getParticleFragmentShader = ({ particleShape, transparency }) => `
// Color from uniforms arg
uniform vec3 color;

// Color calculated from vertex shader, based on particle position
varying vec3 vColor;

void main() {
  ${particleShape === 'circle' ? circleParticleShape : ''}
  gl_FragColor = vec4(vColor, ${transparency});
}
`
Applies a shape to each particle

@param {String} particleShape Either 'circle' or 'square'
@param {Number} transparency The alpha channel rgba value for particles