From a36d061c8e18122c44cf5ad6e8317f03bc3531eb Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Thu, 25 Mar 2021 18:28:11 -0400
Subject: ball: Convert loops to recursions

---
diff --git a/src/ball.c b/src/ball.c
index 7fd7660..826b210 100644
--- a/src/ball.c
+++ b/src/ball.c
@@ -60,43 +60,39 @@ db_ball_new(int x, int y, int r, int a, int d, int sr, double s,
 	return ball;
 }
 
-static void
-_db_ball_collisions(struct db_ball *this)
+void
+db_balls_collisions(struct db_ball *ball)
 {
-	struct db_ball *that;
+	struct db_ball *other;
 	int             col_x;
 	int             col_y;
 
-	for (that = this->next; that != NULL; that = that->next) {
-		if (db_col_pt_cir_cir(this->x, this->y, this->r,
-					that->x, that->y, that->r,
+	for (; other != NULL; other = other->next) {
+		if (db_col_pt_cir_cir(ball->x, ball->y, ball->r,
+					other->x, other->y, other->r,
 					&col_x, &col_y)) {
 			/* TODO: Reverse direction */
 		}
 	}
-}
 
-void
-db_balls_collisions(struct db_ball *ball_head)
-{
-	struct db_ball *ball;
-
-	for (ball = ball_head; ball != NULL; ball = ball->next) {
-		_db_ball_collisions(ball);
+	if (ball->next != NULL) {
+		db_balls_collisions(ball->next);
 	}
 }
 
 int
-db_balls_player_collisions(struct db_ball *ball_head,
+db_balls_player_collisions(struct db_ball *ball,
 		int player_x, int player_y, int player_r)
 {
-	struct db_ball *ball;
+	if (db_col_cir_cir(ball->x, ball->y, ball->r,
+				player_x, player_y, player_r)) {
+		return 1;
+	}
 
-	for (ball = ball_head; ball != NULL; ball = ball->next) {
-		if (db_col_cir_cir(ball->x, ball->y, ball->r,
-					player_x, player_y, player_r)) {
-			return 1;
-		}
+	if (ball->next != NULL) {
+		return db_balls_player_collisions(ball->next,
+				player_x, player_y, player_r);
+	} else {
+		return 0;
 	}
-	return 0;
 }
--
cgit v0.9.1