|
<!DOCTYPE html> |
|
<html> |
|
<head> |
|
<title>Basic Snake HTML Game</title> |
|
<meta charset="UTF-8"> |
|
<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'); |
|
|
|
// the canvas width & height, snake x & y, and the apple x & y, all need to be a multiples of the grid size in order for collision detection to work |
|
// (e.g. 16 * 25 = 400) |
|
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> |
@lemonadeblast125 Are there any JavaScript errors in the DevTools console? context.arc takes different numbers than context.fillRect.