Assignment 2: Ray Tracing

Overview

What You Have to Do

• (1) Modify RayTrace(const char* fileName, int width, int height, int rLimit, float cLimit)  (in ray.[cpp/h]) to generate and cast rays from the camera's position through pixels to construct an image of the scene.
• (1) Implement the Group::intersect(Ray ray, IntersectionInfo& iInfo) (in group.[cpp/h]) to cast rays through scene-graph nodes. For now ignore the local transformation and simply compute the intersection properties for the closest intersection within the list of Shapes associated to the Group.
• (1) Implement the Sphere::intersect(Ray ray, IntersectionInfo& iInfo) (in sphere.[cpp/h]) method to compute ray intersections with a sphere.
• (2) Implement the Triangle::intersect(Ray ray, IntersectionInfo& iInfo) (in triangle.[cpp/h]) method to compute ray intersections with a triangle.
• (1) Modify  GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float  cLimit) (in ray.[cpp/h]) to return the color at the point of intersection using the ambient and emissive properties of the Material, and call this function in RayTrace(const char* fileName, int width, int height, int rLimit, floatcLimit) to compute the color at a point of intersection.
• (1) Implement:
• PointLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo)  (in pointLight.[cpp/h])
• SpotLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo) (in spotLight.[cpp/h])
• DirectionalLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo) (in directionalLight.[cpp/h])
in order to obatin the diffuse color contribution of the lights at the point of intersection.
• (1) Implement:
• PointLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in pointLight.[cpp/h])
• SpotLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in spotLight.[cpp/h])
• DirectionalLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in directionalLight.[cpp/h])
in order to obatin the specular color contribution of the lights at the point of intersection.
• (1) Implement:
• PointLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in pointLight.[cpp/h])
• SpotLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in spotLight.[cpp/h])
• DirectionalLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in directionalLight.[cpp/h])
• (1) Use the Light::getDiffuse, Light::getSpecular, and Light::isInShadow methods you implemented to modify GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float cLimit) so that the returned color takes into account the diffuse and specular contribution of the light sources. (Taking into account whether or not the point of intersection is in shadow with respect to a particular light.)
• (1) Modify the implementation of Group::intersect(Ray ray, IntersectionInfo& iInfo) (in group.[cpp/h]) to take into account the local transformation of the Group. (You can do this by using the transformation to convert the ray into object coordinates, computing the intersection, using the local transformation to convert intersection properties back into world coordinates, etc.)
• (1) Modify the implementation of  GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float cLimit) to recursively cast reflected rays at the point of intersection and add the reflected color contribution to returned color value.
• (1) Modify the implementation of  GetColor(Scene scene, Ray ray,IntersectionInfo iInfo, int rDepth, float cLimit) to recursively cast refracted rays through the point of intersection and add the refracted color contribution to returned color value. (For now, you should ignore the refraction index.)
• (1) Implement a jittered supersampling scheme to reduce aliasing by casting multiple rays per pixel, randomly jittered about pixel centers, and averaging the radiance samples.
• (2) Accelerate ray intersection tests with hierarchical bounding boxes. To do this you will have to:
• Implement BoundingBox::BoundingBox(Point3D* pList, int listSize) constructor. (This will create a box containing the specified list of points.)
• Implement BoundingBox::operator+ (BoundingBox b) method. (This will return a bounding box which contains the union of the two bounding boxes.)
• Implement the BoundingBox::intersect(Ray ray) method. (This will return the distance along the ray to the nearest point of intersection with the bounding box.)
• Implement the BoundingBox::transform(Matrix m) method. (This will return the bounding box containing the transformed -- no longer axis aligned -- bounding box.)
• Implement the Shape::getBoundingBox(void) for each of the Shape subclasses that you have implemented. This method will have to return the bounding box for that shape. Additionally, when modifying Group::getBoundingBox(void) you will have to accumulate the bounding boxes of all the child Shapes, transform them, find the bounding box of the transformed bounding box, store that and return it. (Note: When the parser is done reading the .ray file it automatically calls the Shape::getBoundingBox(void) method for the root node, so that if you have implemented this method for all of the subclasses of Shape, the bounding boxes are already in place to be used for intersection querries, and you do not have to reset them.)
• Group::intersect(Ray ray, IntersectionInfo& iInfo) to support testing ray intersection with the bounding box before testing for intersection with all child Shapes.
• Optimize the bounding box hierarchy so that when Group::intersect(Ray ray, IntersectionInfo& iInfo) is called, the Group checks all the bounding boxes first, chooses the one closest to the Ray, tests for intersection with the Shape corresponding to the bounding box and only tests those Shapes whose bounding box intersection is closer then the current closest intersection point.
• (2) Modify Triangle::intersect(Ray ray, IntersectionInfo& iInfo) (in triangle.[cpp/h]) to return the texture coordinates at the point of intersection and modify GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float cLimit)  to support texture mapping (with bilinear interpolation of texture samples).
• (1) Use the index of refraction and Snell's Law to calculate the correct direction of rays trasmitted through transparent surfaces and modify GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float cLimit)  appropriately.
• (1) Treat point/spot lights as having a finite 'area' and cast a collection of rays during shadow checking to generate soft shadows.  That is, if all shadows rays are blocked or unblocked we have zero or full lighting from the source in question just as before, but if a fraction of the shadow rays are blocked the light is only partially attentuated.  Something randomized and/or adaptive scheme should be used to avoid banding.
• (1) Implement the Box::intersect(Ray ray, IntersectionInfo& iInfo) (in box.[cpp/h]) method to compute ray intersections with a box.
• (1) Implement the Cylinder::intersect(Ray ray, IntersectionInfo& iInfo) (in cylinder.[cpp/h]) method to compute ray intersections with a cylinder.
• (1) Implement the Cone::intersect(Ray ray, IntersectionInfo& iInfo) (in cone.[cpp/h]) method to compute ray intersections with a cone.
• (1) Modify Sphere::intersect(Ray ray, IntersectionInfo& iInfo) (in sphere.[cpp/h]) to return the texture coordinates at the point of intersection (longitude and latitude) and modify GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float cLimit)  to support texture mapping (with bilinear interpolation of texture samples).
• (1) Implement procedural texture mapping with Perlin noise functions to create 3-D solid wood, marble, etc.
• (1) Implement bump mapping for either or both texturing schemes.
• (1) Implement depth of field camera effects.
• (1) Simulate real camera lens behaviour.  You must implement the procedure in this SIGGRAPH paper
• (2) Accelerate ray intersections with grid, octree or BSP spatial data structures.
• (?) Impress us with something we hadn't considered...

• (as listed above) implementing optional features,
• (1) submitting 3D models you constructed,
• (1) submitting images for the art contest,
• (1) submitting a .mpeg movie with a sequence of ray traced images resulting from a continuous camera path (e.g., use the

     makemovie command on the SGIs), and
• (2) winning the art contest.

Getting Started

• ray.[cpp/h] The code responsible for casting rays, calling intersection methods, computing colors, etc. etc. etc.
• shape.h The abstract base class that all shapes must implement
• group.[cpp/h] Code for the Shape subclass describing a scene-graph
• rayFileInstance.[cpp/h] Code for the Shape subclass describing the scene graph specified in a .ray file
• triangle.[cpp/h] Code for the Shape subclass describing a triangle
• sphere.[cpp/h] Code for the Shape subclass describing a sphere
• cone.[cpp/h] Code for the Shape subclass describing a cone
• cylinder.[cpp/h] Code for the Shape subclass describing a cylinder
• box.[cpp/h] Code for the Shape subclass describing a box
• line.[cpp/h] Code for the Shape subclass describing a line segment
• light.h The abstract base class that all l ights must implement
• pointLight.[cpp/h] Code for the Light subclass describing a point light
• directionalLight.[cpp/h] Code for the Light subclass describing a directional light
• spotLight.[cpp/h] Code for the Light subclass describing a spot light
• main.cpp This parses apart the command line arguments and invokes the raytracer
• scene.[cpp/h] Code for the classes that store environmental information, textures, materials, rayFiles etc.
• geometry.[cpp/h] Most of the code for the geometric manipulation you will need (matrix multiplication, vector addition etc.)
• boundingBox.[cpp/h] Code for defining bounding boxes.
• bmp.[cpp/h] Code responsible for reading and writing BMP files
• implemented.[cpp/h] Code defining a global flag that specifies if unimplemented methods should announce themselves when they are invoked.
• RayFiles/: Directory containing a variety of .ray files.
• tracer.dsp: Project file suitable for Visual C++ on Windows 2000 platform.
• Makefile: A Makefile suitable for UNIX platforms.
• viewer: A UNIX compiled ray-file viewer to look at .ray files. (Note that the code for this assumes that if you are looking at the front of the triangle the vertices are indexed in counter-clockwise order.)
• viewer.exe: A Windows 2000 comiled ray-file viewer to look at .ray files. (Note that the code for this assumes that if you are looking at the front of the triangle the vertices are indexed in counter-clockwise order.)

If you are developing on a UNIX machine, type make.

In either case an executable called tracer (or tracer.exe) will be created.

