WebGL fragment shader animation

Above you should see a pulsating colored square. It’s implemented as a WebGL fragment shader. The pulses are a pure function of time. The shader has one uniform parameter, millisecs:

uniform mediump float millisecs;
void main(void) {
  mediump float osc = (sin(millisecs/1000.0) + 1.0) / 2.0;
  gl_FragColor = vec4(osc, osc, osc, 1.0);

The uniform is updated every frame with the new time, then we redraw. So the loop body is only two lines:

const start = new Date().getTime();
window.setInterval(function() {
  gl.uniform1f(millisecsPtr, (new Date().getTime())-start);
  gl.drawArrays(gl.TRIANGLE_FAN, 0, 4);  // draw over the entire viewport
}, 50);

This may not look very exciting, but it’s the core of lots of shader animations. For example, this shader animation renders the current time as a clock.

More by Jim

Tagged . All content copyright James Fisher 2017. This post is not associated with my employer. Found an error? Edit this page.