/******************************************************************************
 * Copyright 1986-2004 by mental images GmbH, Fasanenstr. 81, D-10623 Berlin,
 * Germany. All rights reserved.
 ******************************************************************************
 * Created:	10.02.98
 * Module:	baseshader
 * Purpose:	base shaders for Phenomenon writers
 *
 * Exports:
 *      mib_illum_ward_deriv
 *      mib_illum_ward_deriv_version
 *
 * History:
 *
 * Description:
 *      Perform illumination with the following reflection model:
 *      - Ward anisotropic glossy plus
 *      - Lambert diffuse (cosine) plus
 *      - ambient (constant)
 *
 * The anisotropic Ward reflection model of glossy reflection was
 * developed in "Measuring and modeling anisotropic reflection" by
 * Gregory J. Ward, Proceedings of Siggraph '92, pp. 265--272.
 * The brushing directions (u and v) are taken from the surface derivatives
 *****************************************************************************/

#include <math.h>
#include <assert.h>
#include "shader.h"

#define INTENSITY(c)	((1./3) * ((c).r + (c).g + (c).b))
#define miEPS		0.0001


struct mib_illum_ward_deriv {
	miColor		ambience;	/* ambient color multiplier */
	miColor		ambient;	/* ambient color */
	miColor		diffuse;	/* diffuse color */
	miColor		glossy;		/* glossy color */
	miScalar	shiny_u;	/* shiny coef in u direction (5-100) */
	miScalar	shiny_v;	/* shiny coef in v direction (5-100) */
	int		mode;		/* light mode: 0..2 */
	int		i_light;	/* index of first light */
	int		n_light;	/* number of lights */
	miTag		light[1];	/* list of lights */
};


DLLEXPORT int mib_illum_ward_deriv_version(void) { return(1); }

DLLEXPORT miBoolean mib_illum_ward_deriv(
	miColor		*result,
	miState		*state,
	struct mib_illum_ward_deriv *paras)
{
	miColor		*ambi, *diff, *glos;
	miTag		*light;		/* tag of light instance */
	int		n_l;		/* number of light sources */
	int		i_l;		/* offset of light sources */
	int		m;		/* light mode: 0=all, 1=incl, 2=excl */
	int		n;		/* light counter */
	int		samples;	/* # of samples taken */
	miColor		color;		/* color from light source */
	miColor		sum;		/* summed sample colors */
	miVector	dir;		/* direction towards light */
	miScalar	dot_nl;		/* dot prod of normal and dir */
	miScalar	shiny_u;	/* shiny coef in u direction (5-100) */
	miScalar	shiny_v;	/* shiny coef in v direction (5-100) */
	miScalar	s;		/* amount of specular reflection */

        /* check for illegal calls */
        if (state->type == miRAY_SHADOW || state->type == miRAY_DISPLACE ) {
		return(miFALSE);
	}

        
	ambi    =  mi_eval_color(&paras->ambient);
	diff    =  mi_eval_color(&paras->diffuse);
	glos    =  mi_eval_color(&paras->glossy);
	shiny_u = *mi_eval_scalar(&paras->shiny_u);
	shiny_v = *mi_eval_scalar(&paras->shiny_v);
	m       = *mi_eval_integer(&paras->mode);

	*result    = *mi_eval_color(&paras->ambience);	/* ambient term */
	result->r *= ambi->r;
	result->g *= ambi->g;
	result->b *= ambi->b;

	n_l   = *mi_eval_integer(&paras->n_light);
	i_l   = *mi_eval_integer(&paras->i_light);
	light = mi_eval_tag(paras->light) + i_l;

	if (m == 1)		/* modify light list (inclusive mode) */
		mi_inclusive_lightlist(&n_l, &light, state);
	else if (m == 2)	/* modify light list (exclusive mode) */
		mi_exclusive_lightlist(&n_l, &light, state);

	/* Loop over all light sources */
	for (n=0; n < n_l; n++, light++) {
		sum.r = sum.g = sum.b = 0;
		samples = 0;
		while (mi_sample_light(&color, &dir, &dot_nl, state,
						*light, &samples)) {
			/* Lambert's cosine law */
			sum.r += dot_nl * diff->r * color.r;
			sum.g += dot_nl * diff->g * color.g;
			sum.b += dot_nl * diff->b * color.b;

			/* Ward's glossy reflection */
			if (shiny_u == shiny_v)		/* isotropic refl. */
				s = dot_nl * mi_ward_glossy(&state->dir, &dir,
						&state->normal, shiny_u);

			else {				/* anisotropic refl. */
				miVector	u, v;
				float		d;

				u    = state->derivs[0];
				d    = mi_vector_dot(&u, &state->normal);
				u.x -= d * state->normal.x;
				u.y -= d * state->normal.y;
				u.z -= d * state->normal.z;
				mi_vector_normalize(&u);

				/* Set v to be perpendicular to u */
				/* (in the tangent plane) */
				mi_vector_prod(&v, &state->normal, &u);
				s = dot_nl * mi_ward_anisglossy(&state->dir,
						&dir, &state->normal,
						&u, &v, shiny_u, shiny_v);
			}
			if (s > 0.0) {
				sum.r += s * glos->r * color.r;
				sum.g += s * glos->g * color.g;
				sum.b += s * glos->b * color.b;
			}
		}
		if (samples) {
			result->r += sum.r / samples;
			result->g += sum.g / samples;
			result->b += sum.b / samples;
		}
	}

	/* add contribution from indirect illumination (caustics) */
	mi_compute_irradiance(&color, state);
	result->r += color.r * diff->r;
	result->g += color.g * diff->g;
	result->b += color.b * diff->b;
	result->a  = 1;
	return(miTRUE);
}