(buggy) fix for is_on_floor flickering

servers/physics_2d/physics_2d_server_sw.cpp

@@ -167,12 +167,14 @@ void Physics2DServerSW::_shape_col_cbk(const Vector2 &p_point_A, const Vector2 &
 	if (cbk->max == 0)
 		return;
 
+	Vector2 rel_dir = (p_point_A - p_point_B).normalized();
+	cbk->best_normal = -rel_dir; // negate for consistency with _RestCallbackData2D.best_normal
+
 	if (cbk->valid_dir != Vector2()) {
 		if (p_point_A.distance_squared_to(p_point_B) > cbk->valid_depth * cbk->valid_depth) {
 			cbk->invalid_by_dir++;
 			return;
 		}
-		Vector2 rel_dir = (p_point_A - p_point_B).normalized();
 
 		if (cbk->valid_dir.dot(rel_dir) < Math_SQRT12) { //sqrt(2)/2.0 - 45 degrees
 			cbk->invalid_by_dir++;

servers/physics_2d/physics_2d_server_sw.h

@@ -85,6 +85,7 @@ class Physics2DServerSW : public Physics2DServer {
 		int amount;
 		int passed;
 		int invalid_by_dir;
+		Vector2 best_normal;
 		Vector2 *ptr;
 	};
 

servers/physics_2d/space_2d_sw.cpp

@@ -736,7 +736,8 @@ bool Space2DSW::test_body_motion(Body2DSW *p_body, const Transform2D &p_from, co
 	ExcludedShapeSW excluded_shape_pairs[max_excluded_shape_pairs];
 	int excluded_shape_pair_count = 0;
 
-	float separation_margin = MIN(p_margin, MAX(0.0, p_motion.length() - CMP_EPSILON)); //don't separate by more than the intended motion
+	float pmotion_len = p_motion.length(); // we'll use this more than once, so precompute it
+	float separation_margin = MIN(p_margin, MAX(0.0, pmotion_len - CMP_EPSILON)); //don't separate by more than the intended motion
 
 	Transform2D body_transform = p_from;
 
@@ -816,10 +817,19 @@ bool Space2DSW::test_body_motion(Body2DSW *p_body, const Transform2D &p_from, co
 
 					int current_passed = cbk.passed; //save how many points passed collision
 					bool did_collide = false;
+					bool motion_is_parallel = false;
 
 					Shape2DSW *against_shape = col_obj->get_shape(shape_idx);
 					if (CollisionSolver2DSW::solve(body_shape, body_shape_xform, Vector2(), against_shape, col_obj_shape_xform, Vector2(), cbkres, cbkptr, NULL, separation_margin)) {
-						did_collide = cbk.passed > current_passed; //more passed, so collision actually existed
+						motion_is_parallel = (p_motion != Vector2()) && (fabsf(cbk.best_normal.dot(p_motion)) < (CMP_EPSILON * pmotion_len)); // multiplying by pmotion_len on the right is faster than normalizing p_motion on the left
+						if (cbk.passed > current_passed) { // more passed, so collision actually existed
+							if (!motion_is_parallel) { // if a shape is moving horizontally across a floor or vertically against a wall, don't knock them out of the floor or wall
+								did_collide = true;
+							} else {
+								cbk.amount--; // if the collision was parallel to motion, don't consider it when applying recover_motion
+							}
+						}
+						//did_collide = (cbk.passed > current_passed) && !motion_is_perpendicular; //more passed, so collision actually existed, and motion isn't perpendicular to the other shape
 					}
 
 					if (!did_collide && cbk.invalid_by_dir > 0) {