Jason Stredwick

jason.stredwick@gmail.com

Current Residence:
Bothell, WA 98011
me


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The source code and executable used to be available, but as I was cleaning it up I realized how much code I was using of Dr. Charles Owen and Sherri Goings. I felt that my contribution was not easily disentangled, so I am no longer providing the source code. The reason is I am unsure of the my rights to distribute that code. I do apologize, but you the executable and sample images are still available.

MonteCarlo.zip

Summary / Readme


Original raytracer was given to me from Sherri Goings.
The primary modifications took place in the following files:
CChildView.h
CChildView.cpp
MyRaytraceRenderer.h
MyRaytraceRenderer.cpp
and the resources to add a dialog for the number of sample rays

*Also, I modified and overloaded the AddLight functions. If you want to modify the Monte Carlo settings for a light, the more complicated AddLight functions must be used, which can't be used with the Opengl renderer.

All of my code should be outlined by ifdefs of MONTE_CARLO. I hope this easies the burden of incorporating my code. The following is an overview of the algorithms and design of this feature.

This is the information pertaining to the Monte Carlo raytracing used for CSE 891 Advance Computer Graphics, implemented by Jason Stredwick. Monte Carlo raytracing is the use of volumetric lights that have 3D surface. Using a stochastic sampling of surface points on a light, a more realistic blended lighting occurs

For this project, I used a simplied algorithm which I feel gives very similar results. All lights that can be used with the Monte Carlo technique must be sphere, or cones of light defined in terms of a sphere, light direction, and breadth angle. The simplification occurs in that I use a disc centered at sphere origin with a radius equal to the sphere radius, to represent the sphere. The disc is orientated such that the normal to the disc is the vector from the center to the surface point being lit. A random sampling from the surface of the disc is used to determine approximately how much, if any, of the light is blocked from the surface point by other objects.

The sampling functions were drawn from the website http://mathworld.wolfram.com/DiskPointPicking.html According to that website, the proper sampling formulas are

x = sqrt(radius) * cos(theta), y = sqrt(radius) * sin(theta)

where r is a random number from 0 to 1, and theta is a random number from zero to two pi. The reason given was that the sqrt(radius) relates to area of a circle which is where the samples originate from. Pictures illustrating the results showed that just using r, the samples clusted near the center of the circle.

Once the samples were determined, they needed to be converted to 3D points on the disc. A function was determined to generate a random "xy" coordinate system relative to the disc. Using these coordinate vectors, I was able to convert the 2D disc points to 3D disc points.

For each sample on the disc, a ray was cast from the surface point to the sample point. If the ray makes it to the sample point without intersecting something else along the way, it is given a value of 1, otherwise it is given a value of 0. A vector of these ones and zeros along with the light direction for each of the sampled points to the surface was recorded. For diffuse lighting, the dot product of each light ray by the surface normal was multiplied by each of the 0 or 1 associated with that ray. Summing all these values and dividing by the number of rays gives an approximation for the lighting of the surface point.

For directional lights, the same process occurs with one additional feature. When the sample is taken and the sampled light vector is computed. If the dot product of that vector with the light orientation is less than the cos of the sweep angle of the cone, then this vector is outside the cone of light and the contribution is set to zero. However, this is not fully functioning. I originally had a problem with the non-directional lights which was fixed by transforming the lights by transformation defined by the LookAt method. However, this did not solve my problem for directional lights, which I suspect is it is not properly transforming the orientation of the light. It does work, just the circle of light moves with viewer to some extent.

To really see the affects, you will need to change the light radius, and move the lights around. I currently have simple lighting that shows the basic features.