如何自动缩放HTML5 <canvas>元素以适应页面?

例如,我可以得到一个<div>通过设置高度和宽度属性为100%缩放,但一个<canvas>不会缩放,会吗?


当前回答

一个纯CSS的方法添加到解决方案@jerseyboy上面。 适用于Firefox (v29测试),Chrome (v34测试)和Internet Explorer (v11测试)。

<!DOCTYPE html>
<html>
    <head>
    <style>
        html,
        body {
            width: 100%;
            height: 100%;
            margin: 0;
        }
        canvas {
            background-color: #ccc;
            display: block;
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            width: 100%;
            height: 100%;
        }
    </style>
</head>
<body>
    <canvas id="canvas" width="500" height="500"></canvas>
    <script>
        var canvas = document.getElementById('canvas');
        if (canvas.getContext) {
            var ctx = canvas.getContext('2d');
            ctx.fillRect(25,25,100,100);
            ctx.clearRect(45,45,60,60);
            ctx.strokeRect(50,50,50,50);
        }
    </script>
</body>
</html>

链接到示例:http://temporaer.net/open/so/140502_canvas-fit-to-window.html

但要小心,正如@jerseyboy在他的评论中所说:

用CSS重新缩放画布是很麻烦的。至少在Chrome和 Safari中,鼠标/触摸事件的位置不会1:1对应 Canvas像素位置,你需要变换坐标 系统。

其他回答

下面的解决方案对我来说效果最好。因为我对编码相对陌生,所以我喜欢用视觉来确认某些东西是否按照我期望的方式工作。我在以下地点找到了它: http://htmlcheats.com/html/resize-the-html5-canvas-dyamically/

代码如下:

(function() { var // Obtain a reference to the canvas element using its id. htmlCanvas = document.getElementById('c'), // Obtain a graphics context on the canvas element for drawing. context = htmlCanvas.getContext('2d'); // Start listening to resize events and draw canvas. initialize(); function initialize() { // Register an event listener to call the resizeCanvas() function // each time the window is resized. window.addEventListener('resize', resizeCanvas, false); // Draw canvas border for the first time. resizeCanvas(); } // Display custom canvas. In this case it's a blue, 5 pixel // border that resizes along with the browser window. function redraw() { context.strokeStyle = 'blue'; context.lineWidth = '5'; context.strokeRect(0, 0, window.innerWidth, window.innerHeight); } // Runs each time the DOM window resize event fires. // Resets the canvas dimensions to match window, // then draws the new borders accordingly. function resizeCanvas() { htmlCanvas.width = window.innerWidth; htmlCanvas.height = window.innerHeight; redraw(); } })(); html, body { width: 100%; height: 100%; margin: 0px; border: 0; overflow: hidden; /* Disable scrollbars */ display: block; /* No floating content on sides */ } <canvas id='c' style='position:absolute; left:0px; top:0px;'></canvas>

蓝色边框显示了调整画布的边缘,并且总是沿着窗口的边缘,在所有4个面都可见,这不是上述其他一些答案的情况。希望能有所帮助。

下面是一个小而完整的代码片段,它结合了所有的答案。按:“运行代码片段”,然后按“完整页面”,调整窗口大小,以查看其运行情况:

function refresh(referenceWidth, referenceHeight, drawFunction) { const myCanvas = document.getElementById("myCanvas"); myCanvas.width = myCanvas.clientWidth; myCanvas.height = myCanvas.clientHeight; const ratio = Math.min( myCanvas.width / referenceWidth, myCanvas.height / referenceHeight ); const ctx = myCanvas.getContext("2d"); ctx.scale(ratio, ratio); drawFunction(ctx, ratio); window.requestAnimationFrame(() => { refresh(referenceWidth, referenceHeight, drawFunction); }); } //100, 100 is the "reference" size. Choose whatever you want. refresh(100, 100, (ctx, ratio) => { //Custom drawing code! Draw whatever you want here. const referenceLineWidth = 1; ctx.lineWidth = referenceLineWidth / ratio; ctx.beginPath(); ctx.strokeStyle = "blue"; ctx.arc(50, 50, 49, 0, 2 * Math.PI); ctx.stroke(); }); div { width: 90vw; height: 90vh; } canvas { width: 100%; height: 100%; object-fit: contain; } <div> <canvas id="myCanvas"></canvas> </div>

这个片段使用画布。clientWidth和canvas。clientHeight而不是window。innerWidth和window。innerHeight使代码段在复杂布局中正确运行。然而,如果你只是把它放在一个使用全窗口的div中,它也适用于全窗口。这样更灵活。

代码片段使用了新窗口。请求animationframe重复调整画布的大小每帧。如果不能使用此方法,请使用setTimeout代替。而且,这是低效的。为了提高效率,存储clientWidth和clienttheight,只有当clientWidth和clienttheight改变时才重新计算和绘制。

“参考”分辨率的想法让你可以使用一个分辨率编写所有的绘制命令……并且它会自动调整到客户端大小,而无需更改绘图代码。

这个片段是不言自明的,但如果你喜欢用英语解释:https://medium.com/@doomgoober/resizing-canvas-vector-graphics- with-aliasing -7a1f9e684e4d

2022的答案

在2022年,检查元素是否调整大小的推荐方法是使用ResizeObserver

const observer = new ResizeObserver(myResizeTheCanvasFn);
observer.observe(someCanvasElement);

它比窗户好。addEventListener('resize', myResizeTheCanvasFn)或onresize = myResizeTheCanvasFn,因为它处理画布调整大小的每一种情况,即使它与窗口调整大小无关。

同样,使用window也没有意义。innerWidth window.innerHeight。你想要画布本身的大小,而不是窗口的大小。这样,无论你把画布放在哪里,你都会得到正确的大小,而不必重写你的尺寸代码。

至于用画布填满窗户

html, body {
  height: 100%;
}
canvas {
  width: 100%;
  height: 100%;
  display: block;   /* this is IMPORTANT! */
}

你需要display: block的原因是因为默认情况下画布是内联的,这意味着它在结尾包含额外的空间。没有显示:块你将得到一个滚动条。许多人通过在文档正文中添加overflow: hidden来修复滚动条问题,但这只是隐藏了画布的CSS设置不正确的事实。最好是修复bug(将canvas设置为display: block而不是使用overflow: hidden隐藏bug)

完整的示例

const canvas = document.querySelector('canvas'); const ctx = canvas.getContext('2d'); const observer = new ResizeObserver((entries) => { canvas.width = canvas.clientWidth; canvas.height = canvas.clientHeight; }); observer.observe(canvas) // not import but draw something just to showcase const hsla = (h, s, l, a) => `hsla(${h * 360}, ${s * 100}%, ${l * 100}%, ${a})`; function render(time) { const {width, height} = canvas; ctx.clearRect(0, 0, width, height); ctx.save(); ctx.translate(width / 2, height / 2); ctx.rotate(time * 0.0001); const range = Math.max(width, height) * 0.8; const size = 64 + Math.sin(time * 0.001) * 50; for (let i = 0; i < range; i += size) { ctx.fillStyle = hsla(i / range * 0.3 + time * 0.0001, 1, 0.5, 1); ctx.fillRect( i, -range, size, range * 2); ctx.fillRect(-i, -range, size, range * 2); } ctx.restore(); requestAnimationFrame(render) } requestAnimationFrame(render) html, body { height: 100%; margin: 0; } canvas { width: 100%; height: 100%; display: block; } <canvas></canvas>

注意:还有其他与调整画布大小相关的问题。特别是如果你想处理不同的devicePixelRatio设置。请参阅本文了解更多信息。

基本上你要做的是将onresize事件绑定到你的body,一旦你捕捉到事件,你只需要使用window调整画布的大小。innerWidth和window.innerHeight。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Canvas Resize</title>

    <script type="text/javascript">
        function resize_canvas(){
            canvas = document.getElementById("canvas");
            if (canvas.width  < window.innerWidth)
            {
                canvas.width  = window.innerWidth;
            }

            if (canvas.height < window.innerHeight)
            {
                canvas.height = window.innerHeight;
            }
        }
    </script>
</head>

<body onresize="resize_canvas()">
        <canvas id="canvas">Your browser doesn't support canvas</canvas>
</body>
</html>
(function() {

    // get viewport size
    getViewportSize = function() {
        return {
            height: window.innerHeight,
            width:  window.innerWidth
        };
    };

    // update canvas size
    updateSizes = function() {
        var viewportSize = getViewportSize();
        $('#myCanvas').width(viewportSize.width).height(viewportSize.height);
        $('#myCanvas').attr('width', viewportSize.width).attr('height', viewportSize.height);
    };

    // run on load
    updateSizes();

    // handle window resizing
    $(window).on('resize', function() {
        updateSizes();
    });

}());