ruffrey/.block

## .block
license: mit

## README.md

      
    Raw
  

              README.md
            
          
    HTML5 Canvas Game - Pong example, with AI

Include pong.js then create an instance of new Pong and pass in the element where you would like for it to be rendered.
License

MIT

  
## HTML5 Canvas Ping Pong.md

      
    Raw
  

              HTML5 Canvas Ping Pong.md
            
          
    http://bl.ocks.org/ruffrey/1e242222aebbcd102a53


## index.html
<!doctype html>
<html>
    <head>
        <title>Pong</title>
        <script src="pong.js"></script>
    </head>
    <body>
        <div id="pong-game"></div>
        <script>
            new Pong('pong-game', window, document);
        </script>
    </body>
</html>

## LICENSE
Copyright 2014-2019 Jeff H. Parrish

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

## pong.js
'use strict';

/**
 * Settings
 */
var DIFFICULTY = 0.1; // from 0 to 1, 1 being hardest

var WIDTH = 200;
var HEIGHT = 300;
var PADDLEWIDTH = 50;
var LEFTARROW = 37;
var RIGHTARROW = 39;
var OFFWHITE = "#f9fafc";
var BLUE = "#3b79b4";

/**
 * Draws a rounded rectangle using the current state of the canvas.
 * If you omit the last three params, it will draw a rectangle
 * outline with a 5 pixel border radius
 * @param {CanvasRenderingContext2D} ctx
 * @param {Number} x The top left x coordinate
 * @param {Number} y The top left y coordinate
 * @param {Number} width The width of the rectangle
 * @param {Number} height The height of the rectangle
 * @param {Number} radius The corner radius. Defaults to 5;
 * @param {Boolean} fill Whether to fill the rectangle. Defaults to false.
 * @param {Boolean} stroke Whether to stroke the rectangle. Defaults to true.
 */
function roundRect(ctx, x, y, width, height, radius, fill, stroke) {
    if (typeof stroke === "undefined") {
        stroke = true;
    }
    if (typeof radius === "undefined") {
        radius = 5;
    }
    ctx.beginPath();
    ctx.moveTo(x + radius, y);
    ctx.lineTo(x + width - radius, y);
    ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
    ctx.lineTo(x + width, y + height - radius);
    ctx.quadraticCurveTo(x + width, y + height, x + width - radius, y + height);
    ctx.lineTo(x + radius, y + height);
    ctx.quadraticCurveTo(x, y + height, x, y + height - radius);
    ctx.lineTo(x, y + radius);
    ctx.quadraticCurveTo(x, y, x + radius, y);
    ctx.closePath();
    if (stroke) {
        ctx.stroke();
    }
    if (fill) {
        ctx.fill();
    }
}

/**
 * Simple randomization between a min and max.
 * @param {number} min
 * @param {number} max
 * @returns {number} A random number between two points.
 */
function randomOffset(min, max) {
    return (Math.random() * (max - min)) + min;
}


/**
 * The paddle which is later attached to player and computer.
 * @param {number} x
 * @param {number} y
 * @param {number} width
 * @param {number} height
 */
function Paddle(x, y) {
    this.width = PADDLEWIDTH;
    this.height = 10;

    this.x = x;
    this.y = y;
    this.x_speed = 0;
    this.y_speed = 0;
}
/**
 * Render the paddle on the canvas.
 * @param {CanvasContext} ctx
 */
Paddle.prototype.render = function (ctx) {
    roundRect(ctx, this.x, this.y, this.width, this.height, 5, true, null);
};
/**
 * Move the paddle position on the canvas.
 * @param {number} x
 * @param {number} y
 */
Paddle.prototype.move = function (x, y) {
    this.x += x;
    this.y += y;
    this.x_speed = x;
    this.y_speed = y;
    if (this.x < 0) {
        this.x = 0;
        this.x_speed = 0;
    }
    else if (this.x + this.width > WIDTH) {
        this.x = WIDTH - this.width;
        this.x_speed = 0;
    }
};

