169 lines
4.0 KiB
HTML
169 lines
4.0 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<title></title>
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<style>
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html, body {
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height: 100%;
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margin: 0;
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}
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body {
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background: black;
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display: flex;
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align-items: center;
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justify-content: center;
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}
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canvas {
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border: 1px solid white;
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}
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</style>
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</head>
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<body>
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<canvas width="400" height="400" id="game"></canvas>
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<script>
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var canvas = document.getElementById('game');
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var context = canvas.getContext('2d');
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var grid = 16;
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var count = 0;
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var snake = {
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x: 160,
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y: 160,
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// snake velocity. moves one grid length every frame in either the x or y direction
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dx: grid,
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dy: 0,
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// keep track of all grids the snake body occupies
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cells: [],
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// length of the snake. grows when eating an apple
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maxCells: 4
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};
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var apple = {
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x: 320,
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y: 320
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};
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// get random whole numbers in a specific range
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// @see https://stackoverflow.com/a/1527820/2124254
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function getRandomInt(min, max) {
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return Math.floor(Math.random() * (max - min)) + min;
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}
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// game loop
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function loop() {
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requestAnimationFrame(loop);
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// slow game loop to 15 fps instead of 60 (60/15 = 4)
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if (++count < 4) {
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return;
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}
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count = 0;
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context.clearRect(0,0,canvas.width,canvas.height);
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// move snake by it's velocity
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snake.x += snake.dx;
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snake.y += snake.dy;
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// wrap snake position horizontally on edge of screen
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if (snake.x < 0) {
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snake.x = canvas.width - grid;
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}
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else if (snake.x >= canvas.width) {
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snake.x = 0;
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}
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// wrap snake position vertically on edge of screen
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if (snake.y < 0) {
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snake.y = canvas.height - grid;
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}
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else if (snake.y >= canvas.height) {
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snake.y = 0;
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}
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// keep track of where snake has been. front of the array is always the head
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snake.cells.unshift({x: snake.x, y: snake.y});
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// remove cells as we move away from them
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if (snake.cells.length > snake.maxCells) {
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snake.cells.pop();
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}
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// draw apple
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context.fillStyle = 'red';
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context.fillRect(apple.x, apple.y, grid-1, grid-1);
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// draw snake one cell at a time
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context.fillStyle = 'green';
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snake.cells.forEach(function(cell, index) {
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// drawing 1 px smaller than the grid creates a grid effect in the snake body so you can see how long it is
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context.fillRect(cell.x, cell.y, grid-1, grid-1);
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// snake ate apple
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if (cell.x === apple.x && cell.y === apple.y) {
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snake.maxCells++;
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// canvas is 400x400 which is 25x25 grids
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apple.x = getRandomInt(0, 25) * grid;
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apple.y = getRandomInt(0, 25) * grid;
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}
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// check collision with all cells after this one (modified bubble sort)
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for (var i = index + 1; i < snake.cells.length; i++) {
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// snake occupies same space as a body part. reset game
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if (cell.x === snake.cells[i].x && cell.y === snake.cells[i].y) {
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snake.x = 160;
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snake.y = 160;
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snake.cells = [];
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snake.maxCells = 4;
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snake.dx = grid;
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snake.dy = 0;
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apple.x = getRandomInt(0, 25) * grid;
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apple.y = getRandomInt(0, 25) * grid;
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}
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}
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});
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}
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// listen to keyboard events to move the snake
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document.addEventListener('keydown', function(e) {
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// prevent snake from backtracking on itself by checking that it's
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// not already moving on the same axis (pressing left while moving
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// left won't do anything, and pressing right while moving left
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// shouldn't let you collide with your own body)
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// left arrow key
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if (e.which === 37 && snake.dx === 0) {
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snake.dx = -grid;
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snake.dy = 0;
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}
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// up arrow key
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else if (e.which === 38 && snake.dy === 0) {
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snake.dy = -grid;
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snake.dx = 0;
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}
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// right arrow key
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else if (e.which === 39 && snake.dx === 0) {
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snake.dx = grid;
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snake.dy = 0;
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}
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// down arrow key
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else if (e.which === 40 && snake.dy === 0) {
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snake.dy = grid;
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snake.dx = 0;
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}
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});
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// start the game
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requestAnimationFrame(loop);
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</script>
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</body>
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</html>
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