void main() {
  vec2 uv = gl_FragCoord.xy / resolution;
  vec4 posData = texture2D(texturePosition, uv);
  vec4 velData = texture2D(textureVelocity, uv);

  vec2 pos = posData.xy + velData.xy;

  // Clamp to bounds
  pos = clamp(pos, vec2(-1.0), vec2(1.0));

  gl_FragColor = vec4(pos, posData.zw);
}