 			// Check depth of recovery.
-			Vector3 motion_normal = p_motion / motion_length;
-			real_t dot = r_result.motion.dot(motion_normal);
-			Vector3 recovery = r_result.motion - motion_normal * dot;
+			real_t projected_length = r_result.motion.dot(motion_normal);
+			Vector3 recovery = r_result.motion - motion_normal * projected_length;
 			real_t recovery_length = recovery.length();
 			// Fixes cases where canceling slide causes the motion to go too deep into the ground,
-			// Becauses we're only taking rest information into account and not general recovery.
+			// because we're only taking rest information into account and not general recovery.
 			if (recovery_length < (real_t)p_margin + precision) {
 				// Apply adjustment to motion.
-				r_result.motion = motion_normal * dot;
+				r_result.motion = motion_normal * projected_length;
 				r_result.remainder = p_motion - r_result.motion;
 			}
 		}
@@ -1012,8 +1017,9 @@ void CharacterBody3D::move_and_slide() {
 	floor_normal = Vector3();
 	floor_velocity = Vector3();
 
-	// No sliding on first attempt to keep motion stable when possible.
-	bool sliding_enabled = false;
+	// No sliding on first attempt to keep floor motion stable when possible,
+	// when stop on slope is enabled.
+	bool sliding_enabled = !stop_on_slope;
 	for (int iteration = 0; iteration < max_slides; ++iteration) {
 		PhysicsServer3D::MotionResult result;
 		bool found_collision = false;
@@ -1052,7 +1058,11 @@ void CharacterBody3D::move_and_slide() {
 						if (stop_on_slope) {
 							if ((body_velocity_normal + up_direction).length() < 0.01) {
 								Transform3D gt = get_global_transform();
-								gt.origin -= result.motion.slide(up_direction);
+								if (result.motion.length() > margin) {
+									gt.origin -= result.motion.slide(up_direction);
+								} else {
+									gt.origin -= result.motion;
+								}
 								set_global_transform(gt);
 								linear_velocity = Vector3();
 								return;
@@ -1094,7 +1104,7 @@ void CharacterBody3D::move_and_slide() {
 	// Apply snap.
 	Transform3D gt = get_global_transform();
 	PhysicsServer3D::MotionResult result;
-	if (move_and_collide(snap, infinite_inertia, result, margin, false, true)) {
+	if (move_and_collide(snap, infinite_inertia, result, margin, false, true, false)) {
 		bool apply = true;
 		if (up_direction != Vector3()) {
 			if (Math::acos(result.collision_normal.dot(up_direction)) <= floor_max_angle + FLOOR_ANGLE_THRESHOLD) {
@@ -1105,7 +1115,11 @@ void CharacterBody3D::move_and_slide() {
 				if (stop_on_slope) {
 					// move and collide may stray the object a bit because of pre un-stucking,
 					// so only ensure that motion happens on floor direction in this case.
-					result.motion = result.motion.project(up_direction);
+					if (result.motion.length() > margin) {
+						result.motion = result.motion.project(up_direction);
+					} else {
+						result.motion = Vector3();
+					}
 				}
 			} else {
 				apply = false; //snapped with floor direction, but did not snap to a floor, do not snap.
diff --git a/servers/physics_2d/space_2d_sw.cpp b/servers/physics_2d/space_2d_sw.cpp
index 4b123b2d46..cbde7144b7 100644
--- a/servers/physics_2d/space_2d_sw.cpp
+++ b/servers/physics_2d/space_2d_sw.cpp
@@ -283,22 +283,38 @@ bool PhysicsDirectSpaceState2DSW::cast_motion(const RID &p_shape, const Transfor
 			continue;
 		}
 
-		//just do kinematic solving
-		real_t low = 0;
-		real_t hi = 1;
 		Vector2 mnormal = p_motion.normalized();
 
+		//just do kinematic solving
+		real_t low = 0.0;
+		real_t hi = 1.0;
+		real_t fraction_coeff = 0.5;
 		for (int j = 0; j < 8; j++) { //steps should be customizable..
-
-			real_t ofs = (low + hi) * 0.5;
+			real_t fraction = low + (hi - low) * fraction_coeff;
 
 			Vector2 sep = mnormal; //important optimization for this to work fast enough
-			bool collided = CollisionSolver2DSW::solve(shape, p_xform, p_motion * ofs, col_obj->get_shape(shape_idx), col_obj_xform, Vector2(), nullptr, nullptr, &sep, p_margin);
+			bool collided = CollisionSolver2DSW::solve(shape, p_xform, p_motion * fraction, col_obj->get_shape(shape_idx), col_obj_xform, Vector2(), nullptr, nullptr, &sep, p_margin);
 
 			if (collided) {
-				hi = ofs;
+				hi = fraction;
+				if ((j == 0) || (low > 0.0)) { // Did it not collide before?
+					// When alternating or first iteration, use dichotomy.
+					fraction_coeff = 0.5;
+				} else {
+					// When colliding again, converge faster towards low fraction
+					// for more accurate results with long motions that collide near the start.
+					fraction_coeff = 0.25;
+				}
 			} else {
-				low = ofs;
+				low = fraction;
+				if ((j == 0) || (hi < 1.0)) { // Did it collide before?
+					// When alternating or first iteration, use dichotomy.
+					fraction_coeff = 0.5;
+				} else {
+					// When not colliding again, converge faster towards high fraction
+					// for more accurate results with long motions that collide near the end.
+					fraction_coeff = 0.75;
+				}
 			}
 		}
 
@@ -957,20 +973,35 @@ bool Space2DSW::test_body_motion(Body2DSW *p_body, const Transform2D &p_from, co
 				}
 
 				//just do kinematic solving
-				real_t low = 0;
-				real_t hi = 1;
-
+				real_t low = 0.0;
+				real_t hi = 1.0;
+				real_t fraction_coeff = 0.5;
 				for (int k = 0; k < 8; k++) { //steps should be customizable..
-
-					real_t ofs = (low + hi) * 0.5;
+					real_t fraction = low + (hi - low) * fraction_coeff;
 
 					Vector2 sep = motion_normal; //important optimization for this to work fast enough
-					bool collided = CollisionSolver2DSW::solve(body_shape, body_shape_xform, p_motion * ofs, against_shape, col_obj_shape_xform, Vector2(), nullptr, nullptr, &sep, 0);
+					bool collided = CollisionSolver2DSW::solve(body_shape, body_shape_xform, p_motion * fraction, against_shape, col_obj_shape_xform, Vector2(), nullptr, nullptr, &sep, 0);
 
 					if (collided) {
-						hi = ofs;
+						hi = fraction;
+						if ((k == 0) || (low > 0.0)) { // Did it not collide before?
+							// When alternating or first iteration, use dichotomy.
+							fraction_coeff = 0.5;
+						} else {
+							// When colliding again, converge faster towards low fraction
+							// for more accurate results with long motions that collide near the start.
+							fraction_coeff = 0.25;
+						}
 					} else {
-						low = ofs;
+						low = fraction;
+						if ((k == 0) || (hi < 1.0)) { // Did it collide before?
+							// When alternating or first iteration, use dichotomy.
+							fraction_coeff = 0.5;
+						} else {
+							// When not colliding again, converge faster towards high fraction
+							// for more accurate results with long motions that collide near the end.
+							fraction_coeff = 0.75;
+						}
 					}
 				}
 
diff --git a/servers/physics_3d/space_3d_sw.cpp b/servers/physics_3d/space_3d_sw.cpp
index eff480396d..cdae744ead 100644
--- a/servers/physics_3d/space_3d_sw.cpp
+++ b/servers/physics_3d/space_3d_sw.cpp
@@ -255,6 +255,8 @@ bool PhysicsDirectSpaceState3DSW::cast_motion(const RID &p_shape, const Transfor
 
 	bool best_first = true;
 
+	Vector3 motion_normal = p_motion.normalized();
+
 	Vector3 closest_A, closest_B;
 
 	for (int i = 0; i < amount; i++) {
@@ -270,7 +272,7 @@ bool PhysicsDirectSpaceState3DSW::cast_motion(const RID &p_shape, const Transfor
 		int shape_idx = space->intersection_query_subindex_results[i];
 
 		Vector3 point_A, point_B;
-		Vector3 sep_axis = p_motion.normalized();
+		Vector3 sep_axis = motion_normal;
 
 		Transform3D col_obj_xform = col_obj->get_transform() * col_obj->get_shape_transform(shape_idx);
 		//test initial overlap, does it collide if going all the way?
@@ -279,35 +281,47 @@ bool PhysicsDirectSpaceState3DSW::cast_motion(const RID &p_shape, const Transfor
 		}
 
