In article <39acb150$1@news.povray.org>, "Mathias" 
<Mat### [at] dlrde> wrote:

> Then please tell me how povray raytraces a scene ? I dont know it.......

Hmm, I will try my best...at the most basic level, a raytracer works 
this way:

For each pixel, it determines the direction and starting point of a line 
going from that pixel to the portion of the scene visible from that 
pixel. This is a "ray", an infinite line with a starting point and 
direction. It then tests the ray against all the objects in the scene, 
finding all(or a large number of) of the intersections it makes with 
object surfaces. It usually does this by solving an equation. The 
closest intersection found is taken as the first one, and the color of 
the texture at that point is calculated.

To calculate reflections, it then determines a new direction for the 
ray, based on the surface normal at the intersection point, and sets the 
origin to the intersection point. It then "traces the ray" again, much 
like the first ray, to get the contribution reflection makes to the 
color of the surface. Refraction is done similarly, except the ior value 
is also taken into account and a different calculation is used for 
getting the new ray direction. Lighting is done by tracing a ray toward 
a light source, and calculating the effect of transparent objects 
between the object and light source on the light, or producing a shadow 
if an opaque object is encountered.

Most raytracers use recursion, and go several levels deep into the 
scene, so a ray can reflect or refract several times before stopping. In 
POV, the maximum level is controlled by the max_trace_level keyword in 
global_settings.

The exact way POV does things is much more complex, and follows a pretty 
convoluted path through several source files, depending on the exact 
features used and the portion of the scene currently being calculated, 
and unfortunately, there is very little documentation on the source code.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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