FakeCaustics.osl

// Found this on GLSL sandbox. I really liked it, changed a few things and made it tileable.
// by David Hoskins.
// Water turbulence effect by joltz0r 2013-07-04, improved 2013-07-07
// Updated 1/4/2020 by Saul Espinosa for Redshift 3D
// This file is licensed under Apache 2.0 license


// Redefine below to see the tiling...
//#define SHOW_TILING

#define TAU 6.28318530718


shader FakeCaustics
[[  string help = "generates a psuedo caustic like noise pattern",
    string label = "Fake Caustics" ]]
( 

	point Po = P,
	float Time = 0
	[[
	float min = 0, float max = 100
	]],
	int iterations = 5
	[[
	int min = 0, int max = 20
	]],
	output color Out = 0,
  
    ) 
{
	float tt = Time * .5+23.0;
    // uv should be the 0-1 uv of texture...
	vector uv = Po;
    
	vector p = mod(uv*TAU*2.0, TAU)-250.0;

    // vector p = mod(uv*TAU, TAU)-250.0;

	vector i = vector(p);
	float c = 1.0;
	float inten = .005;

	for (int n = 0; n < iterations; n++) 
	{
		float t = tt * (1.0 - (3.5 / float(n+1)));
		i = p + vector(cos(t - i[0]) + sin(t + i[1]), sin(t - i[1]) + cos(t + i[0]),0);
		c += 1.0/length(vector(p[0] / (sin(i[0]+t)/inten),p[1] / (cos(i[1]+t)/inten),0));
	}
	c /= float(iterations);
	c = 1.17-pow(c, 1.4);
	vector colour = vector(pow(abs(c), 8.0));
    colour = clamp(colour + vector(0.0, 0.35, 0.5), 0.0, 1.0);
    
/*
	#ifdef SHOW_TILING
	// Flash tile borders...
	vec2 pixel = 2.0 / iResolution.xy;
	uv *= 2.0;

	float f = floor(mod(iTime*.5, 2.0)); 	// Flash value.
	vec2 first = step(pixel, uv) * f;		   	// Rule out first screen pixels and flash.
	uv  = step(fract(uv), pixel);				// Add one line of pixels per tile.
	colour = mix(colour, vec3(1.0, 1.0, 0.0), (uv.x + uv.y) * first.x * first.y); // Yellow line
	
*/
	Out = vector(colour);
	Out = pow(Out,2.2);
}