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WindRunnerMax committed Aug 11, 2023
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6 changes: 6 additions & 0 deletions CATALOG.md
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# Catalog

**2023-08-11**
> 第403题：[SVG与foreignObject元素](HTML/SVG与foreignObject元素.md)
<br>


**2023-07-16**
> 第402题：[从零实现的Chrome扩展](Plugin/从零实现的Chrome扩展.md)
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180 changes: 179 additions & 1 deletion HTML/SVG与foreignObject元素.md
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```

```xml
<svg xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="263px" height="103px" viewBox="-0.5 -0.5 263 103"><defs></defs><g><rect x="1" y="1" width="260" height="100" fill="#ffffff" stroke="#000000" pointer-events="all"></rect><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 258px; height: 1px; padding-top: 51px; margin-left: 2px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; "><div><span>This is a long text that will automatically wrap within the rectangle.</span></div></div></div></div></foreignObject><text x="131" y="55" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">This is a long text that will automatically...</text></switch></g></g><switch><g requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"></g><a transform="translate(0,-5)" xlink:href="https://desk.draw.io/support/solutions/articles/16000042487" target="_blank"><text text-anchor="middle" font-size="10px" x="50%" y="100%">Viewer does not support full SVG 1.1</text></a></switch></svg>
<svg
xmlns:xlink="http://www.w3.org/1999/xlink"
version="1.1"
width="263px"
height="103px"
viewBox="-0.5 -0.5 263 103"
>
<defs></defs>
<g>
<rect
x="1"
y="1"
width="260"
height="100"
fill="#ffffff"
stroke="#000000"
pointer-events="all"
></rect>
<g transform="translate(-0.5 -0.5)">
<switch>
<foreignObject
style="overflow: visible; text-align: left;"
pointer-events="none"
width="100%"
height="100%"
requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"
>
<div style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 258px; height: 1px; padding-top: 51px; margin-left: 2px;">
<div style="box-sizing: border-box; font-size: 0; text-align: center; ">
<div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">
<div>
<span>
This is a long text that will automatically wrap within the rectangle.
</span>
</div>
</div>
</div>
</div>
</foreignObject>
<text
x="131"
y="55"
fill="#000000"
font-family="Helvetica"
font-size="12px"
text-anchor="middle"
>
This is a long text that will automatically...
</text>
</switch>
</g>
</g>
<switch>
<g requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"></g>
<a
transform="translate(0,-5)"
xlink:href="https://desk.draw.io/support/solutions/articles/16000042487"
target="_blank"
>
<text text-anchor="middle" font-size="10px" x="50%" y="100%">
Viewer does not support full SVG 1.1
</text>
</a>
</switch>
</svg>
```

看起来一切都很完美，我们既能够借助`SVG`绘制矢量图形，又能够在比较复杂的情况下借助`HTML`的能力完成需求，但是事情总有两面性，当我们在某一方面享受到便利的时候，就可能在另一处带来意想不到的麻烦。设想一个场景，假设此时我们需要在后端将`SVG`绘制出来，然后将其转换为`PNG`格式的图片给予用户下载，在前端做一些批量的操作是不太现实的，再假设我们需要将这个`SVG`绘制出来拼接到`Word`或者`Excel`中，那么这些操作都要求我们需要在后端完整地将整个图片绘制出来，那么此时我们可能会想到`node-canvas`在后端创建和操作图形，但是当我们真的使用`node-canvas`绘制我们的`SVG`图形时例如上边的`DrawIO`的例子，会发现所有的图形形状是可以被绘制出来的，但是所有的文本都丢失了，那么既然`node-canvas`做不到，那么我们可能会想到`sharp`来完成图像处理的相关功能，例如先将`SVG`转换为`PNG`，但是很遗憾的是`sharp`也做不到这一点，最终效果与`node-canvas`是一致的。
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```

## DOM TO IMAGE
让我们想一想，`foreignObject`元素看起来是个非常神奇的设计，通过`foreignObject`元素我们可以把`HTML`绘制到`SVG`当中，那么我们是不是可以有一个非常神奇的点子，如果我们此时需要将浏览器当中的`DOM`绘制出来，实现于类似于截图的效果，那么我我们是不是就可以借助`foreignObject`元素来实现呢。这当然是可行的，而且是一件非常有意思的事情，我们可以将`DOM + CSS`绘制到`SVG`当中，紧接着将其转换为`DATA URL`，借助`canvas`将其绘制出来，最终我们就可以将`DOM`生成图像以及导出了。

