point light illumination using Phong model
- by Myx
Hello:
I wish to render a scene that contains one box and a point light source using the Phong illumination scheme. The following are the relevant code snippets for my calculation:
R3Rgb Phong(R3Scene *scene, R3Ray *ray, R3Intersection *intersection)
{
R3Rgb radiance;
if(intersection->hit == 0)
{
radiance = scene->background;
return radiance;
}
...
// obtain ambient term
... // this is zero for my test
// obtain emissive term
... // this is also zero for my test
// for each light in the scene, obtain calculate the diffuse and specular terms
R3Rgb intensity_diffuse(0,0,0,1);
R3Rgb intensity_specular(0,0,0,1);
for(unsigned int i = 0; i < scene->lights.size(); i++)
{
R3Light *light = scene->Light(i);
R3Rgb light_color = LightIntensity(scene->Light(i), intersection->position);
R3Vector light_vector = -LightDirection(scene->Light(i), intersection->position);
// check if the light is "behind" the surface normal
if(normal.Dot(light_vector)<=0)
continue;
// calculate diffuse reflection
if(!Kd.IsBlack())
intensity_diffuse += Kd*normal.Dot(light_vector)*light_color;
if(Ks.IsBlack())
continue;
// calculate specular reflection
... // this I believe to be irrelevant for the particular test I'm doing
}
radiance = intensity_diffuse;
return radiance;
}
R3Rgb LightIntensity(R3Light *light, R3Point position)
{
R3Rgb light_intensity;
double distance;
double denominator;
if(light->type != R3_DIRECTIONAL_LIGHT)
{
distance = (position-light->position).Length();
denominator = light->constant_attenuation +
(light->linear_attenuation*distance) +
(light->quadratic_attenuation*distance*distance);
}
switch(light->type)
{
...
case R3_POINT_LIGHT:
light_intensity = light->color/denominator;
break;
...
}
return light_intensity;
}
R3Vector LightDirection(R3Light *light, R3Point position)
{
R3Vector light_direction;
switch(light->type)
{
...
case R3_POINT_LIGHT:
light_direction = position - light->position;
break;
...
}
light_direction.Normalize();
return light_direction;
}
I believe that the error must be somewhere in either LightDirection(...) or LightIntensity(...) functions because when I run my code using a directional light source, I obtain the desired rendered image (thus this leads me to believe that the Phong illumination equation is correct). Also, in Phong(...), when I computed the intensity_diffuse and while debugging, I divided light_color by 10, I was obtaining a resulting image that looked more like what I need. Am I calculating the light_color correctly?
Thanks.
