precision highp float;
precision highp int;

#include <utils>

in vec3 oldPos;
in vec3 newPos;
in vec3 ray;

out vec4 fragColor;

void main() {
  /* if the triangle gets smaller, it gets brighter, and vice versa */
  float oldArea = length(dFdx(oldPos)) * length(dFdy(oldPos));
  float newArea = length(dFdx(newPos)) * length(dFdy(newPos));
  fragColor = vec4(oldArea / newArea * 0.2, 1.0, 0.0, 0.0);

  vec3 refractedLight = refract(-light, vec3(0.0, 1.0, 0.0), IOR_AIR / IOR_WATER);

  /* shadow for the rim of the pool */
  vec2 t = intersectCube(
    newPos,
    -refractedLight,
    vec3(-poolHalfSize.x, -poolHeight, -poolHalfSize.y),
    vec3(poolHalfSize.x, poolHeight * 2.0, poolHalfSize.y)
  );
  fragColor.r *= 1.0 / (1.0 + exp(-200.0 / (1.0 + 10.0 * (t.y - t.x)) * (newPos.y - refractedLight.y * t.y - poolHeight * 2.0 / 12.0)));
}