代码之家 › 专栏 › 技术社区 › fightstarr20

drawImage-调整大小并保持比例

drawimage css html javascript

0

fightstarr20 · 技术社区 · 7 年前

window.onload = function() {
    var c = document.getElementById("myCanvas");
    var ctx = c.getContext("2d");
    var img = document.getElementById("scream");
    ctx.drawImage(img, 0, 0, 600, 428);
}

<p>Image to use:</p>
<img id="scream" width="400" height="300" src="http://lorempixel.com/1280/960/sports/" alt="The Scream">

<p>Canvas:</p>
<canvas id="myCanvas" width="428" height="600" style="border:2px solid black;">
Your browser does not support the HTML5 canvas tag.
</canvas>

我试图让图像填充容器,以丢失底部的空白,如果我放入精确的尺寸,那么它就会被拉伸。

有没有人能给我举个例子?

1 回复 | 直到 7 年前

1

3

philipp 7 年前

首先,您需要找到图像和画布的纵横比。这是由以下人员完成的:

var canvasRatio = canvas.width / canvas.height,
    imgRatio = img.width / img.height,
    s = 1;

然后你需要像这样比较这些比率:

//the image is Â»more portraitÂ«
//to fully cover the canvas
//scale by width
if (imgRatio < canvasRatio) {
  s = canvas.width / img.width;

//image has the same, or a Â»more landscapeÂ«
//ratio than the canvas
//to cover scale by height
} else {
  s = canvas.height / img.height;
}

//scale the context
ctx.scale(s, s);
cts.drawImage(â¦);

更新

if ):

var s = Math.max(canvas.width/img.width, canvas.height/img.height);

Math.min