assignment_3 - 6.837 Introduction to Computer Graphics...

6.837 Introduction to Computer Graphics
Assignment 3:
Ray Tracing and Phong Materials
Due Wednesday October 1, 2003 at 11:59pm
This week, we add local and global illumination to our Ray Caster. Because
we cast secondary rays to account for shadows, reflection and refraction, we now
call it a Ray Tracer.
We clean up and improve shading calculation (local illumination). We define
an abstract material class and derive a Phong Material class that implements a
diffuse and a specular component (highlight).
You will encapsulate the high-level computation in a RayTracer class that
will be responsible for sending rays and recursively computing colors along them.
To compute cast shadows, you will send rays from the visible point to the
light source. If an intersection is reported, the visible point is in shadow and
the contribution from that light source is ignored. Note that shadow rays must
be sent to all light sources.
You will add reflection and refraction effects. For this, you need to send sec-
ondary rays in the mirror and transmitted directions, as explained in class. The
computation is recursive to account for multiple reflections and or refractions.
1 Tasks
• Implement an abstract Material class and derive a PhongMaterial class
that computes Phong shading.
• Update your intersection routines to return the Material of the intersected
object, instead of just a simple color.
• Create a new class RayTracer that computes radiance (color) along a ray.
Update your main function to use this class for the rays through each
pixel.
• Treat the case of multiple light sources by accumulating shading contri-
butions for all light sources.
• Compute cast shadows by sending rays toward the light sources.
1

• Compute perfect mirror reflection by sending rays recursively in the mirror
direction.
• Compute transparency effects by sending rays recursively in the refracted
direction.
• Provide a README.txt file that discusses any problems you encountered,
how long it took to complete the assignment, any extra credit work that
you did and how we can test the new features.
• Extra credit: semi-transparent shadows where the attenuation depends on
the distance traveled in the transparent object; nested refracting materials;
shadow ray acceleration using early termination and without returning the
normal and material; Fresnel reflection term; other BRDF models such as
Cook-Torrance or Ward; anisotropic BRDFs; solid textures.