Question

I’d like to generate an SVG gradient that varies over time.

In this example code, I’d like to generate an ellipse whose gradient is red with a yellow stripe that travels from west to east over time (creating a shimmer effect):

<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
  <defs>
    <linearGradient id="grad1" x1="0%" y1="0%" x2="100%" y2="0%">
      <stop offset="0%" style="stop-color:rgb(255,0,0);stop-opacity:1" />
      <stop offset="0%" style="stop-color:rgb(255,255,0);stop-opacity:1" >
        <animate 
          attributeName="offset" 
          from="0%"
          to="100%"
          repeatCount="indefinite"/>
      </stop>
      <stop offset="100%" style="stop-color:rgb(255,0,0);stop-opacity:1" />
    </linearGradient>
  </defs>
  <ellipse cx="200" cy="70" rx="85" ry="55" fill="url(#grad1)" />
</svg>

This doesn’t work yet, but I’m not sure whether it’s because I’m doing it wrong, or it’s not an effect I can achieve with SVG gradients.

Answer 1

You just need a time period for the animation. Add dur="5s" for instance as an attribute of the animate element.

<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
  <defs>
    <linearGradient id="grad1" x1="0%" y1="0%" x2="100%" y2="0%">
      <stop offset="0%" style="stop-color:rgb(255,0,0);stop-opacity:1" />
      <stop offset="0%" style="stop-color:rgb(255,255,0);stop-opacity:1" >
        <animate 
          attributeName="offset" 
          from="0%"
          to="100%"
          dur="5s"
          repeatCount="indefinite"/>
      </stop>
      <stop offset="100%" style="stop-color:rgb(255,0,0);stop-opacity:1" />
    </linearGradient>
  </defs>
  <ellipse cx="200" cy="70" rx="85" ry="55" fill="url(#grad1)" />
</svg>