precision mediump float;

varying vec4 clipSpace;

uniform sampler2D reflectionTexture;
uniform sampler2D refractionTexture;
uniform sampler2D dudvMap;

varying vec2 uv;
const float waveStrength = 0.002;

void main() {
  vec2 ndc = (clipSpace.xy / clipSpace.w) / 2.0 + 0.5;
  vec2 refractTexCoords = vec2(ndc.x, ndc.y);
  vec2 reflectTexCoords = vec2(ndc.x, 1.0 - ndc.y);

  vec2 distortion1 = texture2D(dudvMap, uv).xy * 2.0 - 1.0 * waveStrength;
  refractTexCoords += distortion1;
  refractTexCoords = clamp(refractTexCoords, 0.001, 0.999);
  reflectTexCoords += distortion1;
  reflectTexCoords.x = clamp(reflectTexCoords.x, 0.001, 0.999);
  reflectTexCoords.y = clamp(reflectTexCoords.y, -0.999, -0.001);

  vec4 reflectColor = texture2D(reflectionTexture, reflectTexCoords);
  vec4 refractColor = texture2D(refractionTexture, refractTexCoords);

  gl_FragColor = mix(reflectColor, refractColor, 0.5);
}