Question

你好我有问题我尝试在50px x 50px画布上使用drawImage函数50px x 50px在画布上绘制图像，但是我比我需要的要小。

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.onload = function() {
    $("canvas").css("width", 50);
    $("canvas").css("height", 50);
    ctx.drawImage(img, 0, 0, 50, 50); //bad here why not drawing 50x50px image on the canvas?           
}
img.src = 'http://www.w3schools.com/tags/planets.gif';

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px">
<canvas id="canvas" style="position: absolute; top: 0px; left: 120px; border: 1px solid #000"></canvas>

Answer 1

不要通过CSS设置画布的宽度和高度。这将拉伸/压缩实际画布，缩放内容。

请改用旧的HTML width和height属性：

＆＃13;

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.onload = function() {
    ctx.drawImage(img, 0, 0, 50, 50);
}
img.src = 'http://www.w3schools.com/tags/planets.gif';

＆＃13;

<img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px">
<canvas
    id="canvas"
    style="position: absolute; top: 0px; left: 120px; border: 1px solid #000"
    width="50"
    height="50">
</canvas>

＆＃13;

这些属性实际上会改变画布的上下文宽度和高度，从而使图像的大小与您期望的大小完全相同。

HTML5画布drawImage图像大小不正确

1 个答案: