precision highp float;

        varying vec4 vertexPosition;

        void main(void) {

          float radiusSquared = vertexPosition.x * vertexPosition.x + vertexPosition.y * vertexPosition.y;

          float ss = sin(8000.0 * (1.0 - radiusSquared));

          gl_FragColor = vec4(0.0, ss, 0.5, 1.0);

        }