Question

嘿，我正在尝试使用setInterval每70毫秒在画布上绘制一个正方形。间隔设置为调用function draw()，此函数内部具有fillRect（）方法。但是我无法使它发挥任何作用吗？哦，我尝试了clearRect（），但是没有用。

//declare global variables
const canvas = document.querySelector('#canvas');

//set canvas context
const ctx = canvas.getContext('2d');

//put canvas dimensions into variables
const cvsW = canvas.width;
const cvsH = canvas.height;

//create snake unit
const unit = 16;

//create snake and set starting position
let snake = [{
	x : cvsW/2,
	y : cvsH/2
}]

//create a variable to store the direction of the snake
let direction;

//add event to read users input then change direction
document.addEventListener('keydown', (e) => {
	if(e.keycode == 37 && direction != 'right') direction = 'left';
	else if (e.keycode == 38 && direction != 'down') direction = 'up';
	else if (e.keycode == 39 && direction != 'left') direction = 'right';
	else if (e.keycode == 38 && direction != 'up') direction = 'down';
})

//move snake in chosen direction
if(direction == 'left') snake[0].x -= unit;
else if(direction == 'right') snake[0].x += unit;
else if(direction == 'up') snake[0].y -= unit;
else if(direction == 'down') snake[0].y += unit;

function draw() {
	ctx.fillStyle = 'limegreen';
	ctx.fillRect(snake[0].x - unit/2, snake[0].y - unit/2, unit, unit);
}


setInterval(70, draw);

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Snake</title>
	<style>
		body {
			background-color: #333;
		}

		#canvas {
			background-color: #4d4d4d;
			display: block;
			margin: auto;
			position: absolute;
			left: 0;
			top: 0;
			right: 0;
			bottom: 0;
		}
	</style>
</head>
<body>
	<canvas id="canvas" width="768" height="512"></canvas>
	<script src="script.js"></script>
</body>
</html>

Answer 1

您的代码中存在一些错误，但是我认为这就是您的意思：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Snake</title>
    <style>
        body {
            background-color: #333;
        }

        #canvas {
            background-color: #4d4d4d;
            display: block;
            margin: auto;
            position: absolute;
            left: 0;
            top: 0;
            right: 0;
            bottom: 0;
        }
    </style>
</head>
<body>
    <canvas id="canvas" width="768" height="512"></canvas>
    <script>
        //declare global variables
        const canvas = document.querySelector('#canvas');

        //set canvas context
        const ctx = canvas.getContext('2d');

        //put canvas dimensions into variables
        const cvsW = canvas.width;
        const cvsH = canvas.height;

        //create snake unit
        const unit = 16;

        //create snake and set starting position
        let snake = [{
            x : cvsW/2,
            y : cvsH/2
        }]

        //create a variable to store the direction of the snake
        let direction;

        //add event to read users input then change direction
        document.addEventListener('keydown', (e) => {
            if (e.keyCode == 37 && direction != 'right') direction = 'left';
            else if (e.keyCode == 38 && direction != 'down') direction = 'up';
            else if (e.keyCode == 39 && direction != 'left') direction = 'right';
            else if (e.keyCode == 40 && direction != 'up') direction = 'down';

            //move snake in chosen direction
            if (direction == 'left') snake[0].x -= unit;
            else if (direction == 'right') snake[0].x += unit;
            else if (direction == 'up') snake[0].y -= unit;
            else if (direction == 'down') snake[0].y += unit;

            console.log(e.keyCode, direction);
        })

        function draw() {
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            ctx.fillStyle = 'limegreen';
            ctx.fillRect(snake[0].x - unit/2, snake[0].y - unit/2, unit, unit);
            console.log('oi');
        }


        setInterval(draw, 70);
    </script>
</body>
</html>

请注意：

setInterval的参数顺序
大小写敏感度event.keyCode

无法使用setInterval在画布上绘制正方形？

1 个答案: