fill-rule

The fill-rule CSS property defines the rule used to determine which parts of the SVG shape's canvas are included inside a shape to be filled. If present, it overrides the element's fill-rule attribute.

The fill-rule clarifies which areas of a shape should be considered "inside" the shape. It provides two values you can set to tell the browser how the inside of a shape should be determined. For shapes that don't have intersecting paths, like a circle, the bounds of what is inside a shape to be filled are intuitively clear. With complex shapes that include intersecting paths (such as a Venn diagram) or paths enclosing other paths (such as a donut), the interpretation of which sections of the shape are "inside" the shape and should be filled by the fill property, may not be obvious.

Note: The fill-rule property only applies to <path>, <polygon>, <polyline>, <text>, <textPath>, and <tspan> elements nested in an <svg>. It doesn't apply to other SVG, HTML, or pseudo-elements.

Syntax

css

/* keywords */
fill-rule: evenodd;
fill-rule: nonzero;

/* Global values */
fill-rule: inherit;
fill-rule: initial;
fill-rule: revert;
fill-rule: revert-layer;
fill-rule: unset;

Values

nonzero: For every point in the shape, a ray is drawn in a random direction to beyond the shape's outer edges. Each ray is examined to determine the places where the ray crosses the shape. Starting with a count of zero, add one each time a path segment crosses the ray from left to right and subtract one each time a path segment crosses the ray from right to left. After counting the crossings, if the result is zero then the point is outside the path. Otherwise, it is inside.
evenodd: For every point in the fill rule's box, a ray is drawn in a random direction. The number of path segments from the given shape that the ray crosses are counted. If this number is odd, the point is inside; if even, the point is outside. Zero is taken to be even.

Formal definition

Value not found in DB!

Formal syntax

fill-rule = 
nonzero  |
evenodd

Examples

Defining the fill rules for SVG elements

This example demonstrates how a fill-rule is declared, the effect of the property, and how the CSS fill-rule property takes precedence over the fill-rule attribute.

HTML

We define an SVG with two complex shapes defined using the SVG <polygon> and <path> elements. The polygon has the SVG fill-rule attribute set to evenodd and the star-shaped path is set to nonzero, which is the default. To make the lines visible, we set the outline to red using the SVG stroke attribute (we could have alternatively used the stroke property).

<p>Original SVG</p>

html

<svg viewBox="0 0 220 120" xmlns="http://www.w3.org/2000/svg">
  <polygon
    points="180,10 150,100 220,40 140,40 210,100"
    stroke="red"
    fill-rule="evenodd" />
  <path
    d="M 10,5 l 90,0 -80,80 0,-60 80,80 -90,0 z"
    stroke="red"
    fill-rule="nonzero" />
</svg>

<p><code>fill-rule: nonzero;</code></p>
<svg viewBox="0 0 220 120" xmlns="http://www.w3.org/2000/svg">
  <polygon
    points="180,10 150,100 220,40 140,40 210,100"
    stroke="red"
    fill-rule="evenodd" />
  <path
    d="M 10,5 l 90,0 -80,80 0,-60 80,80 -90,0 z"
    stroke="red"
    fill-rule="nonzero" />
</svg>
<p><code>fill-rule: evenodd;</code></p>
<svg viewBox="0 0 220 120" xmlns="http://www.w3.org/2000/svg">
  <polygon
    points="180,10 150,100 220,40 140,40 210,100"
    stroke="red"
    fill-rule="evenodd" />
  <path
    d="M 10,5 l 90,0 -80,80 0,-60 80,80 -90,0 z"
    stroke="red"
    fill-rule="nonzero" />
</svg>

The above SVG is repeated three times; we've only shown one copy for the sake of brevity.

CSS

The shapes nested in the first SVG have no CSS applied. We set the shapes inside the second SVG to use the nonzero value. The third SVG has all its nested shapes set to evenodd.

svg {
  border: 1px solid;
  height: calc(33vh - 2.5em);
  margin-bottom: 10px;
}
p {
  margin: 0;
}

css

svg:nth-of-type(2) > * {
  fill-rule: nonzero;
}
svg:nth-of-type(3) > * {
  fill-rule: evenodd;
}

Results

With the nonzero value for fill-rule, the "inside" of the shape is the entire shape. The evenodd value defines some space as empty. The first image renders the fill-rule included as an attribute. Declaring the fill-rule in the CSS overrides the attribute values in the second and third images.

Specifications

Specification
CSS Fill and Stroke Module Level 3 # fill-rule

Browser compatibility

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