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/**
** sipp - SImple Polygon Processor
**
** A general 3d graphic package
**
** Copyright Equivalent Software HB 1992
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 1, or any later version.
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU General Public License for more details.
** You can receive a copy of the GNU General Public License from the
** Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
**/
/**
** phong_shader.c - The traditional Phong shading function.
**/
#include <math.h>
#include <sipp.h>
#include <geometric.h>
#include <shaders.h>
void
phong_shader(pos, normal, texture, view_vec, lights, pd, color, opacity)
Vector *pos;
Vector *normal;
Vector *texture;
Vector *view_vec;
Lightsource *lights;
Phong_desc *pd;
Color *color;
Color *opacity;
{
Vector unit_norm;
Vector light_dir;
Vector specular;
Color diffsum;
Color specsum;
double cos_theta;
double cos_alpha;
double light_fraction;
double spec_factor;
Lightsource *lp;
VecCopy(unit_norm, *normal);
vecnorm(&unit_norm);
diffsum.red = diffsum.grn = diffsum.blu = 0.0;
specsum.red = specsum.grn = specsum.blu = 0.0;
for (lp = lights; lp != (Lightsource *)0; lp = lp->next) {
light_fraction = light_eval(lp, pos, &light_dir);
if (light_fraction > 0.0001) {
cos_theta = VecDot(light_dir, unit_norm);
if (cos_theta > 0) {
diffsum.red += lp->color.red * cos_theta * light_fraction;
diffsum.grn += lp->color.grn * cos_theta * light_fraction;
diffsum.blu += lp->color.blu * cos_theta * light_fraction;
}
cos_theta *= 2.0;
VecComb(specular, -1.0, light_dir, cos_theta, unit_norm);
cos_alpha = VecDot(specular, *view_vec);
if (cos_alpha > 0) {
spec_factor = light_fraction * exp(pd->spec_exp
* log(cos_alpha));
specsum.red += lp->color.red * spec_factor;
specsum.grn += lp->color.grn * spec_factor;
specsum.blu += lp->color.blu * spec_factor;
}
}
}
if (diffsum.red > 1.0) diffsum.red = 1.0;
if (diffsum.grn > 1.0) diffsum.grn = 1.0;
if (diffsum.blu > 1.0) diffsum.blu = 1.0;
if (specsum.red > 1.0) specsum.red = 1.0;
if (specsum.grn > 1.0) specsum.grn = 1.0;
if (specsum.blu > 1.0) specsum.blu = 1.0;
color->red = (pd->color.red * (pd->ambient + pd->diffuse * diffsum.red)
+ pd->specular * specsum.red);
if (color->red > 1.0) color->red = 1.0;
color->grn = (pd->color.grn * (pd->ambient + pd->diffuse * diffsum.grn)
+ pd->specular * specsum.grn);
if (color->grn > 1.0) color->grn = 1.0;
color->blu = (pd->color.blu * (pd->ambient + pd->diffuse * diffsum.blu)
+ pd->specular * specsum.blu);
if (color->blu > 1.0) color->blu = 1.0;
opacity->red = pd->opacity.red;
opacity->grn = pd->opacity.grn;
opacity->blu = pd->opacity.blu;
}
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