/*********************************
*  Balls can be thrown about and 
*  softly bounce off one another 
**********************************/

// Physical variables to play with
var acceleration = 0.05;    // Force of throw
var drag = 0.975;           // Air resistance
var friction = 0.85;        // Wall bounciness
var gravity = 0.5;          // Force due to gravity

var numBalls = 5;           // Number of balls

var ballX = 0;             // where balls will come from
var ballY = 0;             

// Ball object with a position, speed and colour
var Ball = function(x, y, r, c){
    this.x = x;
    this.y = y;
    this.r = r;
    this.c = c;
    
    this.dx = (mouseX - ballX)/30*1.5;
    this.dy = (mouseY - ballY)/33*1.5;
    
    // Move ball based on its velocity
    this.move = function(){
        this.dx *= drag;
        this.dy *= drag;
        this.x += this.dx;
        this.y += this.dy;
    };
    
    // Bounce off walls
    this.bounce = function(){
        if (this.x < this.r) {
            this.x = this.r;
            this.dx *= -friction;
        }
        if (this.x > 400 - this.r){
            this.x = 400 - this.r;
            this.dx *= -friction;
        }
        if (this.y < this.r) {
            this.y = this.r;
            this.dy *= -friction;
        }
        if (this.y > 400 - this.r){
            this.y = 400 - this.r;
            this.dy *= -friction;
        }
    };
    
    // Test whether mouse is over ball
    this.selected = function() {
        if (abs(mouseX - this.x) < this.r && 
            abs(mouseY - this.y) < this.r) {
                return true;
        }
    };
    
    this.collide = function(that) {
        var dx = this.x - that.x;
        var dy = this.y - that.y;
        var dr = this.r + that.r;
        
        if (dx * dx + dy * dy < dr * dr){
            var theta = atan2(dy, dx);
            var force = (dr - sqrt(dx*dx + dy*dy));
            this.dx += force * cos(theta);
            that.dx -= force * cos(theta);
            this.dy += force * sin(theta);
            that.dy -= force * sin(theta);
        }
    };
    
};

var drawCannon = function() {
    
    var rotateValue = atan(mouseY/mouseX);
    rotate(rotateValue);
    
    fill(255, 0, 0, 50);
    ellipse(0, 0, 114, 27);
    
    rotate(-rotateValue);
};

var balls = [];
for (var b=0; b<numBalls; b++) {
    var r = 5 + round(random() * 35);
    var x = r + round(random() * (400 - 2 * r));
    var y = r + round(random() * (400 - 2 * r));
    var c = color(40, 60, 160, 200);
    balls.push(new Ball(x, y, r, c));
}

noStroke();
var selectedBall = false;

var i, j, ball;
var draw = function() {
    // Clear everything
    background(250, 247, 240);
    
    // Draw balls
    for (i=0; i<numBalls; i++) {
        ball = balls[i];
        fill(ball.c);
        ellipse(ball.x, ball.y, ball.r*2, ball.r*2);
    }
    
    // draw cannon
    drawCannon();

    // Calculate acceleration
    for (i=0; i<numBalls; i++) {
        if (balls[i] !== selectedBall) {
            balls[i].dy += gravity;
        }
        for (j=i; j<numBalls; j++){
            balls[i].collide(balls[j]);
        }
    }
    
    var mouseAngle = atan(mouseY/mouseX);
    ballX = cos(mouseAngle) * 58;
    ballY = sin(mouseAngle) * 58;
    
    // shoot a ball
    if (mouseIsPressed && millis()%4 === 3) {
        balls.push(new Ball(ballX, ballY, 10, 
                    color(40, 60, 160, 200)));
        numBalls++;
    }
    
    // Move balls
    for (i=0; i<numBalls; i++) {
        ball = balls[i];
        ball.move();
        ball.bounce();
    }
};

// Let go when mouse leaves canvas
var mouseOut = function(){
    mouseIsPressed = false;
};