Gradients

Basic application of SVG Linear and Radial Gradients to SVG Elements

For reference take a look at the MDN SVG Gradient Docs

SVG has provides us with two different gradient elements, namely linearGradient and radialGradient which can be applied as fills or strokes to SVG elements

Gradients work by defining them inside of a defs element so that they can be reused in multiple parts of an SVG and they must have an id attribute so they can be referenced by other elements

Defining Gradients

The stop Element

When defining any type of gradient it's necessary to define a stops. A stop defines a color and it's position and is always a child of a linearGradient or radialGradient element

A stop has the following properties:

1. offset - where the stop should be placed along the gradient. Can either be a number of a percentage, offset="0.5" or offset="50%" for example. Default is 0
2. stop-color - The color associated with the stop. Default is black
3. stop-opacity - The opacity associated with the stop Default is 1

A gradient does not need to define all of the above properties but you likely will want to in order to effectively define a gradient

Some examples of a stop using the above definitions can be seen below:

<stop stop-color="blue"/>
<stop stop-color="#E2E2E2" offset="0.5" />
<stop stop-color="#D5E73F" stop-opacity="0.7" offset="80%" />

The linearGradient Element

Linear gradients are gradients that change along a straight line (the gradient vector).

Creating a linearGradient in the defs section of an SVG file looks like so:

<defs>
  <linearGradient id="linear">
    <stop stop-color="blue"/>
    <stop stop-color="#E2E2E2" offset="0.5" />
    <stop stop-color="#D5E73F" stop-opacity="0.7" offset="80%" />
  </linearGradient>
</defs>

Additionally we can control the position/direction of the gradient vector by changing it's start and end points using the x1, x2, y1, and y2 values.

So a horizontal gradient (the default) would look something like this:

<linearGradient id="linear" x1="0" y1="0" x2="1" y2="0">

And a vertical one like so:

<linearGradient id="linear" x1="0" y1="0" x2="0" y2="1">

The radialGradient Element

Radial Gradients are gradients that change along a a radius from a defined focal point

Creating a radialGradient in the defs section of an SVG file looks like so:

<defs>
  <radialGradient id="radial">
    <stop stop-color="blue"/>
    <stop stop-color="#E2E2E2" offset="0.5" />
    <stop stop-color="#D5E73F" stop-opacity="0.7" offset="80%" />
  </linearGradient>
</defs>

For a radialGradient we can also control the radius, center point positions, and focal point radius, and focal point positions using r, cx, cy, fr, fx, and fy respectively

To define a gradient with a small center radius, we can do something like this:

<radialGradient id="radial" r="0.5" />

Or for a gradient which is off-center we can do this:

<radialGradient id="radial" cx="0.2" cy="0.2" />

And likewise for changing the focal point:

<radialGradient id="radial" fx="0.2" fy="0.2" />

Or using fr instead:

<radialGradient id="radial" fr="0.2" />

Using Gradients

Using SVG Gradients can be done by referencing the gradient from the fill or stroke property of an SVG element

For example, I can use the linearGradient defined above for a circle's fill with:

<circle 
  cx="50" 
  cy="50"
  r="40" 
  fill="url(#linear)" 
/>

Or for the stroke on a path with:

<path 
  d="M 0 100 L 10 40 L 100 50" 
  stroke-width="1" 
  fill="transparent" 
  stroke="url(#linear)" 
/>

A more complete example using the linearGradient and radialGradient can be seen below:

<svg viewBox="0 0 100 100"  xmlns="http://www.w3.org/2000/svg"
     xmlns:xlink="http://www.w3.org/1999/xlink">
  <defs>
    <linearGradient id="linear" x1="0" y1="0" x2="0" y2="1">
      <stop stop-color="blue"/>
      <stop stop-color="#E2E2E2" offset="0.5" />
      <stop stop-color="#D5E73F" stop-opacity="0.7" offset="80%" />
    </linearGradient>
   <radialGradient id="radial" fr="0" r="0.7" cx="0.3" cy="0.3">
      <stop stop-color="blue"/>
      <stop stop-color="#E2E2E2" offset="0.5" />
      <stop stop-color="#D5E73F" stop-opacity="0.7" offset="80%" />
    </linearGradient>
  </defs>

  <circle cx="50" cy="50" r="40" fill="url(#radial)" />
  <path d="M 0 100 L 10 40 L 100 50" stroke-width="1" stroke="url(#linear)" fill="transparent" />
</svg>

And the result: