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index.html
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<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Ping Pong</title>
<link rel="icon" href="https://i.imgur.com/fjRzbpH.png">
<!-- Basic styling, centering the canvas -->
<style>
canvas {
display: block;
position: absolute;
margin: auto;
top: 0;
bottom: 0;
left: 0;
right: 0;
}
</style>
</head>
<body>
<script>
var
/**
* Constants
*/
WIDTH = 1280,
HEIGHT = 720,
pi = Math.PI,
UpArrow = 38,
DownArrow = 40,
/**
* Game elements
*/
canvas,
ctx,
keystate,
/**
* The player paddle
*
* @type {Object}
*/
player = {
x: null,
y: null,
width: 20,
height: 100,
/**
* Update the position depending on pressed keys
*/
update: function() {
if (keystate[UpArrow]) this.y -= 7;
if (keystate[DownArrow]) this.y += 7;
// keep the paddle inside of the canvas
this.y = Math.max(Math.min(this.y, HEIGHT - this.height), 0);
},
/**
* Draw the player paddle to the canvas
*/
draw: function() {
ctx.fillRect(this.x, this.y, this.width, this.height);
}
},
/**
* The ai paddle
*
* @type {Object}
*/
ai = {
x: null,
y: null,
width: 20,
height: 100,
/**
* Update the position depending on the ball position
*/
update: function() {
// calculate ideal position
var desty = ball.y - (this.height - ball.side)*0.5;
// ease the movement towards the ideal position
this.y += (desty - this.y) * 0.1;
// keep the paddle inside of the canvas
this.y = Math.max(Math.min(this.y, HEIGHT - this.height), 0);
},
/**
* Draw the ai paddle to the canvas
*/
draw: function() {
ctx.fillRect(this.x, this.y, this.width, this.height);
}
},
/**
* The ball object
*
* @type {Object}
*/
ball = {
x: null,
y: null,
vel: null,
side: 20,
speed: 7,
/**
* Serves the ball towards the specified side
*
* @param {number} side 1 right
* -1 left
*/
serve: function(side) {
// set the x and y position
var r = Math.random();
this.x = side===1 ? player.x+player.width : ai.x - this.side;
this.y = (HEIGHT - this.side)*r;
// calculate out-angle, higher/lower on the y-axis =>
// steeper angle
var phi = 0.1*pi*(1 - 2*r);
// set velocity direction and magnitude
this.vel = {
x: side*this.speed*Math.cos(phi),
y: this.speed*Math.sin(phi)
}
},
/**
* Update the ball position and keep it within the canvas
*/
update: function() {
// update position with current velocity
this.x += this.vel.x;
this.y += this.vel.y;
// check if out of the canvas in the y direction
if (0 > this.y || this.y+this.side > HEIGHT) {
// calculate and add the right offset, i.e. how far
// inside of the canvas the ball is
var offset = this.vel.y < 0 ? 0 - this.y : HEIGHT - (this.y+this.side);
this.y += 2*offset;
// mirror the y velocity
this.vel.y *= -1;
}
// helper function to check intesectiont between two
// axis aligned bounding boxex (AABB)
var AABBIntersect = function(ax, ay, aw, ah, bx, by, bw, bh) {
return ax < bx+bw && ay < by+bh && bx < ax+aw && by < ay+ah;
};
// check againts target paddle to check collision in x
// direction
var pdle = this.vel.x < 0 ? player : ai;
if (AABBIntersect(pdle.x, pdle.y, pdle.width, pdle.height,
this.x, this.y, this.side, this.side)
) {
// set the x position and calculate reflection angle
this.x = pdle===player ? player.x+player.width : ai.x - this.side;
var n = (this.y+this.side - pdle.y)/(pdle.height+this.side);
var phi = 0.25*pi*(2*n - 1); // pi/4 = 45
// calculate smash value and update velocity
var smash = Math.abs(phi) > 0.2*pi ? 1.5 : 1;
this.vel.x = smash*(pdle===player ? 1 : -1)*this.speed*Math.cos(phi);
this.vel.y = smash*this.speed*Math.sin(phi);
}
// reset the ball when ball outside of the canvas in the
// x direction
if (0 > this.x+this.side || this.x > WIDTH) {
this.serve(pdle===player ? 1 : -1);
}
},
/**
* Draw the ball to the canvas
*/
draw: function() {
ctx.fillRect(this.x, this.y, this.side, this.side);
}
};
/**
* Starts the game
*/
function main() {
// create, initiate and append game canvas
canvas = document.createElement("canvas");
canvas.width = WIDTH;
canvas.height = HEIGHT;
ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
keystate = {};
// keep track of keyboard presses
document.addEventListener("keydown", function(evt) {
keystate[evt.keyCode] = true;
});
document.addEventListener("keyup", function(evt) {
delete keystate[evt.keyCode];
});
init(); // initiate game objects
// game loop function
var loop = function() {
update();
draw();
window.requestAnimationFrame(loop, canvas);
};
window.requestAnimationFrame(loop, canvas);
}
/**
* Initatite game objects and set start positions
*/
function init() {
player.x = player.width;
player.y = (HEIGHT - player.height)/2;
ai.x = WIDTH - (player.width + ai.width);
ai.y = (HEIGHT - ai.height)/2;
ball.serve(1);
}
/**
* Update all game objects
*/
function update() {
ball.update();
player.update();
ai.update();
}
/**
* Clear canvas and draw all game objects and net
*/
function draw() {
ctx.fillRect(0, 0, WIDTH, HEIGHT);
ctx.save();
ctx.fillStyle = "#fff";
ball.draw();
player.draw();
ai.draw();
// draw the net
var w = 4;
var x = (WIDTH - w)*0.5;
var y = 0;
var step = HEIGHT/20; // how many net segments
while (y < HEIGHT) {
ctx.fillRect(x, y+step*0.25, w, step*0.5);
y += step;
}
ctx.restore();
}
// start and run the game
main();
</script>
</body>
</html>