NOTE: If you implement any bells or whistles you need to provide examples of these features in effect. You should present your extra credit features at grading time either by rendering scenes that demonstrate the features during the grading session or by showing images you rendered in advance. You might need to pre-render images if they take a while to compute (longer than 30 seconds). These pre-rendered examples, if needed, must be included in your turnin directory on the project due date. The scenes you use for demonstrating features can be different from what you end up submitting as an artifact.

Both Shirley's book and Foley, et al., are reasonable resources for implementing bells and whistles. In addition, Glassner's book on ray tracing is a very comprehensive exposition of a whole bunch of ways ray tracing can be expanded or optimized (and it's really well written). If you're planning on implementing any of these bells and whistles, you are encouraged to read the relevant sections in these books as well.

Remember that you'll need to establish to our satisfaction that you've implemented the extension! You should have test cases that clearly demonstrate the effect of the code you've added to the ray tracer. Sometimes different extensions can interact, making it hard to tell how each contributed to the final image, so it's also helpful to add controls to selectively enable and disable your extensions. In fact, we require that all extensions be disabled by default, with controls to turn them on one by one.

Here are some examples of effects you can get with ray tracing. Currently none of these were created from past students' ray tracers.

Implement an adaptive termination criterion for tracing rays, based on ray contribution. Control the adaptation threshold with a slider.

Implement antialiasing by supersampling and averaging down.

Modify your antialiasing to implement the first stage of distribution ray tracing by jittering the sub-pixel samples. The noise introduced by jittering should be evident when casting 1 ray per pixel.

Modify shadow attenuation to use Beer's law, so that the thicker objects cast darker shadows than thinner ones with the same transparency constant. (See Shirley p. 214.)

Include a Fresnel term so that the amount of reflected and refracted light at a transparent surface depend on the angle of incidence and index of refraction. (See Shirley p. 214.)

Implement spot lights (described in the Angel text). You'll have to extend the parser to handle spot lights but don't worry, this is low-hanging fruit.

Improve your refraction code to allow rays to refract correctly through objects that are contained inside other objects. You must put together a .ray file to demonstrate this effect.

Add code for interpolating the normal and material properties of a triangle's vertices. Don't forget to renormalize the interpolated normal. This is necessary for viewing some of the polymesh scenes such as sier.ray.

Add a menu option that lets you specify a background image to replace the environment's ambient color during the rendering. That is, any ray that goes off into infinity behind the scene should return a color from the loaded image, instead of just black. The background should appear as the backplane of the rendered image with suitable reflections and refractions to it. This is also called environment mapping. Click here for some examples.

Find a good way to accelerate shadow attenuation. Do you need to check against every object when casting the shadow ray? This one is hard to demonstrate directly, so be prepared to explain in detail how you pulled it off.

Deal with overlapping objects intelligently. While the skeleton code handles materials with arbitrary indices of refraction, it assumes that objects don't intersect one another. It breaks down when objects intersect or are wholly contained inside other objects. Add support to the refraction code for detecting this and handling it in a more realistic fashion. Note, however, that in the real world, objects can't coexist in the same place at the same time. You will have to make assumptions as to how to choose the index of refraction in the overlapping space. Make those assumptions clear when demonstrating the results.

Implement antialiasing by adaptive supersampling, as described in Foley, et al., 15.10.4. For full credit, you must show some sort of visualization of the sampling pattern that results. For example, you could create another image where each pixel is given an intensity proportional to the number of rays used to calculate the color of the corresponding pixel in the ray traced image. Implementing this bell/whistle is a big win -- nice antialiasing at low cost.

Implement more versatile lighting controls, such as the Warn model described in Foley 16.1.5. This allows you to do things like control the shape of the projected light.

Implement support for multithreaded anti-aliasing . This means splitting up the anti-aliasing amongst multiple processess. You'll definitely need to make use of the ThreadPool.cpp class. This is probably not too difficult if you have taken Operating Systems. If not, check out some info on Pthreads and threading here. We need to see some code and/or a convincing performance demonstration for credit.

Add texture mapping support to the program. To get full credit for this, you must add uv coordinate mapping to all the built-in primitives (sphere, box, cylinder, cone) except trimeshes. The square object already has coordinate mapping implemented for your reference. The most basic kind of texture mapping is to apply the map to the diffuse color of a surface. But many other parameters can be mapped. Reflected color can be mapped to create the sense of a surrounding environment. Transparency can be mapped to create holes in objects. Additional (variable) extra credit will be given for such additional mappings. The basis for this bell is built into the skeleton, and the parser already handles the types of mapping mentioned above. Additional credit will be awarded for quality implementation of texture mapping on general trimeshes.

Implement bump mapping (Watt 8.4; Foley, et al. 16.3.3). Check this out!

Implement solid textures or some other form of procedural texture mapping, as described in Foley, et al., 20.1.2 and 20.8.3. Solid textures are a way to easily generate a semi-random texture like wood grain or marble. Click here for a tutorial on making realistic looking marble using Ken Perlin's noise function.

Add some new types of geometry to the ray tracer. Consider implementing torii or general quadrics. Many other objects are possible here.

Add support for height-fields. Click here for a discussion on what they are and how they can be generated.

