ShaderToyにいい実装があったので，自分なりにパラメータ調整したやつ。
// Based on: https://www.shadertoy.com/view/3d3yRj
// See also: KdotJPG's https://www.shadertoy.com/view/wlc3zr
float water_caustics(vec3 pos, float thickness) {
vec4 n = snoise( pos );
pos -= thickness*n.xyz;
n = snoise( pos );
pos -= thickness*n.xyz;
n = snoise( pos );
pos -= thickness*n.xyz;
n = snoise( pos );
return n.w;
}
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
vec2 p = (-iResolution.xy + 2.0*fragCoord) / iResolution.y;
// camera matrix
vec3 ww = normalize(-vec3(0., 1., 0.8));
vec3 uu = normalize(cross(ww, vec3(0., 1., 0.)));
vec3 vv = normalize(cross(uu,ww));
vec3 rd = p.x*uu + p.y*vv + 1.5*ww; // view ray
vec3 pos = -ww + rd*(ww.y/rd.y); // raytrace plane
pos.y = iTime*0.25; // animate noise slice
pos *= 3.; // tiling frequency
float w = mix(water_caustics(pos, 0.085), water_caustics(pos + 1.0, 0.085), 0.5);
// noise [-1..+1] -> color
float intensity = exp(w*2.5 - 1.);
fragColor = vec4(vec3(intensity), 1.);
}
ちなみに元にしたコードは，https://www.shadertoy.com/view/ssfBDfにあります。
