我正在努力研究SVG元素的内在大小 .
从SVG规范，第8.12. Intrinsic sizing properties of SVG content章，我们知道：
要在使用CSS格式化的主机文档中包含SVG，必须计算具体的对象大小 . 必须使用默认大小调整算法计算具体对象大小
作为默认大小调整算法的输入，我们在同一节中读到：
必须根据'svg'元素的宽度和高度大小调整属性的使用值确定指定的大小 .
然后：
内在尺寸也必须根据宽度和高度尺寸属性确定 . 如果未指定宽度或高度，则使用的值为初始值“auto” . 'auto'和百分比长度不得用于确定固有宽度或固有高度 .
因此，如果我们没有在最外面的svg元素上设置 width 和 height ，我们将内部维度（宽度/高度）设置为 auto （这是模糊的建议） . Default Sizing Algorithm的相关部分：
如果指定的大小没有约束（没有宽度/高度）：如果对象具有固有高度或宽度，则其大小将被解析，就好像其内在大小被指定为指定大小一样 . 否则，将其大小解析为对默认对象大小的包含约束
最后，来自8.3. The initial viewport：
初始视口的宽度，必须是最外层svg元素上宽度表示属性的值...
尽管上面的第一个粗体警告，最外层的svg元素上的 not 和 width 和 height 表示属性是正常的 . 像Adobe Illustrator这样的程序通常会省略这些属性，而只是定义 viewBox .
Thus my questions:
在规范中我可以找到svg元素的使用宽度和高度，如果没有设置 width 和 height 属性？
并且，沿着相同的路线，在同一场景中（只给出一个svg元素），视口尺寸是多少？
作为旁注，来自css-sizing-3 4. Intrinsic Size Determination：
对于具有固有纵横比但没有固有尺寸的框：如果内联轴中的可用空间是确定的，请使用该尺寸的拉伸拟合作为内联尺寸，并使用纵横比计算块尺寸 .
Some code
演示我无法理解的行为（即如何在两个flexbox案例中计算维度） .
注意：当列为列时，flex项的宽度为零 . （这与SVG有关，而不是与flexbox有关） .
.c1,
.c2 {
display: flex;
height: 500px;
align-items: flex-start;
}
.c1 {
flex-flow: row nowrap;
border: 1px solid green;
}
.c1 .i1 {
flex: 0 1 100px;
border: 1px solid blue;
}
.c2 {
flex-flow: column nowrap;
border: 1px solid green;
}
.c2 .i2 {
flex: 0 1 100px;
border: 1px solid red;
}
<div class="c1">
<div class="i1">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 300 300">
<defs>
<g id="SVG" fill="#fff" transform="scale(2) translate(20,79)">
<path id="S" d="M 5.482,31.319 C2.163,28.001 0.109,23.419 0.109,18.358 C0.109,8.232 8.322,0.024 18.443,0.024 C28.569,0.024 36.782,8.232 36.782,18.358 L26.042,18.358 C26.042,14.164 22.638,10.765 18.443,10.765 C14.249,10.765 10.850,14.164 10.850,18.358 C10.850,20.453 11.701,22.351 13.070,23.721 L13.075,23.721 C14.450,25.101 15.595,25.500 18.443,25.952 L18.443,25.952 C23.509,26.479 28.091,28.006 31.409,31.324 L31.409,31.324 C34.728,34.643 36.782,39.225 36.782,44.286 C36.782,54.412 28.569,62.625 18.443,62.625 C8.322,62.625 0.109,54.412 0.109,44.286 L10.850,44.286 C10.850,48.480 14.249,51.884 18.443,51.884 C22.638,51.884 26.042,48.480 26.042,44.286 C26.042,42.191 25.191,40.298 23.821,38.923 L23.816,38.923 C22.441,37.548 20.468,37.074 18.443,36.697 L18.443,36.692 C13.533,35.939 8.800,34.638 5.482,31.319 L5.482,31.319 L5.482,31.319 Z"/>
<path id="V" d="M 73.452,0.024 L60.482,62.625 L49.742,62.625 L36.782,0.024 L47.522,0.024 L55.122,36.687 L62.712,0.024 L73.452,0.024 Z"/>
<path id="G" d="M 91.792,25.952 L110.126,25.952 L110.126,44.286 L110.131,44.286 C110.131,54.413 101.918,62.626 91.792,62.626 C81.665,62.626 73.458,54.413 73.458,44.286 L73.458,44.286 L73.458,18.359 L73.453,18.359 C73.453,8.233 81.665,0.025 91.792,0.025 C101.913,0.025 110.126,8.233 110.126,18.359 L99.385,18.359 C99.385,14.169 95.981,10.765 91.792,10.765 C87.597,10.765 84.198,14.169 84.198,18.359 L84.198,44.286 L84.198,44.286 C84.198,48.481 87.597,51.880 91.792,51.880 C95.981,51.880 99.380,48.481 99.385,44.291 L99.385,44.286 L99.385,36.698 L91.792,36.698 L91.792,25.952 L91.792,25.952 Z"/>
</g>
</defs>
<path id="base" fill="#000" d="M8.5,150 H291.5 V250 C291.5,273.5 273.5,291.5 250,291.5 H50 C26.5,291.5 8.5,273.5 8.5,250 Z"/>
<g stroke-width="38" stroke="#000">
<g id="svgstar" transform="translate(150, 150)">
