Homework 06 Raytracer

KTH Stockholm
EECS :: CST
Introduction to Visualization and Computer Graphics

Homework assignment No. 06

Task 6.1: Raytracer: Intersections of a Ray with Geometric primitives 16 P
In this task you will have to complete a Raytracer by computing the intersections between a ray and some
geometric primitives. Use the workspace intersections.inv for this task. Once you press the Render button of
the Raytracer, you should see a blue screen together with a setup of the scene. Implement the following functions:
• For the sphere-ray intersection test (8 P)
bool Sphere::closestIntersectionModel(const Ray &ray, double maxLambda,
RayIntersection& intersection) const
• For the triangle-ray intersection test (8 P)
bool Triangle::closestIntersectionModel(const Ray &ray, double maxLambda,
RayIntersection& intersection) const
You will find these functions in the files sphere.cpp and triangle.cpp. If an intersection is found, the function
shall return true, else it shall return false. In case your function returns true, both functions should construct
objects of type RayIntersection and assign them to the parameter &intersection. You can refer to the
implementation of the Plane-Ray intersection in the file plane.cpp.
The constructor of the class RayIntersection takes the following parameters :
• const Ray &ray: constant reference of the Ray with which an intersection is found.
• std::shared ptr<const Renderable renderable: Reference in the form of a smart pointer to the Object
with which the intersection occurred. Use the term shared_from_this() here.
• const real lambda: Ray parameter where λ ∈ [0, maxLambda].
• const Vec3d &normal: constant reference to the normal direction at the point of intersection on the
Object’s surface.
• const Vec3d &uvw: ignore this and assign the Null Vector (0, 0, 0).
After you implement the aforementioned functions, the result should look like the image in Figure 1.
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Figure 1: Result of Task 1
Task 6.2: Raytracer: Phong Shading 8 P
Choose the workspace illumination.inv or Task 2 from the drop down. If you correctly implemented the
method for the Ray-Sphere intersection you should see an output similar to Figure 2.
The scene for this task consists of 3 point light sources, 4 spheres and a plane. All of these objects are assigned
a PhongMaterial material. Your task is to implement the Phong shading model.
In the file phongMaterial.cpp implement the function
Vec4d PhongMaterial::shade(const RayIntersection& intersection,
const Light& light) const
for the reflectance at the point of intersection between a ray and an object. At the moment a simple Lambertian
model is implemented with ideal diffuse reflection. You are supposed to implement the Phong model. The return
value should be color (red, blue, green, 1). If all goes well, you should see a result similar to Figure 3. