better collisions

1 files changed, 81 insertions, 0 deletions

diff --git a/collision.c b/collision.c
new file mode 100644
index 0000000..d377d39
--- /dev/null
+++ b/collision.c
@@ -0,0 +1,81 @@
+#include "balls.h"
+
+int
+iscollision(Point p, Point q) {
+	int dx, dy;
+
+	dx = p.x - q.x;
+	dy = p.y-q.y;
+	return (dx*dx + dy*dy) < 4*RADIUS*RADIUS;
+}
+
+/* TODO: remove
+int
+collision(Ball b1, Ball b2, Point *p) {
+	Point l1, l2, d;
+	int dx, dy, closestdistsq, backdist, mvmtveclen;
+
+	l1 = b1.p;
+	l2 = Pt(b.p.x+b.v.x, b.p.y+b.v.y);
+	d = closestpointonline(L(l1, l2), b2.p));
+
+	dx = b2.p.x - d.x;
+	dy = b2.p.y - d.y;
+	closestdistsq = dx*dx + dy*dy;
+
+	if (closestdistsq > 4*RADIUS*RADIUS)
+		return 0;
+
+	backdist = sqrt(4*RADIUS*RADIUS - closestdistsq);
+	mvmtveclen = vlen(b1.v);
+	p->x = d.x - backdist * (b1.v.x / mvmtveclen);
+	p->y = d.y - backdist * (b1.v.y / mvmtveclen);
+	return 1;
+}
+
+Vec
+vpostcollision(Ball b1, Ball b2) {
+	Point c1, c2;
+	int dcx, dcy, d;
+	Vec n;
+
+	if (!collision(b1, b2, &c1)) {
+		printf("warning: vpostcollision called, but no collision\n");
+		return b1.v;
+	}
+	if (!collision(b2, b1, &c2)) {
+		printf("warning: vpostcollision called, but no collision\n");
+		return b1.v;
+	}
+
+	d = norm(vsub(c1, c2));
+	n = V(dcx/d, dcy/d);
+	p = 2 * (vdot(b1.v, n) - vdot(b2.v, n)) / (b1.m + b2.m);
+	
+	b1.v.x = b1.v.x - p * b1.m * n.x;
+	b1.v.y = b1.v.y - p * b1.m * n.y;
+	return b1.v;
+}
+
+Point
+closestpointonline(Line l, Point p) {
+	int a, b, c1, c2, d;
+	Point c;
+	
+	a = l.p2.y - l.p1.y;
+	b = l.p1.x - l.p2.x;
+
+	c1 = a*l.p1.x + b*l.p1.y;
+	c2 = -b*p.x + a*p.y;
+
+	d = a*a - -b*b;
+	if (d != 0) {
+		c.x = (a*c1 - b*c2) / d;
+		c.y = (a*c2 + b*c1) / d;
+	} else {
+		c = p;
+	}
+
+	return c;
+}
+*/