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#include "balls.h"
static double clamp(double v, double lo, double hi);
static double min(double a, double b);
static double max(double a, double b);
int
isCollision(Point p1, double r1, Point p2, double r2) {
double dx, dy;
dx = p1.x - p2.x;
dy = p1.y - p2.y;
return (dx*dx + dy*dy) <= (r1+r2)*(r1+r2);
}
void
collideWall(Ball *b, Rectangle wall) {
wall = insetRect(wall, b->r);
if (b->p.x < wall.min.x || b->p.x > wall.max.x) {
b->p.x = clamp(b->p.x, wall.min.x, wall.max.x);
b->v.x = -b->v.x;
}
if (b->p.y < wall.min.y || b->p.y > wall.max.y) {
b->p.y = clamp(b->p.y, wall.min.y, wall.max.y);
b->v.y = -b->v.y;
}
}
void
collideBall(Ball *b1, Ball *b2) {
Point midpt;
Vector n, distv;
double mrat, coef;
if (!isCollision(b1->p, b1->r, b2->p, b2->r))
return;
/* set position of collision */
midpt = ptDivS(addPt(b1->p, b2->p), 2);
n = unitNorm(VecPt(b1->p, b2->p));
b1->p = ptSubVec(midpt, vecMulS(n, b1->r));
b2->p = ptAddVec(midpt, vecMulS(n, b2->r));
/* reaction velocity */
mrat = 2.0 * b2->m / (b1->m + b2->m);
distv = VecPt(b2->p, b1->p);
coef = vecDot(subVec(b1->v, b2->v), distv) / (vecLen(distv)*vecLen(distv));
b1->v = subVec(b1->v, vecMulS(distv, mrat*coef));
mrat = 2.0 * b1->m / (b1->m + b2->m);
distv = VecPt(b1->p, b2->p);
coef = vecDot(subVec(b2->v, b1->v), distv) / (vecLen(distv)*vecLen(distv));
b2->v = subVec(b2->v, vecMulS(distv, mrat*coef));
}
static double
clamp(double v, double lo, double hi) {
return min(hi, max(v, lo));
}
static double
min(double a, double b) {
return (a < b) ? a : b;
}
static double
max(double a, double b) {
return (a > b) ? a : b;
}
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