/**
 * The AI user.
 */
function Computer() {
    this.score = 0;
    var paddleX = (WIDTH / 2) - (PADDLEWIDTH / 2);
    var paddleY = 10;
    this.paddle = new Paddle(paddleX, paddleY);
}
Computer.prototype.render = function (ctx) {
    this.paddle.render(ctx);
    ctx.fillText(this.score.toString(), 5, 30);
};
/**
 * Computer automatically adjusts position based on ball position, with a calculated margin of error.
 */
Computer.prototype.update = function (ball) {
    var ball_x_position = ball.x;
    // difference between ball x and the paddle x
    var diff = -((this.paddle.x + (this.paddle.width / 2)) - ball_x_position);
    if (diff < 0 && diff < -4) {
        diff = -5;
    }
    else if (diff > 0 && diff > 4) {
        diff = 5;
    }

    // sets the difficulty, an offset between these two numbers
    this.paddle.move(diff * randomOffset(DIFFICULTY, 1), 0);

    if (this.paddle.x < 0) {
        this.paddle.x = 0;
    }
    else if (this.paddle.x + this.paddle.width > WIDTH) {
        this.paddle.x = WIDTH - this.paddle.width;
    }
};

/**
 * The human user.
 */
function Player() {
    this.score = 0;
    var paddleX = (WIDTH / 2) - (PADDLEWIDTH / 2);
    var paddleY = HEIGHT - 20;
    this.paddle = new Paddle(paddleX, paddleY);
}

Player.prototype.render = function (ctx) {
    this.paddle.render(ctx);
    ctx.fillText(this.score.toString(), 5, HEIGHT - 30);
};

Player.prototype.update = function (keysDown) {
    var value;
    for (var key in keysDown) {
        value = Number(key);
        if (value === LEFTARROW) {
            this.paddle.move(-4, 0);
        }
        else if (value === RIGHTARROW) {
            this.paddle.move(4, 0);
        }
        else {
            this.paddle.move(0, 0);
        }
    }
};

/**
 * A ball, which handles it's own internal "physics"
 * @param {number} x optional default x position
 * @param {number} y optional default y position
 * @param {number} speedX optional default x speed
 * @param {number} speedY optional default y speed
 * @param {number} rad optional default radius
 */
function Ball(x, y, speedX, speedY, rad) {
    // console.debug('Creating Ball', x, y, speedX, speedY, rad);
    this.radius = rad || 5;

    this.default_x_position = function () { return typeof x === 'undefined' ? WIDTH / 2 : x; };
    this.default_y_position = function () { return typeof y === 'undefined' ? HEIGHT / 2 : y; };

    this.default_x_speed = function () { return typeof speedX === 'undefined' ? 0 : speedX; };
    this.default_y_speed = function () { return typeof speedY === 'undefined' ? 3 : speedY; };

    this.resetSpeed = function () {
        this.x_speed = this.default_x_speed();
        this.y_speed = this.default_y_speed();
        // console.debug('Resetting Ball speed', this.x_speed, this.y_speed);
    };
    this.resetPosition = function () {
        this.x = this.default_x_position();
        this.y = this.default_y_position();
        // console.debug('Resetting Ball position', this.x, this.y);
    };

    this.reset = function () {
        this.resetSpeed();
        this.resetPosition();
    };

    this.reset();
}

Ball.prototype.render = function (ctx) {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 2 * Math.PI, false);
    ctx.fill();
};
/**
 * Ball movement is coded here. Score is determined when the ball moves.
 * Speed and position of the ball are determined internal to the ball object.
 */
Ball.prototype.update = function (playerBottom, playerTop) {
    // The speed is applied to the x and y positions of the ball, which moves the ball.
    this.x += this.x_speed;
    this.y += this.y_speed;

    var top_x = this.x - this.radius;
    var top_y = this.y - this.radius;
    var bottom_x = this.x + this.radius;
    var bottom_y = this.y + this.radius;
    var paddleBottom = playerBottom.paddle;
    var paddleTop = playerTop.paddle;

    // Figures out if the ball direction should change.
    var ballHitLeftWall = this.x - this.radius < 0;
    var ballHitRightWall = this.x + this.radius > WIDTH;
    if (ballHitLeftWall) {
        this.x = this.radius;
        this.x_speed = -this.x_speed;
    }
    else if (ballHitRightWall) {
        this.x = WIDTH - this.radius;
        this.x_speed = -this.x_speed;
    }

