无法使用setInterval在画布上绘制正方形？

Question

Hey Guys I'm trying to draw a square to the canvas every 70ms using setInterval. 嗨，我正在尝试使用setInterval每70毫秒在画布上绘制一个正方形。 The Interval is set to call function draw() this function has the fillRect() method inside it. Interval设置为调用function draw()此函数内部具有fillRect（）方法。 But I can't get it to work any ideas? 但是我无法使它发挥任何作用吗？ Oh and I tried clearRect() and that didn't work. 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

There were some bugs in your code, but I think this is what you meant: 您的代码中存在一些错误，但是我认为这是您的意思：

<!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>

Please notice: 请注意：

Argument order of setInterval setInterval参数顺序
Case sensitivity of event.keyCode event.keyCode区分大小写

无法使用setInterval在画布上绘制正方形？

问题描述

1 个解决方案

解决方案1
0 已采纳 2019-01-20 03:07:57

无法使用setInterval在画布上绘制正方形？

问题描述

1 个解决方案

解决方案1 0 已采纳 2019-01-20 03:07:57

解决方案1
0 已采纳 2019-01-20 03:07:57