Project 3 Help Session

This session is to help you get started with the third project: a raytracer.

Starting the Project

After copying the files from course web page, the ray trace program can be run by typing double clicking the .dsw project file and building the project in MSVC. This raytracer reads files with the .out file extension. Load a scene such as simple.out and hit the render button to see how the basic program works. Note that the size of the render window is adjustable. The smaller your window, the quicker the scene will render. The sphere and box in the scene should appear as flat disks when rendered, since the routines that compute the color of each pixel have been gutted for your educational benefit.

Useful Files

This program has quite a few source files associated with it, but don't be alarmed, because most of your of your work on this project will be concentrated in only a few files. In fact, all of the required extensions require modifying only the Shade() function in Raytrace.cpp. Here are a list of some of the most important of the files:

Raytrace.{cpp,h} Here's where all the required extensions will be added.

Intersect.{cpp,h} These routines cast rays and determine intersection points with various objects. To add a more general type of refraction, you will need to edit these files.
SceneIO.{cpp,h} These files define the scene. You shouldn't have to make changes here.

Shade() Function

The function in which you will implement all the required extensions is the Shade function in Raytrace.c:

Void
Shade(SceneIO *scene, int level, float weight, Vector3f P, Vector3f N,
	Vector3f I, struct IsectType *intersect, Vector3f color,
RTParameters* g_params);

This function calculates the color of an intersection point of a ray that is cast into the scene.

scene contains information about the lights and objects
level indicates the current level of recursion
weight is a term used with the recursive reflection and transmission rays
P is the intersection point with an object
N is the normal to the surface at the point P
I is the incident ray from the point P
intersect contains information about the intersection point Note: When calculating refraction, prevIndex indicates the index of refraction in the medium the ray is coming from and nextIndex the index of refraction in the medium the ray is entering
color is the color of the object at the intersection point which you will be calculating
g_params is the struct which contains the information for the recursion.

MaterialIO

The struct MaterialIO contains information about the properties of an intersection point on an object. The comments following the elements of the struct contain the symbols used in the Phong shading model presented in class.

typedef struct MaterialIO
{
	Color3f diffColor;  /* Diffuse color: kd */
	Color3f ambColor;   /* Ambient color: ka */
	Color3f specColor;  /* Specular color: ks */
	Color3f emissColor; /* Emissive color- do not need for assignment */
	float shininess;    /* Shininess: ns */
	float ktran;        /* Transparency: ktran */
} MaterialIO;

Ray

This struct contains the information about the ray cast by the intersection routine.

typedef struct Ray
{
	Point3f P;         /* point of origin of the ray */
        Point3f D;         /* direction ray is traveling */
} Ray;

RTParameters

This struct contains information used for recursion.

typedef struct RTParameters
{
	float rayeps;      /* epsilon value for ray intersections */
	float minweight;   /* min weight to keep tracing a ray - 
		Note: this may be used to implement one of the whistles */
	float maxlevel;    /* max number of tracing levels - 
		Note: max level can be 4 for the basic assignment */
} RTParameters;

Additional Information

When you are viewing scenes rendered with your solution, the scenes may appear washed out. Scale the factors in your code until the ray traced image looks roughly similar to the sample images given by running the solutions. (However the images don't have to be an exact match in color. Just make sure that the shadows, reflections and tranmissions are falling in the right places).
For (semi-)transparent surfaces, you should probably multiply the diffuse and ambient terms by (1-ktran). Otherwise, the diffuse and transmitted rays will add up and the surface will become washed out.
For the basic assignment (without any bells or whistles for refraction), the refractive index may be set to 1.5.
For ns, use shininess*128 (where shininess is the scene's shininess output between 0 and 1.)
For attenuation of light sources, use the attenuation equation presented in class with a =.01, b = .1, and c = .25. If your results don't look satisfactory, feel free to play with this parameter. Note: Secondary rays (reflected and transmitted) are not attenuated.
Happy Raytracing

Send questions or comments about the help session and handouts to Doug (dougz@cs) or Michael(maucoin@cs).