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COMP 557  – Assignment 4
Ray Tracing
Competition image due before last class
Getting Started
In this assignment, you will write a raytracer. The sample code will get you
started with a json scene file parser and code to view the result and write a
PNG image file. You are free to make any modifications and extensions that
you please, to both the JSON format, parser code, and the ray tracing code;
however, your code should remain compatible with the simple examples
provided, and likewise, any changes you make must be well documented in
your readme file.
The provided code does not require OpenGL bindings, but requires GLM.
json scene description
The json file is organized as sequence of named materials, lights, cameras,
nodes, and geometry. The main scene is defined in the top-level node. In
general you will only need to have one node defined, but nodes can also be referred to within the scene graph
hierarchy as an instance (i.e., to help you reuse parts of the scene hierarchy multiple times). It is also possible to
define the scene with geometry directly, without using the node structure.
The scene nodes each have an associated transformation. The node definition can contain transformation
attributes: translation, rotation, and scale (and others if you choose to add them). These transformations are
applied, in this order, to build the node transformation (see Parser.createNodeTree and note how the transforms
are accumulated into the matrix hierarchicalShape.M). If you want a different order, consider making a subtree
with multiple nodes chained together. Scene nodes can also be different kinds of geometry (sphere, box, mesh,
instance). Finally, each node can also contain a list of child nodes, allowing a hierarchy of transformations and
geometry to be built.
Look at the provided examples to get a better idea of how the scene description files are organized. You may wish
to develop new test scenes and share them on the discussion board. However, note that you may need to
implement additional tags and attributes as you proceed through the objectives.
Provided Code
The scene to render must be provided as a command line argument, e.g.,
C:/Users/me/COMP557-L04/build> ./Debug/L04.exe ../resources/scenes/TorusMesh.json ../out/TorusMesh.png
and note that mesh files referenced within the json files must be specified relative to the build directory.
The main function will initialize the scene and call the scene render method to write the specified image file. You
should put your images into a directory COMP557-L04/out directory (i.e., to submit with your assignment). This render
method is a good place to start making changes to the code, but you will need to make lots of changes to many
classes, and make new classes on your own.
You’ve been provided with basic classes for defining a materials, lights, and nodes, but they do nothing except hold
loaded data. A Ray class and an IntersectionData have been defined for your convenience. You may wish (or need)
to change them. They are defined to allow the Shape interface to be defined. The sphere, box, plane, mesh, or any
other geometry (or node) that can be intersected will implement this interface. Here follows a brief description of
each file.
main
This is where the application starts and calls the render method.
Shape
This is the base class for objects in your scene that the rays intersect with. Each shape object has a
material, and an intersect method to check for ray-object intersection.
HierachicalShape
This is subclass of Shapes, and works as a group node to contain a collection of shapes. It also applies a
homogeneous transformation M to the ray before intersecting with all of its children.
AABB / Sphere / Mesh / Plane
These are subclasses of Shapes. Each have extra information relevant to the object type, such as radius
and center for Sphere. The class supports an arbitrary number of materials to be attached to a given shape,
however, for this assignment we assume the Plane holds two materials, and all others hold one. You are free
to play around with the number of materials you use for custom scenes. You need to implement the ray
intersection code in each!
Ray
This is a class for a Ray being cast into the scene. It is composed of a eye position and ray direction.
IntersectData
This object is passed alongside the ray and is used to store the extra information needed to color and shade
the pixel once an intersection is found. It stores information such as the material of the object hit, the
intersection point, and the normal.
Scene
The scene class contains information about all the intersectable objects, the lights, and extra scene
information such as the ambient light. This is where the rendering nested-for-loop lives .
Parser
This class is where the json file is parsed into a Scene object. This is already coded for you and will parse
the objects (spheres, boxes, planes, etc.), the scene information, the camera position, and material data. If
you want to add extra objects or parameters, for convenience or for bonus objectives, you will need
make changes in this file.
Ray Tracing Competition: best in show / le lapin d’or
There will be optional competition for images created with your raytracer. This is an opportunity to show off all the
features (e.g., extra features) of your ray tracer in an aesthetically pleasing novel scene that you design! To
participate, your assignment submission should have a ID-name-competition.json scene file for which you also
create the image ID-name-competition.png, where ID is your student ID and name is your name. Also include a
file ID-name-competition.txt containing a title and short description of the technical achievements and artistic
motivations for your entry. A small jury will judge submissions based on technical merit, creativity, and
aesthetics. Results will be announced on the last day of class. Note that you must submit these files to a different
assignment box on MyCourses the night before the last class.
Steps and Objectives
1. Generate Rays (1 mark)
The sample code takes you up to the point where you need to compute the rays to intersect with the scene.
Use the camera definition to build the rays you need to cast into the scene.
2. Sphere Intersection (1 mark)
The simplest scene, Sphere.json, includes a single sphere at the origin. Write the code to perform the
sphere intersection and set the colour to be either black or white depending on the result (i.e., don’t worry
about lighting in this first step).
3. Lighting and Shading (2 marks)
Modify your code so that you’re always keeping track of the closest intersection, the material, and the
normal. Use this information to compute the colour of each pixel by summing the contribution of each of the
lights in the json file. You should implement ambient, diffuse Lambertian, and Blinn-Phong
specular illumination models as discussed in class (note that the specular exponent, or
shinyness, is called hardness in the json file).
4. Plane (1 mark)
Add code to create an intersectable Plane object at y = 0 (i.e., a ground
plane). Planes may have two materials. In the case of a second material
being defined, the plane should be tiled with a checker board pattern.