    // When somebody scores, reset the ball to the center.
    var bottomScored = this.y < 0;
    var topScored = this.y > 300;
    if (bottomScored || topScored) {

        if (bottomScored) {
            playerBottom.score++;
        }
        if (topScored) {
            playerTop.score++;
        }

        this.reset();
    }

    // Determines how much to change the ball speed.
    // When the ball hits a paddle:
    // the ball vertical trajectory reverses and gets set to a randomly but loosely based on the paddle speed,
    // and the horizontal speed increases by half the speed of the paddle.

    var ballInBottomOfScreen = top_y > (HEIGHT * 0.75);
    if (ballInBottomOfScreen) {

        var bottomPaddleYArea = paddleBottom.y + paddleBottom.height;
        var ballTopIsUnderBottomPaddle = top_y < bottomPaddleYArea;
        var ballBottomIsAboveBottomPaddle = bottom_y > paddleBottom.y;
        var ballYOverlapsBottomPaddle = ballTopIsUnderBottomPaddle && ballBottomIsAboveBottomPaddle;

        var bottomPaddleXArea = paddleBottom.x + paddleBottom.width;
        var ballXOverlapsBottomPaddle = top_x < bottomPaddleXArea && bottom_x > paddleBottom.x;

        var ballHitBottomPaddle = ballYOverlapsBottomPaddle && ballXOverlapsBottomPaddle;

        if (ballHitBottomPaddle) {
            this.y_speed = randomOffset(-(Math.abs(paddleBottom.x_speed || 4)), -0.9 * Math.abs(paddleBottom.x_speed || 4));
            this.x_speed += (paddleBottom.x_speed / 2);
            this.y += this.y_speed;
        }
    }
    else {
        var topPaddleBottom = paddleTop.y + paddleTop.height;
        var ballTopIsOverTopPaddle = top_y < topPaddleBottom;
        var ballBottomIsUnderTopPaddle = bottom_y > paddleTop.y;

        var ballXOverlapsTopPaddle = top_x < (paddleTop.x + paddleTop.width) && bottom_x > paddleTop.x;

        var ballHitTopPaddle = ballTopIsOverTopPaddle && ballBottomIsUnderTopPaddle && ballXOverlapsTopPaddle;

        if (ballHitTopPaddle) {
            this.y_speed = randomOffset(0.9 * Math.abs(paddleTop.x_speed || 4), Math.abs(paddleTop.x_speed || 4));
            this.x_speed += (paddleTop.x_speed / 2);
            this.y += this.y_speed;
        }
    }

};


/**
 * Play some pong.
 * @param string appendToElementId The id of the element you want to put pong inside.
 * @param object window
 * @param object document
 * @returns HTML5CanvasElement The canvas inside the element for which you supplied the id.
 */
function Pong(appendToElementId, window, document) {

    var el = document.getElementById(appendToElementId);
    var animate = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) {
        window.setTimeout(callback, 1000 / 60);
    };

    var canvas = document.createElement("canvas");
    canvas.width = WIDTH;
    canvas.height = HEIGHT;
    canvas.style.borderRadius = '5px';
    canvas.style.border = '2px solid ' + OFFWHITE;

    var context = canvas.getContext('2d');
    context.fillStyle = BLUE;
    context.font = "12px sans-serif";

    var player = new Player();
    var computer = new Computer();

    var ball = new Ball();

    var keysDown = {};


    function render() {
        context.fillStyle = OFFWHITE;
        context.fillRect(0, 0, canvas.width, canvas.height);
        context.fillStyle = BLUE;

        player.render(context);
        computer.render(context);
        ball.render(context);
    }

    function update() {
        player.update(keysDown);
        computer.update(ball);
        ball.update(player, computer);
    }

    function step() {
        update();
        render(context);
        animate(step);
    }


    el.appendChild(canvas);
    animate(step);

    var keydownEvent = function (event) {
        keysDown[event.keyCode] = true;
    };
    var keyupEvent = function (event) {
        delete keysDown[event.keyCode];
    };
    var elementDestroyed = function (event) {
        window.removeEventListener('keydown', keydownEvent, false);
        window.removeEventListener('keyup', keyupEvent, false);
        window.removeEventListener('DOMNodeRemoved', elementDestroyed, false);
    };

    window.addEventListener("keydown", keydownEvent);
    window.addEventListener("keyup", keyupEvent);
    window.addEventListener("DOMNodeRemoved", elementDestroyed);

    return el;
};
	<!doctype html>
	<html>
	<head>
	<title>Pong</title>
	<script src="pong.js"></script>
	</head>
	<body>
	<div id="pong-game"></div>
	<script>
	new Pong('pong-game', window, document);
	</script>
	</body>
	</html>
	Copyright 2014-2019 Jeff H. Parrish

	Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

	The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
	'use strict';

	/**
	* Settings
	*/
	var DIFFICULTY = 0.1; // from 0 to 1, 1 being hardest

	var WIDTH = 200;
	var HEIGHT = 300;
	var PADDLEWIDTH = 50;
	var LEFTARROW = 37;
	var RIGHTARROW = 39;
	var OFFWHITE = "#f9fafc";
	var BLUE = "#3b79b4";

	/**
	* Draws a rounded rectangle using the current state of the canvas.
	* If you omit the last three params, it will draw a rectangle
	* outline with a 5 pixel border radius
	* @param {CanvasRenderingContext2D} ctx
	* @param {Number} x The top left x coordinate
	* @param {Number} y The top left y coordinate
	* @param {Number} width The width of the rectangle
	* @param {Number} height The height of the rectangle
	* @param {Number} radius The corner radius. Defaults to 5;
	* @param {Boolean} fill Whether to fill the rectangle. Defaults to false.
	* @param {Boolean} stroke Whether to stroke the rectangle. Defaults to true.
	*/
	function roundRect(ctx, x, y, width, height, radius, fill, stroke) {
	if (typeof stroke === "undefined") {
	stroke = true;
	}
	if (typeof radius === "undefined") {
	radius = 5;
	}
	ctx.beginPath();
	ctx.moveTo(x + radius, y);
	ctx.lineTo(x + width - radius, y);
	ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
	ctx.lineTo(x + width, y + height - radius);
	ctx.quadraticCurveTo(x + width, y + height, x + width - radius, y + height);
	ctx.lineTo(x + radius, y + height);
	ctx.quadraticCurveTo(x, y + height, x, y + height - radius);
	ctx.lineTo(x, y + radius);
	ctx.quadraticCurveTo(x, y, x + radius, y);
	ctx.closePath();
	if (stroke) {
	ctx.stroke();
	}
	if (fill) {
	ctx.fill();
	}
	}

	/**
	* Simple randomization between a min and max.
	* @param {number} min
	* @param {number} max
	* @returns {number} A random number between two points.
	*/
	function randomOffset(min, max) {
	return (Math.random() * (max - min)) + min;
	}



	/**
	* The paddle which is later attached to player and computer.
	* @param {number} x
	* @param {number} y
	* @param {number} width
	* @param {number} height
	*/
	function Paddle(x, y) {
	this.width = PADDLEWIDTH;
	this.height = 10;

	this.x = x;
	this.y = y;
	this.x_speed = 0;
	this.y_speed = 0;
	}
	/**
	* Render the paddle on the canvas.
	* @param {CanvasContext} ctx
	*/
	Paddle.prototype.render = function (ctx) {
	roundRect(ctx, this.x, this.y, this.width, this.height, 5, true, null);
	};
	/**
	* Move the paddle position on the canvas.
	* @param {number} x
	* @param {number} y
	*/
	Paddle.prototype.move = function (x, y) {
	this.x += x;
	this.y += y;
	this.x_speed = x;
	this.y_speed = y;
	if (this.x < 0) {
	this.x = 0;
	this.x_speed = 0;
	}
	else if (this.x + this.width > WIDTH) {
	this.x = WIDTH - this.width;
	this.x_speed = 0;
	}
	};

	/**
	* The AI user.
	*/
	function Computer() {
	this.score = 0;
	var paddleX = (WIDTH / 2) - (PADDLEWIDTH / 2);
	var paddleY = 10;
	this.paddle = new Paddle(paddleX, paddleY);
	}
	Computer.prototype.render = function (ctx) {
	this.paddle.render(ctx);
	ctx.fillText(this.score.toString(), 5, 30);
	};
	/**
	* Computer automatically adjusts position based on ball position, with a calculated margin of error.
	*/
	Computer.prototype.update = function (ball) {
	var ball_x_position = ball.x;
	// difference between ball x and the paddle x
	var diff = -((this.paddle.x + (this.paddle.width / 2)) - ball_x_position);
	if (diff < 0 && diff < -4) {
	diff = -5;
	}
	else if (diff > 0 && diff > 4) {
	diff = 5;
	}

