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ball.velocityx = ball.velocityx*−1;

ball.nextx =ball.radius;

} else if (ball.nexty+ball.radius > theCanvas.height ) {

ball.velocityy = ball.velocityy*−1;

ball.nexty = theCanvas.height − ball.radius;

} else if(ball.nexty-ball.radius < 0) {

ball.velocityy = ball.velocityy*−1;

ball.nexty = ball.radius;

}

}

}

function render() {

var ball;

context.fillStyle = "#000000";

for (var i = 0; i ball = balls[i];

ball.x = ball.nextx;

ball.y = ball.nexty;

context.beginPath();

context.arc(ball.x,ball.y,ball.radius,0,Math.PI*2,true);

context.closePath();

context.fill();

}

}

function collide() {

var ball;

var testBall;

for (var i = 0; i ball = balls[i];

for (var j = i+1; j < balls.length; j++) {

testBall = balls[j];

if (hitTestCircle(ball,testBall)) {

collideBalls(ball,testBall);

}

}

}

}

function hitTestCircle(ball1,ball2) {

var retval = false;

var dx = ball1.nextx - ball2.nextx;

var dy = ball1.nexty - ball2.nexty;

var distance = (dx * dx + dy * dy);

if (distance <= (ball1.radius + ball2.radius) * (ball1.radius + ball2.radius) ) {

retval = true;

}

return retval;

}

function collideBalls(ball1,ball2) {

var dx = ball1.nextx - ball2.nextx;

var dy = ball1.nexty - ball2.nexty;

var collisionAngle = Math.atan2(dy, dx);

var speed1 = Math.sqrt(ball1.velocityx * ball1.velocityx +

ball1.velocityy * ball1.velocityy);

var speed2 = Math.sqrt(ball2.velocityx * ball2.velocityx +

ball2.velocityy * ball2.velocityy);

var direction1 = Math.atan2(ball1.velocityy, ball1.velocityx);

var direction2 = Math.atan2(ball2.velocityy, ball2.velocityx);

var velocityx_1 = speed1 * Math.cos(direction1 - collisionAngle);

var velocityy_1 = speed1 * Math.sin(direction1 - collisionAngle);

var velocityx_2 = speed2 * Math.cos(direction2 - collisionAngle);

var velocityy_2 = speed2 * Math.sin(direction2 - collisionAngle);

var final_velocityx_1 = ((ball1.mass - ball2.mass) * velocityx_1 +

(ball2.mass + ball2.mass) * velocityx_2)/(ball1.mass + ball2.mass);

var final_velocityx_2 = ((ball1.mass + ball1.mass) * velocityx_1 +

(ball2.mass - ball1.mass) * velocityx_2)/(ball1.mass + ball2.mass);

var final_velocityy_1 = velocityy_1;

var final_velocityy_2 = velocityy_2;

ball1.velocityx = Math.cos(collisionAngle) * final_velocityx_1 +

Math.cos(collisionAngle + Math.PI/2) * final_velocityy_1;

ball1.velocityy = Math.sin(collisionAngle) * final_velocityx_1 +

Math.sin(collisionAngle + Math.PI/2) * final_velocityy_1;

ball2.velocityx = Math.cos(collisionAngle) * final_velocityx_2 +

Math.cos(collisionAngle + Math.PI/2) * final_velocityy_2;

ball2.velocityy = Math.sin(collisionAngle) * final_velocityx_2 +

Math.sin(collisionAngle + Math.PI/2) * final_velocityy_2;

ball1.nextx = (ball1.nextx += ball1.velocityx);

ball1.nexty = (ball1.nexty += ball1.velocityy);

ball2.nextx = (ball2.nextx += ball2.velocityx);

ball2.nexty = (ball2.nexty += ball2.velocityy);

}

var numBalls = 200 ;

var maxSize = 15;

var minSize = 5;

var maxSpeed = maxSize+5;

var balls = new Array();

var tempBall;

var tempX;

var tempY;

var tempSpeed;

var tempAngle;

var tempRadius;

var tempRadians;

var tempvelocityx;

var tempvelocityy;

theCanvas = document.getElementById("canvasOne");

context = theCanvas.getContext("2d");

for (var i = 0; i < numBalls; i++) {

tempRadius = 5;

var placeOK = false;

while (!placeOK) {

tempX = tempRadius*3 + (Math.floor(Math.random()*theCanvas.width)-tempRadius*3);

tempY = tempRadius*3 + (Math.floor(Math.random()*theCanvas.height)-tempRadius*3);

tempSpeed = 4;

tempAngle = Math.floor(Math.random()*360);

tempRadians = tempAngle * Math.PI/ 180;

tempvelocityx = Math.cos(tempRadians) * tempSpeed;

tempvelocityy = Math.sin(tempRadians) * tempSpeed;

tempBall = {x:tempX,y:tempY, nextX: tempX, nextY: tempY, radius:tempRadius,

speed:tempSpeed, angle:tempAngle, velocityx:tempvelocityx,

velocityy:tempvelocityy, mass:tempRadius};

placeOK = canStartHere(tempBall);

}

balls.push(tempBall);

}