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snake.html
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<!doctype html>
<html>
<head>
<title>
Snake
</title>
<style type="text/css">
* {
background: black;
color: white;
font-family: Calibri;
font-size: 15px;
}
canvas {
border: 1px solid white;
}
</style>
<script type="text/javascript">
// canvas and context
var canvas = null;
var ctx = null;
// window variable
var width = 0;
var height = 0;
// game variable
var snakeSize = 10;
var snakeLength = 3;
var snakeScore = 0;
var gameRequireRestart = new Boolean();
// game timer variable
var level = 0;
var MAX_LEVEL = 10;
var countdown = 500;
var COUNTDOWN_UNIT = 50;
var DEFAULT_COUNTDOWN = 500;
var timer = null;
// snake variable
var heading = 6;
var HEADING_UP = 2;
var HEADING_RIGHT = 6;
var HEADING_DOWN = 9;
var HEADING_LEFT = 4;
var snakeLocation = null;
var oldSnakeLocation = null;
var snakeMoved = new Boolean();
var snakeFood = null;
function init() {
canvas = document.getElementById('snakeCanvas');
var canvasWidth = window.innerWidth;
var canvasHeight = window.innerHeight;
canvasWidth -= 30;
canvasHeight -= 110;
canvasWidth -= canvasWidth % snakeSize;
canvasHeight -= canvasHeight % snakeSize;
canvas.width = canvasWidth;
canvas.height = canvasHeight;
width = canvas.width;
height = canvas.height;
snakeLocation = new Array(snakeLength);
for (var i = 0; i < snakeLength; i++) {
snakeLocation[i] = new Array(2);
if (i == 0) {
snakeLocation[i][0] = (snakeLength - 2) * snakeSize;
snakeLocation[i][1] = Math.floor((height - snakeSize) / 2);
} else {
snakeLocation[i][0] = snakeLocation[i-1][0] - snakeSize;
snakeLocation[i][1] = snakeLocation[i-1][1];
}
snakeLocation[i][0] -= snakeLocation[i][0] % snakeSize;
snakeLocation[i][1] -= snakeLocation[i][1] % snakeSize;
}
if (canvas.getContext) {
ctx = canvas.getContext('2d');
generateFood();
drawFood();
draw();
}
}
function generateFood() {
snakeFood = new Array(2);
snakeFood[0] = Math.floor(Math.random() * width);
snakeFood[1] = Math.floor(Math.random() * height);
snakeFood[0] -= snakeFood[0] % snakeSize;
snakeFood[1] -= snakeFood[1] % snakeSize;
checkIfFoodOverlapSnake();
}
function checkIfFoodOverlapSnake() {
var overlap = new Boolean();
overlap = false;
if (oldSnakeLocation != null) {
for (var i = 0; i < snakeLength; i++) {
if (oldSnakeLocation[i] != null) {
if (snakeFood[0] == oldSnakeLocation[i][0]
&& snakeFood[1] == oldSnakeLocation[i][1]) {
overlap = true;
}
}
}
}
if (overlap) {
generateFood();
}
}
function drawFood() {
ctx.fillStyle = "rgb(0,0,255)";
ctx.fillRect(snakeFood[0], snakeFood[1], snakeSize, snakeSize);
}
function draw() {
clearRect();
calculateLocation();
drawRect();
startTimer();
if (gameRequireRestart) {
gameRequireRestart = false;
restartGame();
}
}
function clearRect() {
for (var i = 0; i < snakeLength; i++) {
ctx.clearRect(snakeLocation[i][0], snakeLocation[i][1], snakeSize, snakeSize);
}
}
function calculateLocation() {
oldSnakeLocation = snakeLocation;
snakeLocation = new Array(snakeLength);
snakeLocation[0] = new Array(2);
snakeLocation[0][0] = oldSnakeLocation[0][0];
snakeLocation[0][1] = oldSnakeLocation[0][1];
if (heading == HEADING_UP) {
snakeLocation[0][1] = snakeLocation[0][1] - snakeSize;
} else if (heading == HEADING_RIGHT) {
snakeLocation[0][0] = snakeLocation[0][0] + snakeSize;
} else if (heading == HEADING_DOWN) {
snakeLocation[0][1] = snakeLocation[0][1] + snakeSize;
} else if (heading == HEADING_LEFT) {
snakeLocation[0][0] = snakeLocation[0][0] - snakeSize;
