多物体碰撞

private function onEnterFrame(event:Event):void {
for (var i:uint = 0; i < numBalls - 1; i++) {
var ball0:Ball = balls[i];
for (var j:uint = i + 1; j < numBalls; j++) {
var ball1:Ball = balls[j];
var dx:Number = ball1.x - ball0.x;
var dy:Number = ball1.y - ball0.y;
var dist:Number = Math.sqrt(dx * dx + dy * dy);
var minDist:Number = ball0.radius + ball1.radius;
if (dist < minDist) {
var angle:Number = Math.atan2(dy, dx);
var tx:Number = ball0.x + Math.cos(angle) * minDist;
var ty:Number = ball0.y + Math.sin(angle) * minDist;
var ax:Number = (tx - ball1.x) * spring;
var ay:Number = (ty - ball1.y) * spring;
ball0.vx -= ax;
ball0.vy -= ay;
ball1.vx += ax;
ball1.vy += ay;
}
}
}
for (i = 0; i < numBalls; i++) {
var ball:Ball = balls[i];
move(ball);
}
}
private function move(ball:Ball):void {
ball.vy += gravity;
ball.x += ball.vx;
ball.y += ball.vy;
if (ball.x + ball.radius > stage.stageWidth) {
ball.x = stage.stageWidth - ball.radius;
ball.vx *= bounce;
} else if (ball.x - ball.radius < 0) {
ball.x = ball.radius;
ball.vx *= bounce;
}
if (ball.y + ball.radius > stage.stageHeight) {
ball.y = stage.stageHeight - ball.radius;
ball.vy *= bounce;
} else if (ball.y - ball.radius < 0) {
ball.y = ball.radius;
ball.vy *= bounce;
}
}
}
}

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var angle:Number = Math.atan2(dy, dx);
var tx:Number = ball0.x + Math.cos(angle) * minDist;
var ty:Number = ball0.y + Math.sin(angle) * minDist;

等同于：

var tx:Number = ball0.x + dx / dist * minDist;
var ty:Number = ball0.y + dy / dist * minDist;