Fixed stroke width in SVG

I would like to be able to set the stroke-width on an SVG element to be "pixel-aware", that is always be 1px wide regardless of the current scaling transformations applied. I am aware that this may well be impossible, since the whole point of SVG is to be pixel independent.

Context follows:

I have an SVG element with its viewBox and preserveAspectRatio attributes set. It looks something like this

<svg version="1.1" baseProfile="full"
    viewBox="-100 -100 200 200" preserveAspectRatio="xMidYMid meet"
    xmlns="http://www.w3.org/2000/svg" >
</svg>

This means that when I scale that element, the actual shapes inside it scale accordingly (so far so good).

As you can see, I have set up the viewBox so that the origin is in the center. I would like to draw an x- and a y-axis within that element, which I do thus:

<line x1="-1000" x2="1000" y1="0" y2="0" />

Again, this works fine. Ideally, though, this axis would always be only 1px wide. I have no interest in the axes getting fatter when i scale the parent svg element.

So am I screwed?

Solution 1:

You can use the vector-effect property set to non-scaling-stroke, see the docs. Another way is to use transform(ref).

That will work in browsers that support those parts from SVG Tiny 1.2, for example Opera 10. The fallback includes writing a small script to do the same, basically inverting the CTM and applying it on the elements that shouldn't scale.

If you want sharper lines you can also disable antialiasing (shape-rendering=optimizeSpeed or shape-rendering=crispEdges) and/or play with the positioning.

Solution 2:

Here is a more concise answer based on Erik's answer to help you get started quickly.

<div style="background: blue; width: 100%; height: 130px;">
            <svg xml:id="root" viewBox="0 0 100 100" width="100%" height="100%" preserveAspectRatio="none">
                <rect xml:id="r" vector-effect="non-scaling-stroke" x="0" y="0" width="100" height="100" fill="none" stroke="#88CE02"
                      stroke-linecap="square" stroke-width="10" stroke-miterlimit="30"/>
            </svg>
        </div>

Adding the vector-effect="non-scaling-stroke" to the SVG rect makes the border size (or stroke size) fixed.