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POGet bounding box of element accounting for its transform
 

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    <p>Given this SVG:</p> <pre><code>&lt;svg xmlns="http://www.w3.org/2000/svg"&gt; &lt;rect width="50" height="50" transform="translate(75,75) rotate(45) translate(-25,-25)" /&gt; &lt;script&gt; var bb = document.querySelector('rect').getBBox(); console.log([bb.x,bb,y,bb.width,bb.height]); &lt;/script&gt; &lt;/svg&gt;​ </code></pre> <p>The resulting output is <code>[0, 0, 50, 50]</code>.<br> The desired result is <code>[39.645,39.645,70.711,70.711]</code>.</p> <h2>Visual Version: <a href="http://jsfiddle.net/2wpju/7/" rel="noreferrer">http://jsfiddle.net/2wpju/7/</a></h2> <p>What's the simplest, most efficient way to calculate the bounding box of an element with respect to its parent element?</p> <hr> <p>Below is the best answer I've come up with so far, but there are two problems:</p> <ol> <li>It seems like a lot of work for what might be handled better, and</li> <li>As seen in <strong><a href="http://jsfiddle.net/2wpju/4/" rel="noreferrer">this demo</a></strong> it's not necessarily the minimum bounding box (notice the upper circle), since the axis-aligned bounding box of a rotated axis-aligned bounding box always increases the size.</li> </ol> <p>&nbsp;</p> <pre class="lang-js prettyprint-override"><code>// Calculate the bounding box of an element with respect to its parent element function transformedBoundingBox(el){ var bb = el.getBBox(), svg = el.ownerSVGElement, m = el.getTransformToElement(el.parentNode); // Create an array of all four points for the original bounding box var pts = [ svg.createSVGPoint(), svg.createSVGPoint(), svg.createSVGPoint(), svg.createSVGPoint() ]; pts[0].x=bb.x; pts[0].y=bb.y; pts[1].x=bb.x+bb.width; pts[1].y=bb.y; pts[2].x=bb.x+bb.width; pts[2].y=bb.y+bb.height; pts[3].x=bb.x; pts[3].y=bb.y+bb.height; // Transform each into the space of the parent, // and calculate the min/max points from that. var xMin=Infinity,xMax=-Infinity,yMin=Infinity,yMax=-Infinity; pts.forEach(function(pt){ pt = pt.matrixTransform(m); xMin = Math.min(xMin,pt.x); xMax = Math.max(xMax,pt.x); yMin = Math.min(yMin,pt.y); yMax = Math.max(yMax,pt.y); }); // Update the bounding box with the new values bb.x = xMin; bb.width = xMax-xMin; bb.y = yMin; bb.height = yMax-yMin; return bb; } </code></pre>
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    1. COInterestingly, the "too big" example of the rotated circle is same as the result of calling `getBoundingClientRect()` for the element, on all major browsers. Apparently they internally do the same thing (find the local bounding rect and then transform those points into screen space).
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    2. COPrevious comment [does not apply to Firefox](http://stackoverflow.com/questions/10628851/what-should-getboundingclientrect-on-a-transformed-svg-element-return).
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    3. COcool, works as expected
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