Extend the ray-tracer to create Single Image Random Dot Stereograms (SIRDS). Click here to read a paper on how to make them. Or, create 3D images like this one, for viewing with red-blue glasses.

for first, for each additional
Implement distribution ray tracing to produce one or more or the following effects: depth of field, soft shadows, motion blur, or glossy reflection (See Shirley 10.11, Watt 10.6, Glassner, chapter 5, or Foley, et al., 16.12.4).

Add some higher-level geometry to the ray tracer, such as surfaces of revolution, extrusions, metaballs, swept surfaces, or blend surfaces. You may have implemented one or more of these as a polygonal object in the modeler project. For the Raytracer, be sure you are actually raytracing the surface as a mathematical construct, not just creating a polygonal representation of the object and tracing that. Yes, this requires lots of complicated math, but the final results are definitely worth it (see Transparent Metaballs). Here is a really good tutorial on raytracing metaballs. For an additional bell, add texture mapping to your higher-level geometry. The texture mapping must look good in order to get credit for it!

Implement ray-intersection optimization by either significantly extending the BSP Tree implemented in the skeleton or by implementing a different optimization method, such as hierarchical bounding volumes (See Glassner 6.4 and 6.5, Foley, et al., 15.10.2).

Implement 3D fractals and extend the .ray file format to provide support for these objects. Note that you are not allowed to "fake" this by just drawing a plain old 2D fractal image, such as the usual Mandelbrot Set. Similarly, you are not allowed to cheat by making a .ray file that arranges objects in a fractal pattern, like the sier.ray test file. You must raytrace an actual 3D fractal, and your extension to the .ray file format must allow you to control the resulting object in some interesting way, such as choosing different fractal algorithms or modifying the base pattern used to produce the fractal.

Here are two really good examples of raytraced fractals that were produced by students during a previous quarter: Example 1, Example 2
And here are a couple more interesting fractal objects: Example 3, Example 4

Implement 4D quaternion fractals and extend the .ray file format to provide support for these objects. These types of fractals are generated by using a generalization of complex numbers called quaternions. What makes the fractal really interesting is that it is actually a 4D object. This is a problem because we can only perceive three spatial dimensions, not four. In order to render a 3D image on the computer screen, one must "slice" the 4D object with a three dimensional hyperplane. Then the points plotted on the screen are all the points that are in the intersection of the hyperplane and the fractal. Your extension to the .ray file format must allow you to control the resulting object in some interesting way, such as choosing different generating equations, changing the slicing plane, or modifying the surface attributes of the fractal.

Here are a few examples, which were created using the POV-Ray raytracer (yes, POV-Ray has quaternion fractals built in!): Example 1, Example 2, Example 3, Example 4. And, this is an excellent example from a previous quarter.

To get started, visit this web page to brush up on your quaternion math. Then go to this site to learn about the theory behind these fractals. Then, you can take a look at this page for a discussion of how a raytracer can perform intersection calculations.

Implement a more realistic shading model. Credit will vary depending on the sophistication of the model. A simple model factors in the Fresnel term to compute the amount of light reflected and transmitted at a perfect dielectric (e.g., glass). A more complex model incorporates the notion of a microfacet distribution to broaden the specular highlight. Accounting for the color dependence in the Fresnel term permits a more metallic appearance. Even better, include anisotropic reflections for a plane with parallel grains or a sphere with grains that follow the lines of latitude or longitude. Sources: Shirley, Chapter 24, Watt, Chapter 7, Foley et al, Section 16.7; Glassner, Chapter 4, Section 4; Ward's SIGGRAPH '92 paper; Schlick's Eurographics Rendering Workshop '93 paper.

This all sounds kind of complex, and the physics behind it is. But the coding doesn't have to be. It can be worthwhile to look up one of these alternate models, since they do a much better job at surface shading. Be sure to demo the results in a way that makes the value added clear.

Theoretically, you could also invent new shading models. For instance, you could implement a less realistic model! Could you implement a shading model that produces something that looks like cel animation? Variable extra credit will be given for these "alternate" shading models.  Links to ideas: Comic Book Rendering

Note that you must still implement the Blinn-Phong model.

Implement CSG, constructive solid geometry. This extension allows you to create very interesting models. See page 108 of Glassner for some implementation suggestions. An excellent example of CSG was built by a grad student here in the grad graphics course.

Add a particle systems simulation and renderer (Foley 20.5, Watt 17.7, or see instructor for more pointers).

Implement caustics by tracing rays from the light source and depositing energy in texture maps (a.k.a., illumination maps, in this case). Caustics are variations in light intensity caused by refractive focusing--everything from simple magnifying-glass points to the shifting patterns on the bottom of a swimming pool. Here is a paper discussing some methods. 2 bells each for refractive and reflective caustics. (Note: caustics can be modeled without illumination maps by doing "photon mapping", a monster bell described below.)

Here is a really good example of caustics that were produced by two students during a previous quarter: Example

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There are innumerable ways to extend a ray tracer. Think about all the visual phenomena in the real world. The look and shape of cloth. The texture of hair. The look of frost on a window. Dappled sunlight seen through the leaves of a tree. Fire. Rain. The look of things underwater. Prisms. Do you have an idea of how to simulate this phenomenon? Better yet, how can you fake it but get something that looks just as good? You are encouraged to dream up other features you'd like to add to the base ray tracer. Obviously, any such extensions will receive variable extra credit depending on merit (that is, coolness!). Feel free to discuss ideas with the course staff before (and while) proceeding!