<path id="svgbar" fill="#ffb13b" d="M-84.1487,-15.8513 a22.4171,22.4171 0 1 0 0,31.7026 h168.2974 a22.4171,22.4171 0 1 0 0,-31.7026 Z"/>
<use xlink:href="#svgbar" transform="rotate(45)"/>
<use xlink:href="#svgbar" transform="rotate(90)"/>
<use xlink:href="#svgbar" transform="rotate(135)"/>
</g>
</g>
<use xlink:href="#svgstar"/>
<use xlink:href="#base" opacity="0.85"/>
<use xlink:href="#SVG"/>
</svg>
</div>
</div>
<div class="c2">
<div class="i2">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 300 300">
<defs>
<g id="SVG" fill="#fff" transform="scale(2) translate(20,79)">
<path id="S" d="M 5.482,31.319 C2.163,28.001 0.109,23.419 0.109,18.358 C0.109,8.232 8.322,0.024 18.443,0.024 C28.569,0.024 36.782,8.232 36.782,18.358 L26.042,18.358 C26.042,14.164 22.638,10.765 18.443,10.765 C14.249,10.765 10.850,14.164 10.850,18.358 C10.850,20.453 11.701,22.351 13.070,23.721 L13.075,23.721 C14.450,25.101 15.595,25.500 18.443,25.952 L18.443,25.952 C23.509,26.479 28.091,28.006 31.409,31.324 L31.409,31.324 C34.728,34.643 36.782,39.225 36.782,44.286 C36.782,54.412 28.569,62.625 18.443,62.625 C8.322,62.625 0.109,54.412 0.109,44.286 L10.850,44.286 C10.850,48.480 14.249,51.884 18.443,51.884 C22.638,51.884 26.042,48.480 26.042,44.286 C26.042,42.191 25.191,40.298 23.821,38.923 L23.816,38.923 C22.441,37.548 20.468,37.074 18.443,36.697 L18.443,36.692 C13.533,35.939 8.800,34.638 5.482,31.319 L5.482,31.319 L5.482,31.319 Z"/>
<path id="V" d="M 73.452,0.024 L60.482,62.625 L49.742,62.625 L36.782,0.024 L47.522,0.024 L55.122,36.687 L62.712,0.024 L73.452,0.024 Z"/>
<path id="G" d="M 91.792,25.952 L110.126,25.952 L110.126,44.286 L110.131,44.286 C110.131,54.413 101.918,62.626 91.792,62.626 C81.665,62.626 73.458,54.413 73.458,44.286 L73.458,44.286 L73.458,18.359 L73.453,18.359 C73.453,8.233 81.665,0.025 91.792,0.025 C101.913,0.025 110.126,8.233 110.126,18.359 L99.385,18.359 C99.385,14.169 95.981,10.765 91.792,10.765 C87.597,10.765 84.198,14.169 84.198,18.359 L84.198,44.286 L84.198,44.286 C84.198,48.481 87.597,51.880 91.792,51.880 C95.981,51.880 99.380,48.481 99.385,44.291 L99.385,44.286 L99.385,36.698 L91.792,36.698 L91.792,25.952 L91.792,25.952 Z"/>
</g>
</defs>
<path id="base" fill="#000" d="M8.5,150 H291.5 V250 C291.5,273.5 273.5,291.5 250,291.5 H50 C26.5,291.5 8.5,273.5 8.5,250 Z"/>
<g stroke-width="38" stroke="#000">
<g id="svgstar" transform="translate(150, 150)">
<path id="svgbar" fill="#ffb13b" d="M-84.1487,-15.8513 a22.4171,22.4171 0 1 0 0,31.7026 h168.2974 a22.4171,22.4171 0 1 0 0,-31.7026 Z"/>
<use xlink:href="#svgbar" transform="rotate(45)"/>
<use xlink:href="#svgbar" transform="rotate(90)"/>
<use xlink:href="#svgbar" transform="rotate(135)"/>
</g>
</g>
<use xlink:href="#svgstar"/>
<use xlink:href="#base" opacity="0.85"/>
<use xlink:href="#SVG"/>
</svg>
</div>
</div>
2 回答
"The ‘viewBox’ attribute, in conjunction with the ‘preserveAspectRatio’ attribute, provides the capability to stretch an SVG viewport to fit a particular container element." .
.i2元素的宽度约为100px . 内部的svg可以调整以适应可用的宽度 ..i1元素的宽度是可用空间的100％ . svg内部缩放以适合.i1的可用宽度 ..i1和.i2元素的宽度由flexbox布局决定 . 如果删除.i1和.i2元素中的svg：.i2将崩溃：默认情况下，空元素的高度为0.它的宽度为100px（由弹性基础确定）.i1不会崩溃，因为's height is determined by the flex basis (100px) while it'的宽度默认为100％ .SVG元素被视为替换元素，并遵守300px x 150px的未大小替换元素的规则 .
您可以在CSS3规范中找到相关的规范语言：
https://www.w3.org/TR/css-sizing-3/