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precision highp float;
varying vec3 vWorldPos;
varying vec3 vNormal;
uniform vec3 cameraPos;
uniform vec3 sunDir; // normalized direction from the water toward the sun
uniform vec3 sunColor;
uniform float time;
float hash(vec2 p) {
p = fract(p * vec2(123.34, 456.21));
p += dot(p, p + 45.32);
return fract(p.x * p.y);
}
float valueNoise(vec2 p) {
vec2 i = floor(p);
vec2 f = fract(p);
float a = hash(i);
float b = hash(i + vec2(1.0, 0.0));
float c = hash(i + vec2(0.0, 1.0));
float d = hash(i + vec2(1.0, 1.0));
vec2 u = f * f * (3.0 - 2.0 * f);
return mix(mix(a, b, u.x), mix(c, d, u.x), u.y);
}
void main() {
vec3 N = normalize(vNormal);
vec3 V = normalize(cameraPos - vWorldPos);
// Fresnel (Schlick).
float f0 = 0.02;
float fres = f0 + (1.0 - f0) * pow(1.0 - max(dot(N, V), 0.0), 5.0);
// Refraction: depth-tinted water body, wobbled by the surface normal.
float depth01 = clamp((vWorldPos.z + 350.0) / 400.0, 0.0, 1.0);
float wob = (N.x + N.z) * 0.5;
vec3 shallow = vec3(0.10, 0.55, 0.60);
vec3 deep = vec3(0.02, 0.14, 0.28);
vec3 refractCol = mix(shallow, deep, clamp(depth01 + wob * 0.15, 0.0, 1.0));
// Reflection: sky gradient + reflected sun glow + broken-up specular glitter.
vec3 R = reflect(-V, N);
vec3 skyHorizon = vec3(0.80, 0.88, 0.98);
vec3 skyTop = vec3(0.30, 0.55, 0.95);
float skyT = clamp(R.y * 2.0, 0.0, 1.0);
vec3 reflectCol = mix(skyHorizon, skyTop, skyT);
float sunAmt = max(dot(R, sunDir), 0.0);
reflectCol += sunColor * pow(sunAmt, 8.0) * 0.6;
float sparkle = valueNoise(vWorldPos.xz * 0.5 + vec2(time * 1.3, time * 0.7));
float spec = pow(sunAmt, 200.0) * smoothstep(0.55, 0.9, sparkle);
reflectCol += sunColor * spec * 4.0;
vec3 color = mix(refractCol, reflectCol, fres);
// Horizon haze: hide the far straight edge of the plane by fading to sky.
float horizonFade = clamp((vWorldPos.z + 350.0) / 90.0, 0.0, 1.0);
color = mix(skyHorizon, color, horizonFade);
gl_FragColor = vec4(color, 1.0); // opaque -> occludes the sun below the waterline
}
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