 		//test initial overlap, ignore objects it's inside of.
-		sep_axis = p_motion.normalized();
+		sep_axis = motion_normal;
 
 		if (!CollisionSolver3DSW::solve_distance(shape, p_xform, col_obj->get_shape(shape_idx), col_obj_xform, point_A, point_B, aabb, &sep_axis)) {
 			continue;
 		}
 
 		//just do kinematic solving
-		real_t low = 0;
-		real_t hi = 1;
-		Vector3 mnormal = p_motion.normalized();
-
+		real_t low = 0.0;
+		real_t hi = 1.0;
+		real_t fraction_coeff = 0.5;
 		for (int j = 0; j < 8; j++) { //steps should be customizable..
+			real_t fraction = low + (hi - low) * fraction_coeff;
 
-			real_t ofs = (low + hi) * 0.5;
-
-			Vector3 sep = mnormal; //important optimization for this to work fast enough
-
-			mshape.motion = xform_inv.basis.xform(p_motion * ofs);
+			mshape.motion = xform_inv.basis.xform(p_motion * fraction);
 
 			Vector3 lA, lB;
-
+			Vector3 sep = motion_normal; //important optimization for this to work fast enough
 			bool collided = !CollisionSolver3DSW::solve_distance(&mshape, p_xform, col_obj->get_shape(shape_idx), col_obj_xform, lA, lB, aabb, &sep);
 
 			if (collided) {
-				hi = ofs;
+				hi = fraction;
+				if ((j == 0) || (low > 0.0)) { // Did it not collide before?
+					// When alternating or first iteration, use dichotomy.
+					fraction_coeff = 0.5;
+				} else {
+					// When colliding again, converge faster towards low fraction
+					// for more accurate results with long motions that collide near the start.
+					fraction_coeff = 0.25;
+				}
 			} else {
 				point_A = lA;
 				point_B = lB;
-				low = ofs;
+				low = fraction;
+				if ((j == 0) || (hi < 1.0)) { // Did it collide before?
+					// When alternating or first iteration, use dichotomy.
+					fraction_coeff = 0.5;
+				} else {
+					// When not colliding again, converge faster towards high fraction
+					// for more accurate results with long motions that collide near the end.
+					fraction_coeff = 0.75;
+				}
 			}
 		}
 
@@ -902,27 +916,40 @@ bool Space3DSW::test_body_motion(Body3DSW *p_body, const Transform3D &p_from, co
 				}
 
 				//just do kinematic solving
-				real_t low = 0;
-				real_t hi = 1;
-
+				real_t low = 0.0;
+				real_t hi = 1.0;
+				real_t fraction_coeff = 0.5;
 				for (int k = 0; k < 8; k++) { //steps should be customizable..
+					real_t fraction = low + (hi - low) * fraction_coeff;
 
-					real_t ofs = (low + hi) * 0.5;
-
-					Vector3 sep = motion_normal; //important optimization for this to work fast enough
-
-					mshape.motion = body_shape_xform_inv.basis.xform(p_motion * ofs);
+					mshape.motion = body_shape_xform_inv.basis.xform(p_motion * fraction);
 
 					Vector3 lA, lB;
-
+					Vector3 sep = motion_normal; //important optimization for this to work fast enough
 					bool collided = !CollisionSolver3DSW::solve_distance(&mshape, body_shape_xform, col_obj->get_shape(shape_idx), col_obj_xform, lA, lB, motion_aabb, &sep);
 
 					if (collided) {
-						hi = ofs;
+						hi = fraction;
+						if ((k == 0) || (low > 0.0)) { // Did it not collide before?
+							// When alternating or first iteration, use dichotomy.
+							fraction_coeff = 0.5;
+						} else {
+							// When colliding again, converge faster towards low fraction
+							// for more accurate results with long motions that collide near the start.
+							fraction_coeff = 0.25;
+						}
 					} else {
 						point_A = lA;
 						point_B = lB;
-						low = ofs;
+						low = fraction;
+						if ((k == 0) || (hi < 1.0)) { // Did it collide before?
+							// When alternating or first iteration, use dichotomy.
+							fraction_coeff = 0.5;
+						} else {
+							// When not colliding again, converge faster towards high fraction
+							// for more accurate results with long motions that collide near the end.
+							fraction_coeff = 0.75;
+						}
 					}
 				}