From 34d686e43ad4fc5ebe080df2019ad88bdaf750db Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Sat, 27 Mar 2021 17:00:25 -0400
Subject: ball: Bounce balls off each other

---
diff --git a/src/ball.c b/src/ball.c
index e37615b..a7ed27e 100644
--- a/src/ball.c
+++ b/src/ball.c
@@ -95,6 +95,15 @@ db_balls_move(struct db_ball *ball)
 	}
 }
 
+static void
+_db_ball_bounce(struct db_ball *ball, double col_x, double col_y)
+{
+	double col_a;
+
+	col_a = atan2(col_y - ball->y, col_x - ball->x) * 180 / M_PI;
+	ball->a = (2 * col_a - ball->a - 180) % 360;
+}
+
 void
 db_balls_collisions(struct db_ball *ball)
 {
@@ -109,7 +118,8 @@ db_balls_collisions(struct db_ball *ball)
 						 ball->x,  ball->y,  ball->r,
 						other->x, other->y, other->r,
 						&col_x, &col_y)) {
-				/* TODO: Reverse direction */
+				_db_ball_bounce(ball , col_x, col_y);
+				_db_ball_bounce(other, col_x, col_y);
 			}
 		}
 	}
--
cgit v0.9.1