How the Program Works
The program takes in to mandatory arguments, the input (.ray) file name and the output file name (.bmp). It is invoked from the command line with:

    % image -src in.ray -dst out.bmp

Additionally, you can specify height, width, recursion depth and contribution limit as follows:

    % image -src in.ray -dst out.bmp -width w -height h -rlim r -clim c

What Has Not Been (Completely) Implemented

• RayTrace(const char* fileName, int width, int height, int rLimit, float cLimit)  (in ray.[cpp/h])
• GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float  cLimit) (in ray.[cpp/h])
• Sphere::intersect(Ray ray, IntersectionInfo& iInfo) (in sphere.[cpp/h])
• Sphere::GetBoundingBox(void) (in sphere.[cpp/h])
• Triangle::intersect(Ray ray, IntersectionInfo& iInfo) (in triangle.[cpp/h])
• Triangle::GetBoundingBox(void) (in triangle.[cpp/h])
• Group::intersect(Ray ray, IntersectionInfo& iInfo) (in group.[cpp/h])
• Group::GetBoundingBox(void) (in group.[cpp/h])
• Box::intersect(Ray ray, IntersectionInfo& iInfo) (in box.[cpp/h])
• Box::GetBoundingBox(void) (in box.[cpp/h])
• Cylinder::intersect(Ray ray, IntersectionInfo& iInfo) (in cylinder.[cpp/h])
• Cylinder::GetBoundingBox(void) (in cylinder.[cpp/h])
• Cone::intersect(Ray ray, IntersectionInfo& iInfo) (in cone.[cpp/h])
• Cone::GetBoundingBox(void) (in cone.[cpp/h])
• PointLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo)  (in pointLight.[cpp/h])
• PointLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in pointLight.[cpp/h])
• PointLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in pointLight.[cpp/h])
• SpotLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo) (in spotLight.[cpp/h])
• SpotLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in spotLight.[cpp/h])
• SpotLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in spotLight.[cpp/h])
• DirectionalLight::getDiffuse(Point3D cameraPosition, IntersectionInfo iInfo) (in directionalLight.[cpp/h])
• DirectionalLight::getSpecular(Point3D cameraPosition, IntersectionInfo iInfo) (in directionalLight.[cpp/h])
• DirectionalLight::isInShadow(IntersectionInfo iInfo, Shape* shape) (in directionalLight.[cpp/h])
• BoundingBox::BoundingBox(Point3D* pList, int pSize) (in boundingBox.[cpp/h])
• BoundingBox::operator+ (BoundingBox b) (in boundingBox.[cpp/h])
• BoundingBox::transform(Matrix m) (in boundingBox.[cpp/h])
• BoundingBox::intersect(Ray ray) (in boundingBox.[cpp/h])

What to Submit

• the complete source code with a Makefile,
• any *.ray files you created (optional),
• the .mpeg movie for the movie feature (optional),
• the images for the art contest (optional), and
• a writeup.

Make sure the source code compiles on the machines in the Friend Center. If it doesn't, you will have to attend to a grading session with a TA, and your grade will suffer.

Always remember the late policy and the collaboration policy.
 

Hints

• The Ray Tracing News is an invaluable resource for information. The archives contain information of everything you might want to know, and much more...
• Visit the POVRAY site,  home of a popular freeware raytracer.  Check out the links to the still comptetions and animated competitions for inspiration..
• For information about the barycentric coordinate triangle intersection test, check out Ray Tracing News issue RTNv5n3 which focuses on various polygon/ray intersection methods.
• check your progress by comparing your results with these results.
• Precept notes about class description and lighting equations is available here. (The page describing the getDiffuse method had an error in it and has since been removed.) If you want the power point version you can get that here: pdf.
ppt.

Notes

• The GetColor(Scene scene, Ray ray, IntersectionInfo iInfo, int rDepth, float  cLimit) (in ray.[cpp/h]) has been modified to take in the Ray and the maxDepth variable is not passed in. You should make the corresponding changes to the ray.cpp and ray.h files. (If you have not begun working on the assignment, the code on the arizona machine has been modified appropriately.)
• There seems to be some trouble with .bmp writing on Windows machines. Trying modifying the fopen command in main.cpp to: fopen(dst_filename,"wb") to open the file in binary mode.
• I have gotten a number of E-mails on this one: "What is the contribution limit and how do I use it?"

  Contribution limit is used to determine when the value of a color returned by casting secondary rays will be too small to be worth computing. Specifically, if you are casting specular (respectively transparent) rays, then before adding the color obtained by casting secondary rays, you will scale this color by the specular (respectively transparency) coefficient. Since the color coefficients must be between 0.0 and 1.0 the specular (respectively transparency) coefficient tells you in advance the upper bound on the brightness of the returned color. Thus if the specular (respectively transparency) contribution is less than the contribution limit you know that you do not need to send off secondary rays in the specular (respectively transparent) direction.

• In the Cone::read method, you should switch the order of reading so that the radius gets read in before the height.

FAQ