	// sets the difficulty, an offset between these two numbers
	this.paddle.move(diff * randomOffset(DIFFICULTY, 1), 0);

	if (this.paddle.x < 0) {
	this.paddle.x = 0;
	}
	else if (this.paddle.x + this.paddle.width > WIDTH) {
	this.paddle.x = WIDTH - this.paddle.width;
	}
	};

	/**
	* The human user.
	*/
	function Player() {
	this.score = 0;
	var paddleX = (WIDTH / 2) - (PADDLEWIDTH / 2);
	var paddleY = HEIGHT - 20;
	this.paddle = new Paddle(paddleX, paddleY);
	}

	Player.prototype.render = function (ctx) {
	this.paddle.render(ctx);
	ctx.fillText(this.score.toString(), 5, HEIGHT - 30);
	};

	Player.prototype.update = function (keysDown) {
	var value;
	for (var key in keysDown) {
	value = Number(key);
	if (value === LEFTARROW) {
	this.paddle.move(-4, 0);
	}
	else if (value === RIGHTARROW) {
	this.paddle.move(4, 0);
	}
	else {
	this.paddle.move(0, 0);
	}
	}
	};

	/**
	* A ball, which handles it's own internal "physics"
	* @param {number} x optional default x position
	* @param {number} y optional default y position
	* @param {number} speedX optional default x speed
	* @param {number} speedY optional default y speed
	* @param {number} rad optional default radius
	*/
	function Ball(x, y, speedX, speedY, rad) {
	// console.debug('Creating Ball', x, y, speedX, speedY, rad);
	this.radius = rad \|\| 5;

	this.default_x_position = function () { return typeof x === 'undefined' ? WIDTH / 2 : x; };
	this.default_y_position = function () { return typeof y === 'undefined' ? HEIGHT / 2 : y; };

	this.default_x_speed = function () { return typeof speedX === 'undefined' ? 0 : speedX; };
	this.default_y_speed = function () { return typeof speedY === 'undefined' ? 3 : speedY; };

	this.resetSpeed = function () {
	this.x_speed = this.default_x_speed();
	this.y_speed = this.default_y_speed();
	// console.debug('Resetting Ball speed', this.x_speed, this.y_speed);
	};
	this.resetPosition = function () {
	this.x = this.default_x_position();
	this.y = this.default_y_position();
	// console.debug('Resetting Ball position', this.x, this.y);
	};

	this.reset = function () {
	this.resetSpeed();
	this.resetPosition();
	};

	this.reset();
	}

	Ball.prototype.render = function (ctx) {
	ctx.beginPath();
	ctx.arc(this.x, this.y, this.radius, 2 * Math.PI, false);
	ctx.fill();
	};
	/**
	* Ball movement is coded here. Score is determined when the ball moves.
	* Speed and position of the ball are determined internal to the ball object.
	*/
	Ball.prototype.update = function (playerBottom, playerTop) {
	// The speed is applied to the x and y positions of the ball, which moves the ball.
	this.x += this.x_speed;
	this.y += this.y_speed;

	var top_x = this.x - this.radius;
	var top_y = this.y - this.radius;
	var bottom_x = this.x + this.radius;
	var bottom_y = this.y + this.radius;
	var paddleBottom = playerBottom.paddle;
	var paddleTop = playerTop.paddle;

	// Figures out if the ball direction should change.
	var ballHitLeftWall = this.x - this.radius < 0;
	var ballHitRightWall = this.x + this.radius > WIDTH;
	if (ballHitLeftWall) {
	this.x = this.radius;
	this.x_speed = -this.x_speed;
	}
	else if (ballHitRightWall) {
	this.x = WIDTH - this.radius;
	this.x_speed = -this.x_speed;
	}

	// When somebody scores, reset the ball to the center.
	var bottomScored = this.y < 0;
	var topScored = this.y > 300;
	if (bottomScored \|\| topScored) {

	if (bottomScored) {
	playerBottom.score++;
	}
	if (topScored) {
	playerTop.score++;
	}

	this.reset();
	}

	// Determines how much to change the ball speed.
	// When the ball hits a paddle:
	// the ball vertical trajectory reverses and gets set to a randomly but loosely based on the paddle speed,
	// and the horizontal speed increases by half the speed of the paddle.

