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<!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> |
