<svg xmlns="http://www.w3.org/2000/svg" id="svg" width="512" height="512" viewBox="0 0 8 8">
    <defs>
        <path id="a" d="M1,1 2,1 2,4 1,4 z" />
    </defs>
    <clipPath id="s">
        <use xlink:href="#a" />
    </clipPath>
    <g clip-path="url(#s)">
        <rect x="0" y="1" width="3" height="2" />
    </g>
</svg>

当存在 xlink:href 属性时，必须在 <svg> 中添加 xmlns:xlink="http://www.w3.org/1999/xlink"

当前生成的 PNG 效果如下图：

期望其最终效果是宽度填满，高度等比缩放。也就是说拿到蓝色框的宽高，再根据指定的宽度等比缩放。

示例地址：https://www.iconfont.cn/illustrations/detail?spm=a313x.7781069.1998910419.d9df05512&cid=31456 SVG: https://iconfont.alicdn.com/s/e3430542-d8ce-4a0b-aa2b-91c08ec81b9e_origin.svg

通过升级 resvg 0.15.0 性能上有很大的提升，这个 PR 通过优化编译参数，进一步提升性能，但牺牲了一些编译时间和增加 wasm 文件体积。

Fixes #12

wasm-pack build --release --target nodejs --out-name index --out-dir pkg

在生成图片尺寸为 900px .render(900) 时的测试结果如下：

测试 SVG: https://iconfont.alicdn.com/t/fde3869d-4282-4067-9bc8-25328c558f18_origin.svg

优化方式 | wasm 文件体积 | 生成 PNG 耗时 | 编译时间 -- | -- | -- | -- opt-level = "s", codegen-units = 16 | 1,671,289 字节 | 3391 ms | 11.86s opt-level = 3,codegen-units = 16 | 1,979,951 字节 | 3410 ms | 49.55s opt-level = "s", codegen-units = 1 | 1,636,412 字节 | 2613 ms | 28.10s opt-level = 3, codegen-units = 1 | 1,956,108 字节 | 2272 ms | 16.81s

这个 PR 选择了第四种方式。

插画库：https://www.iconfont.cn/illustrations/detail?cid=26447 SVG 文件：https://iconfont.alicdn.com/s/3dce29fe-78a1-4bed-b788-04805ceda6cf_origin.svg

阴影底部被裁剪（右）

input:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <rect fill="yellow" x="40" y="10" width="20" height="20"/>
  <rect fill="red" x="40" y="40" width="20" height="20" />
  <rect fill="blue" x="40" y="70" width="20" height="20" />
</svg>

output:

<svg width="100" height="100" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
    <defs/>
    <path fill="rgba(255,255,0,255)" stroke="none" d="M 40 10 L 60 10 L 60 30 L 40 30 Z"/>
    <path fill="rgba(255,0,0,255)" stroke="none" d="M 40 40 L 60 40 L 60 60 L 40 60 Z"/>
    <path fill="rgba(0,0,255,255)" stroke="none" d="M 40 70 L 60 70 L 60 90 L 40 90 Z"/>
</svg>

I also hope that the extra stroke="none" can be removed.

We need to remove the transform from the g element and apply it to the child elements.

test case

input:

<svg width="339px" height="237px" viewBox="0 0 339 237" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <g stroke="none" stroke-width="0" fill="none" fill-rule="evenodd">
        <g transform="translate(8.000000, 8.000000)">
            <rect stroke="#979797" stroke-width="15.21" fill="#F7B9B9" x="0" y="0" width="151" height="93"></rect>
            <ellipse stroke-opacity="0.546274038" stroke="#4D5490" stroke-width="10" fill="#94CFFA" cx="257" cy="49.5" rx="68" ry="49.5"></ellipse>
            <rect stroke="#141414" stroke-width="10" fill="#ddd" opacity="0.696607013" x="49" y="133" width="150" height="90" rx="8"></rect>
            <polygon stroke="#979797" stroke-width="5"  fill="#DDB9FE" points="277 202 248.786308 216.832816 254.174644 185.416408 231.349287 163.167184 262.893154 158.583592 277 130 291.106846 158.583592 322.650713 163.167184 299.825356 185.416408 305.213692 216.832816"></polygon>
        </g>
    </g>
</svg>

output:

<svg width="338" height="236" viewBox="0 0 338 236" xmlns="http://www.w3.org/2000/svg">
    <defs/>
    <path fill="rgba(247,185,185,255)" fill-rule="evenodd" stroke="rgba(151,151,151,255)" stroke-width="15.21" d="M 8 8 L 159 8 L 159 101 L 8 101 Z"/>
    <path fill="rgba(148,207,250,255)" fill-rule="evenodd" stroke="rgba(77,84,144,255)" stroke-opacity="0.546274038" stroke-width="10" d="M 333 57.5 C 333 84.83809511662 302.55536298849 107 265 107 C 227.44463701151 107 197 84.83809511662 197 57.5 C 197 30.16190488338 227.44463701151 8 265 8 C 302.55536298849 8 333 30.16190488338 333 57.5 Z"/>
    <g opacity="0.696607013" transform="matrix(1 0 0 1 8 8)">
        <path fill="rgba(221,221,221,255)" fill-rule="evenodd" stroke="rgba(20,20,20,255)" stroke-width="10" d="M 57 133 L 191 133 C 195.41827799865 133 199 136.58172200135 199 141 L 199 215 C 199 219.41827799865 195.41827799865 223 191 223 L 57 223 C 52.58172200135 223 49 219.41827799865 49 215 L 49 141 C 49 136.58172200135 52.58172200135 133 57 133 Z"/>
    </g>
    <path fill="rgba(221,185,254,255)" fill-rule="evenodd" stroke="rgba(151,151,151,255)" stroke-width="5" d="M 285 210 L 256.786308 224.832816 L 262.174644 193.416408 L 239.349287 171.167184 L 270.893154 166.583592 L 285 138 L 299.106846 166.583592 L 330.650713 171.167184 L 307.825356 193.416408 L 313.213692 224.832816 Z"/>
</svg>

<svg id='svg' xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"
     width="256" height="256"
     viewBox="0 0 24 24">
  <!-- gradientUnits defaults to objectBoundingBox -->
  <radialGradient id="radgrad" gradientTransform="rotate(-60 0.5, 0.5) translate(0, 0.2)">
    <stop offset="5%"  stop-color="red" />
    <stop offset="50%" stop-color="gold" />
    <stop offset="95%"  stop-color="red" />
  </radialGradient>
  <circle id="circ"
          cx="5" cy="12"
          r="5"
          fill="url(#radgrad)" />
  <g transform="rotate(120 15,12)">
    <use xlink:href="#circ" x="10" />
  </g>
</svg>

before

after to_string() or render()

Test case

<svg viewBox="0 0 30 10" xmlns="http://www.w3.org/2000/svg">
    <line x1="0" y1="9" x2="30" y2="9" stroke="black" stroke-dasharray="4 1 2 3" />
</svg>

<svg viewBox="0 0 30 10" xmlns="http://www.w3.org/2000/svg">
    <line x1="1" y1="1" x2="5" y2="1" stroke="black" stroke-linecap="butt" />
</svg>

此外还需要判断一下 opacity 和 stroke-opacity = 0 时，无需执行 OutlineStrokeToFill