下面就是个这个能力的实现，当然在这里的实现还是比较简单的，主要处理的部分就是将`DOM`进行`clone`以及样式全部内联，由此来生成完整的`SVG`图像。实际上这其中还有很多需要注意的地方，例如生成伪元素、`@font-face`字体的声明、`BASE64`编码的内容、`img`元素到`CSS background`属性的转换等等，想要比较完整地实现整个功能还是需要考虑到很多`case`的，在这里就不涉及具体的实现了，可以参考`dom-to-image-more`。

```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>DOM IMAGE</title>
<style>
#root {
width: 300px;
border: 1px solid #eee;
}
.list > .list-item {
display: flex;
background-color: #aaa;
color: #fff;
align-items: center;
justify-content: space-between;
}
</style>
</head>
<body>
<!-- #root START -->
<!-- `DOM`内容-->
<div id="root">
<h1>Title</h1>
<hr />
<div>Content</div>
<div class="list">
<div class="list-item">
<span>label</span>
<span>value</span>
</div>
<div class="list-item">
<span>label</span>
<span>value</span>
</div>
</div>
</div>
<!-- #root END -->
<button onclick="onDOMToImage()">下载</button>
</body>
<script>
const cloneCSS = (target, origin) => {
const style = window.getComputedStyle(origin);
// 生成所有样式表
const cssText = Array.from(style).reduce((acc, key) => {
return `${acc}${key}:${style.getPropertyValue(key)};`;
}, "");
target.style.cssText = cssText;
};
const cloneDOM = (origin) => {
const target = origin.cloneNode(true);
const targetNodes = target.querySelectorAll("*");
const originNodes = origin.querySelectorAll("*");
// 复制根节点样式
cloneCSS(target, origin);
// 复制所有节点样式
Array.from(targetNodes).forEach((node, index) => {
cloneCSS(node, originNodes[index]);
});
// 去除元素的外边距
target.style.margin =
target.style.marginLeft =
target.style.marginTop =
target.style.marginBottom =
target.style.marginRight =
"";
return target;
};
const buildSVGUrl = (node, width, height) => {
const xml = new XMLSerializer().serializeToString(node);
const data = `
<svg xmlns="http://www.w3.org/2000/svg" width="${width}" height="${height}">
<foreignObject width="100%" height="100%">
${xml}
</foreignObject>
</svg>
`;
return "data:image/svg+xml;charset=utf-8," + encodeURIComponent(data);
};
const onDOMToImage = () => {
const origin = document.getElementById("root");
const { width, height } = root.getBoundingClientRect();
const target = cloneDOM(origin);
const data = buildSVGUrl(target, width, height);
const image = new Image();
image.crossOrigin = "anonymous";
image.src = data;
image.onload = () => {
const canvas = document.createElement("canvas");
// 值越大像素越高
const ratio = window.devicePixelRatio || 1;
canvas.width = width * ratio;
canvas.height = height * ratio;
const ctx = canvas.getContext("2d");
ctx.scale(ratio, ratio);
ctx.drawImage(image, 0, 0);
const a = document.createElement("a");
a.href = canvas.toDataURL("image/png");
a.download = "image.png";
a.click();
};
};
</script>
</html>
```

## 每日一题

Expand All @@ -153,6 +330,7 @@ https://github.com/WindrunnerMax/EveryDay
https://github.com/jgraph/drawio
https://github.com/pbakaus/domvas
https://github.com/puppeteer/puppeteer
https://www.npmjs.com/package/dom-to-image-more
https://developer.mozilla.org/zh-CN/docs/Web/SVG
https://zzerd.com/blog/2021/04/10/linux/debian_install_puppeteer
https://developer.mozilla.org/zh-CN/docs/Web/SVG/Element/foreignObject
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1 change: 1 addition & 0 deletions README.md
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* [Shadow DOM的理解](HTML/Shadow%20DOM的理解.md)
* [Service Worker的应用](HTML/Service%20Worker的应用.md)
* [蒙层禁止页面滚动的方案](HTML/蒙层禁止页面滚动的方案.md)
* [SVG与foreignObject元素](HTML/SVG与foreignObject元素.md)

## CSS
* [布局垂直居中](CSS/布局垂直居中.md)
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