	var ballInBottomOfScreen = top_y > (HEIGHT * 0.75);
	if (ballInBottomOfScreen) {

	var bottomPaddleYArea = paddleBottom.y + paddleBottom.height;
	var ballTopIsUnderBottomPaddle = top_y < bottomPaddleYArea;
	var ballBottomIsAboveBottomPaddle = bottom_y > paddleBottom.y;
	var ballYOverlapsBottomPaddle = ballTopIsUnderBottomPaddle && ballBottomIsAboveBottomPaddle;

	var bottomPaddleXArea = paddleBottom.x + paddleBottom.width;
	var ballXOverlapsBottomPaddle = top_x < bottomPaddleXArea && bottom_x > paddleBottom.x;

	var ballHitBottomPaddle = ballYOverlapsBottomPaddle && ballXOverlapsBottomPaddle;

	if (ballHitBottomPaddle) {
	this.y_speed = randomOffset(-(Math.abs(paddleBottom.x_speed \|\| 4)), -0.9 * Math.abs(paddleBottom.x_speed \|\| 4));
	this.x_speed += (paddleBottom.x_speed / 2);
	this.y += this.y_speed;
	}
	}
	else {
	var topPaddleBottom = paddleTop.y + paddleTop.height;
	var ballTopIsOverTopPaddle = top_y < topPaddleBottom;
	var ballBottomIsUnderTopPaddle = bottom_y > paddleTop.y;

	var ballXOverlapsTopPaddle = top_x < (paddleTop.x + paddleTop.width) && bottom_x > paddleTop.x;

	var ballHitTopPaddle = ballTopIsOverTopPaddle && ballBottomIsUnderTopPaddle && ballXOverlapsTopPaddle;

	if (ballHitTopPaddle) {
	this.y_speed = randomOffset(0.9 * Math.abs(paddleTop.x_speed \|\| 4), Math.abs(paddleTop.x_speed \|\| 4));
	this.x_speed += (paddleTop.x_speed / 2);
	this.y += this.y_speed;
	}
	}

	};


	/**
	* Play some pong.
	* @param string appendToElementId The id of the element you want to put pong inside.
	* @param object window
	* @param object document
	* @returns HTML5CanvasElement The canvas inside the element for which you supplied the id.
	*/
	function Pong(appendToElementId, window, document) {

	var el = document.getElementById(appendToElementId);
	var animate = window.requestAnimationFrame \|\| window.webkitRequestAnimationFrame \|\| window.mozRequestAnimationFrame \|\| function (callback) {
	window.setTimeout(callback, 1000 / 60);
	};

	var canvas = document.createElement("canvas");
	canvas.width = WIDTH;
	canvas.height = HEIGHT;
	canvas.style.borderRadius = '5px';
	canvas.style.border = '2px solid ' + OFFWHITE;

	var context = canvas.getContext('2d');
	context.fillStyle = BLUE;
	context.font = "12px sans-serif";

	var player = new Player();
	var computer = new Computer();

	var ball = new Ball();

	var keysDown = {};


	function render() {
	context.fillStyle = OFFWHITE;
	context.fillRect(0, 0, canvas.width, canvas.height);
	context.fillStyle = BLUE;

	player.render(context);
	computer.render(context);
	ball.render(context);
	}

	function update() {
	player.update(keysDown);
	computer.update(ball);
	ball.update(player, computer);
	}

	function step() {
	update();
	render(context);
	animate(step);
	}


	el.appendChild(canvas);
	animate(step);

	var keydownEvent = function (event) {
	keysDown[event.keyCode] = true;
	};
	var keyupEvent = function (event) {
	delete keysDown[event.keyCode];
	};
	var elementDestroyed = function (event) {
	window.removeEventListener('keydown', keydownEvent, false);
	window.removeEventListener('keyup', keyupEvent, false);
	window.removeEventListener('DOMNodeRemoved', elementDestroyed, false);
	};

	window.addEventListener("keydown", keydownEvent);
	window.addEventListener("keyup", keyupEvent);
	window.addEventListener("DOMNodeRemoved", elementDestroyed);

	return el;
	};