/******************************************************************************/
/*                                                                            */
/*    Copyright (c)The 3Delight Team.                                         */
/*    All Rights Reserved.                                                    */
/*                                                                            */
/******************************************************************************/

/*
	A light source for image based lighting. 
	
	PARAMETERS
	light_color
              : a multiplier on the light from the envmap.
	Kenv      : intensity multiplier
	Kocc      : if >0, trace transmission rays to take into account occlusion
	            by other objects
	envmap    : the environment map to use
	envspace  : the coordinate system where to place the environment map
	samples   : number of samples to use to compute lighting. Setting samples
	            to 0 will use the SH-based indirectdiffuse approximation
	            without ray-tracing.
	bias      : ray-tracing bias.
*/
light lm_envlight2(
	color light_color = 1;
	float Kenv = 1.0;
 	float Kocc = 0.0;
	string envmap = "", envspace = "world";
	float samples = 64; 
	float maxdist = 1e10;
	float bias = -1;
	string __category = "env";
	float __nonspecular = 1;
)
{
	uniform string raytype="";
	rayinfo( "type", raytype );

	uniform string gather_cat = concat("environment:", envmap);
	vector envdir = 0;
	color envcolor = 0;
	float solidangle = 0;

	if( raytype == "light" )
	{
		/* This light is called to cast some photons. Use gather() to give us
		   the most intersting directions and use a solar() construct to cast
		   a photon coming from that direction. (The photon casting process
		   is dealt with automagically inside 3Delight) */

		gather(
			gather_cat, 0, 0, 0, samples,
			"environment:color", envcolor,
			"environment:direction", envdir,
			"environment:solidangle", solidangle )
		{
			envdir = vtransform( envspace, "current", envdir );

			/* Convert from solid angle to angle */
			solar( -envdir, acos( 1-solidangle/(2*PI) ))
			{
				Cl = envcolor * light_color / (4*PI);
			}
		}
	}
	else
	{
		normal shading_normal = normalize(Ns);

		if( samples == 0 )
		{
			/* Use the SH-based approximation. */

			normal tN = ntransform( envspace, shading_normal );
			illuminate( Ps + shading_normal ) /* shade all surface points */
			{
				Cl = Kenv * light_color * indirectdiffuse( envmap, tN ) / (4*PI);
			}
		}
		else
		{
			uniform float t1 = 0.025 * sqrt(samples);
			uniform float t2 = 0.05 * sqrt(samples);

			illuminate( Ps + shading_normal ) /* shade all surface points */
			{
				Cl = 0;

				if( Kenv > 0 )
				{
					vector raydir = 0;

					gather(
						gather_cat, 0, 0, 0, samples,
						"environment:color", envcolor,
						"ray:direction", raydir,
						"environment:direction", envdir,
						"environment:solidangle", solidangle )
					{
						raydir = vtransform( envspace, "current", raydir );
						envdir = vtransform( envspace, "current", envdir );

						float atten = max( shading_normal . normalize(envdir), 0 );

						float kocc = 1 - smoothstep( t1, t2, solidangle );
						kocc *= Kocc;

						uniform float diffusedepth = 0;
						attribute( "diffusedepth", diffusedepth );

						color trs = 1;
						if( kocc > 0 && atten > 0 && diffusedepth==0 )
						{
							trs = transmission(
									Ps, Ps + raydir * maxdist, "bias", bias );
							trs = 1 - kocc * (1 - trs);
						}

						Cl += envcolor * trs * atten * light_color / (4*PI);
					}

					Cl *= Kenv;
				}
			}
		}
	}
}