uniform float uTime;
#pragma glslify: barrelPincushion = require(glsl-barrel-pincushion)
#pragma glslify: rectangle = require(glsl-2d-primitives/rectangle)

attribute vec2 vUv;

void main() {
    vec2 st = barrelPincushion(vUv, sin(uTime));
    float shape = rectangle(st, vec2(0.5));
    gl_FragColor = vec4(color, shape);
}