From a9ba15f93b5fc4cef2c1880caf885371f7a1d84b Mon Sep 17 00:00:00 2001
From: Sara <sara@saragerretsen.nl>
Date: Sat, 24 Jun 2023 22:42:38 +0200
Subject: [PATCH] improved handling of interpolate_move calls with a distance
 shorter than minimum delta

---
 src/corelib/physics.c | 94 ++++++++++++++++++-------------------------
 1 file changed, 40 insertions(+), 54 deletions(-)

diff --git a/src/corelib/physics.c b/src/corelib/physics.c
index 2f6ad1c..64df3ef 100644
--- a/src/corelib/physics.c
+++ b/src/corelib/physics.c
@@ -179,91 +179,77 @@ float get_solve_force(const object_t* a, const object_t* b, float* out_px, float
 }
 
 static inline
-void _solve_collision_slide(object_t* this, object_t* other, float old_x, float old_y, float new_x, float new_y) {
+void _solve_collision_slide(object_t* this, object_t* other) {
 	float dx, dy;
 	const float d = get_solve_force(this, other, &dx, &dy);
 	this->sprite.x += dx;
 	this->sprite.y += dy;
-	
-	return;
-	this->sprite.x = old_x;
-	this->sprite.y = new_y;
-	if(!_collision_check(other, this)) {
-		return;
-	}
+}
 
-	this->sprite.x = new_x;
-	this->sprite.y = old_y;
-	if(!_collision_check(other, this)) {
-		return;
-	}
-
-	this->sprite.x = old_x;
-	this->sprite.y = old_y;
-	if(!_collision_check(other, this)) {
-		return;
+static inline
+void _solve_move(object_t* this) {
+	// loop over all objects and check collision if applicable
+	for(int i = 0; i < WORLD_NUM_OBJECTS; ++i) {
+		// get pointer to other object
+		object_t* other = g_objects + i;
+		// check collision, return if found
+		if(can_collide(other) && this != other && _collision_check(other, this)) {
+			object_broadcast_collision(other, this);
+			object_broadcast_collision(this, other);
+			_solve_collision_slide(this, other);
+		}
 	}
 }
 
-void interpolate_move(object_t* object, const float target_x, const float target_y, const float max_step_size, const int slide) {
+void interpolate_move(object_t* this, const float target_x, const float target_y, const float max_step_size, const int slide) {
 	// calculate step delta
-	float dx = target_x - object->sprite.x, dy = target_y - object->sprite.y;
+	float dx = target_x - this->sprite.x, dy = target_y - this->sprite.y;
 	if(dx == 0 && dy == 0)
 		return;
 	// calculate direction x,y
 	float m = sqrtf(dx*dx + dy*dy);
-	if(dx != 0)
-		dx /= m;
-	if(dy != 0)
-		dy /= m;
+	dx /= m;
+	dy /= m;
 	dx *= max_step_size; dy *= max_step_size;
 	int step_count = max_step_size / m;
 
 	// ensure this object would ever collide
 	// if it wouldn't collide anyway, just set position
-	if(!can_collide(object)) {
-		object->sprite.x = target_x;
-		object->sprite.y = target_y;
+	if(!can_collide(this)) {
+		this->sprite.x = target_x;
+		this->sprite.y = target_y;
 		return;
 	}
 
+	if(step_count == 0) {
+		this->sprite.x = target_x;
+		this->sprite.y = target_y;
+		_solve_move(this);
+	}
+
 	/*
 	 * 1. move towards target
 	 * 2. check collision with every other object
 	 */
-	for(int steps = 0; steps < step_count && (object->sprite.x != target_x || object->sprite.y != target_y); ++steps) {
+	for(int steps = 0; steps <= step_count && (this->sprite.x != target_x || this->sprite.y != target_y); ++steps) {
 		// move towards target, snap to target if distance is too low
-		const float old_x = object->sprite.x, old_y = object->sprite.y;
+		const float old_x = this->sprite.x, old_y = this->sprite.y;
 		float new_x, new_y;
 
-		const float distx = fabsf(object->sprite.x - target_x), disty = fabsf(object->sprite.y - target_y);
+		const float distx = fabsf(this->sprite.x - target_x), disty = fabsf(this->sprite.y - target_y);
 		const float sqdist = distx*distx + disty*disty;
-		if(sqdist > max_step_size) {
-			object->sprite.x += dx;
-			object->sprite.y += dy;
-			new_x = object->sprite.x;
-			new_y = object->sprite.y;
+		if(sqdist > max_step_size*max_step_size) {
+			this->sprite.x += dx;
+			this->sprite.y += dy;
+			new_x = this->sprite.x;
+			new_y = this->sprite.y;
 		} else {
-			new_x = object->sprite.x = target_x;
-			new_y = object->sprite.y = target_y;
+			this->sprite.x = target_x;
+			this->sprite.y = target_y;
+			new_x = target_x;
+			new_y = target_y;
 		}
 
-		// loop over all objects and check collision if applicable
-		for(int i = 0; i < WORLD_NUM_OBJECTS; ++i) {
-			// get pointer to other object
-			object_t* other = g_objects + i;
-			// check collision, return if found
-			if(can_collide(other) && object != other && _collision_check(other, object)) {
-				object_broadcast_collision(other, object);
-				object_broadcast_collision(object, other);
-				if(slide) {
-					_solve_collision_slide(object, other, old_x, old_y, new_x, new_y);
-				} else {
-					object->sprite.x = old_x;
-					object->sprite.y = old_y;
-					return;
-				}
-			}
-		}
+		_solve_move(this);
 	}
 }
-- 
2.34.1