Is it possible to use one SVG shape as the fill of another shape?
You want to use an SVG Pattern. See this example:
<svg viewBox="0 0 800 400" xmlns="http://www.w3.org/2000/svg">
<defs>
<pattern id="TrianglePattern" patternUnits="userSpaceOnUse"
x="0" y="0" width="100" height="100"
viewBox="0 0 10 10" >
<path d="M0,0 L7,0 L3.5,7 z" fill="red" stroke="blue" />
</pattern>
</defs>
<!-- The ellipse is filled using a triangle pattern paint server
and stroked with black -->
<ellipse fill="url(#TrianglePattern)" stroke="black" stroke-width="5"
cx="400" cy="200" rx="350" ry="150" />
</svg>
Note that:
The viewBox
of the <pattern>
will clip what is drawn. (As seen in the example, the top stroke and top-left corner each triangle is slightly hidden.)
When the viewBox
is a different size from the width
and height
you are effectively scaling the size of the graphic(s) in your pattern. (The example scales the 7-unit-wide triangle in the pattern up by a factor of 10, such that only 7 of them—plus padding—are visible across the width of a 700-unit-wide ellipse.)