Each square in the checkerboard should have dimension 1, and it should
be centered at the origin. The first material should be used in squares in
the +x +z and -x -z quadrants, while material2 should be used in the +x -z and -x +z quadrants. The
Plane.json (result shown at right) and Plane2.json demo scenes may serve as a useful test at this point.
5. Shadows (1 mark)
Modify your lighting code to compute a shadow ray, and test that the light is not occluded
before computing and adding the light contribution in the previous step. Make sure your
shadows work with multiple lights. The TwoSpheresPlane.json demo scene may serve as a
useful test at this point (see result shown at right).
6. Box (1 mark)
Add code to create an intersectable Box object. The box should be an axis aligned
rectangular solid, defined by the min and max corners of the box. You will find the
BoxRGBLights.json scene a useful test as it sets up different coloured lights in different axis
directions.
7. Hierarchy and Instances (1 marks)
Each scene node has a transform matrix to allow you to re-position and re-orientate objects
within your scene. The transformations defined in the scene nodes should transform the
rays before intersecting the geometry and child nodes, then transform the normal of the
intersection result returned to the caller.
The code in the HierachicalShape class implements the Shape interface and performs the
intersection test on all of its child nodes. If the material of the intersection result is null, then
the material of the scene node should be assigned to the result.
The BoxStacks.json scene is a useful test of your code when scenes are defined with a heirarchy and
instances.
8. Anti-aliasing and Super-sampling (1 mark)
Perform anti-aliasing of your scene by sampling each pixel more than once. The supersampling technique you use is up to you– uniform grid, stochastic pattern, or even
adaptive. Test your technique with the checkerboard plane in AACheckerPlane.json, and
note that the high frequency changes near the horizon are difficult to treat.
Note in addition to the samples member in scene, there is a boolean member to specify if you should jitter the
samples. Per pixel jittering (i.e., small amount of sub-pixel displacement of the ray direction) can help
replace aliasing with noise, which is helpful even in the absence of super-sampling!
9. Triangle Meshes (1 mark)
The provided code includes the polygon soup loader within the mesh class similar to that
used in the previous assignment. You can use this loader, or extend it, or write something
new to load the obj file specified in the mesh json nodes. Note that you do not have vertex
normals by default, so flat shaded triangles are fine (though Phong shading (interpolated
normals) would be nice). The scene file TorusMesh.json provides a simple example that
you may find useful for testing. Larger meshes, such as the bunny, will probably require
some acceleration techniques for practical rendering time. You can also try to run the code in Release mode
rather than Debug.
10. Create a Novel Scene (1 mark)
Create a unique scene of your own. Be creative. Try to have some amount of complexity to make it
interesting (i.e., different shapes and different materials). Your scene should demonstrate all features of your
ray tracer. Be sure to include your name and student number in the filename as described above in the
competition information so that it is unique in the class. That is presuming your novel scene is likewise the
scene that you will want to submit to the competition.
11. Remaining Marks and Bonus (4+ Marks to a max of 9)
Implement extra feature in your ray tracer to receive the remaining marks and bonus marks. A combination
of several additional features will be necessary to complete and then max out the bonus marks. To receive
full marks, your features must be clearly demonstrated to be correct with a test scenes, result image, and a
description in your read me file. For anything beyond the list below, the TA and professor will evaluate the
difficulty and assign additional marks accordingly. Be sure to document all your additional features in your
readme file.
Sampling and Recursion
Mirror reflection and or Fresnel Reflection (0.5 marks)
Refraction (0.5 marks)
Motion blur (0.5 marks simple motion, 1 mark complex motion)
Depth of field blur (1 mark)
Area lights, i.e., soft shadows (1 mark)
Path tracing (requires Area lights, 2 marks)
Geometry
Quadrics, easy! (0.5 marks)
Metaballs or other implicits (1.5 marks)
Bezier surface patches (2 marks)
Boolean operations for Constructive Solid Geometry (2 marks)
Textures
Environment maps, i.e., use a cube map or sphere map (1 mark)
Textured mapped surfaces or meshes (1 mark) with adaptive sampling and or mipmaps (1
more mark)
Perlin or simplex noise for bump maps, or procedural volume textures (1 mark)
Other
Multi-threaded parallelization (0.5 marks)
Acceleration techniques with hierarchical bounding volumes for big meshes, e.g., 100K
triangles or more (2 marks)
Acceleration techniques with spatial hashing and ray marching for big meshes (2 marks)
Something else totally awesome (discuss on boards, justify how many marks you want in the
readme)
Final Submission Format (read carefully)
Note that there is a different submission box in MyCourses for submitting your novel scene to the
raytracing competition!
Your submission should consist of your code, a detailed readme file, and a the set of json files and png files.
While you do need to have at least one novel scene, and you could probably create one image to show all of your
features at once, you (and the TAs) may find it useful if you create a variety of test scenes and associated images
that demonstrate any novel (and bonus) features of your raytracer. Your readme file must include a description
of each image/json pair. Use a zip file (only use zip) matching the directory structure of the provided code.
Note that the TA will also be running your code, but may not have the time to render all your tests (depending on
the efficiency or inefficiency of your implementation). Thus, a part of the evaluation of your assignment will be by
inspection of images in the submitted documents. Submitting an image that was not generated by your code is
considered cheating. It is largely on your honor that the images you show are yours (do not violate this trust).
Finished?
Great! Submit the requested files as a zip file (do not use a different type of archive) via MyCourses. Be sure to
include a readme file as requested. DOUBLE CHECK your submitted files by downloading them from MyCourses.
You can not receive any marks for assignments with missing or corrupt files!
Note that you are encouraged to discuss assignments with your classmates, but not to the point of sharing code
and answers. All code must be your own.

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