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December 4, 2018 07:01
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Many WEB DEVELOPMENT beginners struggle writing the snake game code. The game consists on guiding a snake to eat its food, avoid the snake's head touching any part of its own body . As much as the snake eats the food, it gets bigger. The code is easy and it is not big. Here I will share the game code for who wants to learn more about the code. I…
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<!DOCTYPE html> | |
<html> | |
<head> | |
<title></title> | |
<style> | |
html, body { | |
height: 100%; | |
margin: 0; | |
} | |
body { | |
background: black; | |
display: flex; | |
align-items: center; | |
justify-content: center; | |
} | |
canvas { | |
border: 1px solid white; | |
} | |
</style> | |
</head> | |
<body> | |
<canvas width="400" height="400" id="game"></canvas> | |
<script> | |
var canvas = document.getElementById('game'); | |
var context = canvas.getContext('2d'); | |
var grid = 16; | |
var count = 0; | |
var snake = { | |
x: 160, | |
y: 160, | |
// snake velocity. moves one grid length every frame in either the x or y direction | |
dx: grid, | |
dy: 0, | |
// keep track of all grids the snake body occupies | |
cells: [], | |
// length of the snake. grows when eating an apple | |
maxCells: 4 | |
}; | |
var apple = { | |
x: 320, | |
y: 320 | |
}; | |
// get random whole numbers in a specific range | |
// @see https://stackoverflow.com/a/1527820/2124254 | |
function getRandomInt(min, max) { | |
return Math.floor(Math.random() * (max - min)) + min; | |
} | |
// game loop | |
function loop() { | |
requestAnimationFrame(loop); | |
// slow game loop to 15 fps instead of 60 (60/15 = 4) | |
if (++count < 4) { | |
return; | |
} | |
count = 0; | |
context.clearRect(0,0,canvas.width,canvas.height); | |
// move snake by it's velocity | |
snake.x += snake.dx; | |
snake.y += snake.dy; | |
// wrap snake position horizontally on edge of screen | |
if (snake.x < 0) { | |
snake.x = canvas.width - grid; | |
} | |
else if (snake.x >= canvas.width) { | |
snake.x = 0; | |
} | |
// wrap snake position vertically on edge of screen | |
if (snake.y < 0) { | |
snake.y = canvas.height - grid; | |
} | |
else if (snake.y >= canvas.height) { | |
snake.y = 0; | |
} | |
// keep track of where snake has been. front of the array is always the head | |
snake.cells.unshift({x: snake.x, y: snake.y}); | |
// remove cells as we move away from them | |
if (snake.cells.length > snake.maxCells) { | |
snake.cells.pop(); | |
} | |
// draw apple | |
context.fillStyle = 'red'; | |
context.fillRect(apple.x, apple.y, grid-1, grid-1); | |
// draw snake one cell at a time | |
context.fillStyle = 'green'; | |
snake.cells.forEach(function(cell, index) { | |
// drawing 1 px smaller than the grid creates a grid effect in the snake body so you can see how long it is | |
context.fillRect(cell.x, cell.y, grid-1, grid-1); | |
// snake ate apple | |
if (cell.x === apple.x && cell.y === apple.y) { | |
snake.maxCells++; | |
// canvas is 400x400 which is 25x25 grids | |
apple.x = getRandomInt(0, 25) * grid; | |
apple.y = getRandomInt(0, 25) * grid; | |
} | |
// check collision with all cells after this one (modified bubble sort) | |
for (var i = index + 1; i < snake.cells.length; i++) { | |
// snake occupies same space as a body part. reset game | |
if (cell.x === snake.cells[i].x && cell.y === snake.cells[i].y) { | |
snake.x = 160; | |
snake.y = 160; | |
snake.cells = []; | |
snake.maxCells = 4; | |
snake.dx = grid; | |
snake.dy = 0; | |
apple.x = getRandomInt(0, 25) * grid; | |
apple.y = getRandomInt(0, 25) * grid; | |
} | |
} | |
}); | |
} | |
// listen to keyboard events to move the snake | |
document.addEventListener('keydown', function(e) { | |
// prevent snake from backtracking on itself by checking that it's | |
// not already moving on the same axis (pressing left while moving | |
// left won't do anything, and pressing right while moving left | |
// shouldn't let you collide with your own body) | |
// left arrow key | |
if (e.which === 37 && snake.dx === 0) { | |
snake.dx = -grid; | |
snake.dy = 0; | |
} | |
// up arrow key | |
else if (e.which === 38 && snake.dy === 0) { | |
snake.dy = -grid; | |
snake.dx = 0; | |
} | |
// right arrow key | |
else if (e.which === 39 && snake.dx === 0) { | |
snake.dx = grid; | |
snake.dy = 0; | |
} | |
// down arrow key | |
else if (e.which === 40 && snake.dy === 0) { | |
snake.dy = grid; | |
snake.dx = 0; | |
} | |
}); | |
// start the game | |
requestAnimationFrame(loop); | |
</script> | |
</body> | |
</html> |
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