From bac35a3baba00984b08fffe42bd514eda6fd2894 Mon Sep 17 00:00:00 2001
From: Steve <stephenjsweeney@battleforthesolarsystem.com>
Date: Fri, 2 Feb 2018 18:14:50 +0000
Subject: [PATCH] Line box intersection code.

---
 src/util/util.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/util/util.c b/src/util/util.c
index 6509d5f..61923fd 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -25,6 +25,40 @@ int collision(int x1, int y1, int w1, int h1, int x2, int y2, int w2, int h2)
 	return (MAX(x1, x2) < MIN(x1 + w1, x2 + w2)) && (MAX(y1, y2) < MIN(y1 + h1, y2 + h2));
 }
 
+int lineLineIntersection(int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4)
+{
+	int d, n1, n2, ua, ub;
+
+	d = ((y4 - y3) * (x2 - x1)) - ((x4 - x3) * (y2 - y1));
+	n1 = ((x4 - x3) * (y1 - y3)) - ((y4 - y3) * (x1 - x3));
+	n2 = ((x2 - x1) * (y1 - y3)) - ((y2 - y1) * (x1 - x3));
+
+	if (d == 0)
+	{
+		if ( n1 == 0 && n2 == 0)
+		{
+			return 0;
+		}
+
+		return 0;
+	}
+	
+	ua = n1 / d;
+	ub = n2 / d;
+
+	return (ua >= 0 && ua <= 1 && ub >= 0 && ub <= 1);
+}
+
+int lineRectIntersection(int x1, int y1, int x2, int y2, SDL_Rect *r)
+{
+	return (
+		lineLineIntersection(x1, y1, x2, y2, r->x, r->y, r->x + r->w, r->y) || /* top */
+		lineLineIntersection(x1, y1, x2, y2, r->x, r->y + r->h, r->x + r->w, r->y + r->h) || /* bottom */
+		lineLineIntersection(x1, y1, x2, y2, r->x, r->y, r->x, r->y + r->h) || /* left */
+		lineLineIntersection(x1, y1, x2, y2, r->x + r->w, r->y, r->x + r->w, r->y + r->h) /* right */
+	);
+}
+
 char *timeToString(long millis, int showHours)
 {
 	static char TIME[MAX_NAME_LENGTH];