}
detectIfCollideWithSnake();
detectIfReachedFood();
for (var i = 1; i < snakeLength; i++) {
snakeLocation[i] = oldSnakeLocation[i-1];
}
// filter out of bound
for (var i = 0; i < snakeLength; i++) {
if (snakeLocation[i][0] + snakeSize > width) {
snakeLocation[i][0] = 0;
}
if (snakeLocation[i][0] < 0) {
snakeLocation[i][0] = width - snakeSize;
/* to compensate for the size of the rectangle
if set to width, it will be not in the canvas, but outside */
}
if (snakeLocation[i][1] + snakeSize > height ) {
snakeLocation[i][1] = 0;
}
if (snakeLocation[i][1] < 0) {
snakeLocation[i][1] = height - snakeSize;
}
}
snakeMoved = true;
}
function detectIfCollideWithSnake() {
for (var i = 1; i < snakeLength; i++) {
if (snakeLocation[0][0] == oldSnakeLocation[i][0]
&& snakeLocation[0][1] == oldSnakeLocation[i][1]) {
gameRequireRestart = true;
}
}
}
function detectIfReachedFood() {
if (snakeLocation[0][0] == snakeFood[0]
&& snakeLocation[0][1] == snakeFood[1]) {
snakeLength++;
snakeScore += level + 1;
updateGameScore();
generateFood();
drawFood();
}
}
function updateGameScore() {
document.getElementById('score').innerHTML = snakeScore;
}
function drawRect() {
ctx.fillStyle = "rgb(255,0,0)";
for (var i = 0; i < snakeLength; i++) {
ctx.fillRect(snakeLocation[i][0], snakeLocation[i][1], snakeSize, snakeSize);
}
}
function startTimer() {
timer = setTimeout("draw()", countdown);
}
function restartGame() {
clearGameStatus();
init();
}
function clearGameStatus() {
clearTimeout(timer);
snakeLength = 3;
snakeScore = 0;
updateGameScore();
heading = 6;
level = 0;
updateGameLevel();
snakeLocation = null;
oldSnakeLocation = null;
}
function keyPressed(e) {
var key = e.keyCode;
if (key == 38 || key == 87) {
// up or W
changeDirection(HEADING_UP);
} else if (key == 39 || key == 68) {
// right or D
changeDirection(HEADING_RIGHT);
} else if (key == 40 || key == 83) {
// down or S
changeDirection(HEADING_DOWN);
} else if (key == 37 || key == 65) {
// left or A
changeDirection(HEADING_LEFT);
} else if (key == 82) {
// [R]estart
requestRestartGame();
} else if (key == 189) {
// -
decreaseGameSpeed();
} else if (key == 187) {
// +
increaseGameSpeed();
} else {
}
}
function changeDirection(newHeading) {
if (snakeMoved) {
if (newHeading == HEADING_UP) {
if (heading != HEADING_DOWN) {
heading = HEADING_UP;
}
} else if (newHeading == HEADING_RIGHT) {
if (heading != HEADING_LEFT) {
heading = HEADING_RIGHT;
}
} else if (newHeading == HEADING_DOWN) {
if (heading != HEADING_UP) {
heading = HEADING_DOWN;
}
} else if (newHeading == HEADING_LEFT) {
if (heading != HEADING_RIGHT) {
heading = HEADING_LEFT;
}
}
snakeMoved = false;
}
}
function increaseGameSpeed() {
// level 0 (500ms) ~ 9 (50ms)
if (level < MAX_LEVEL - 1) {
level++;
}
updateGameLevel();
}
function decreaseGameSpeed() {
if (level > 0) {
level--;
}
updateGameLevel();
}
function updateGameLevel() {
countdown = DEFAULT_COUNTDOWN - (level * COUNTDOWN_UNIT);
document.getElementById('level').innerHTML = level + 1;
}
function requestRestartGame() {
gameRequireRestart = true;
}
</script>
</head>
<header>
<table>
<tr>
<td>
<button onclick="requestRestartGame();">
Restart
</button>
</td>
<td>
|
</td>
<td>
Level:
</td>
<td id="level">
1
</td>
<td>
|
</td>
<td>
Score:
</td>
<td id="score">
0
</td>
</tr>
</table>
</header>
<body onload="init();" onkeyup="keyPressed(event)">
<canvas id="snakeCanvas">
</canvas>
</body>
<footer>
<p>
© Chua Jie Sheng | [email protected]
</p>
</footer>
</html>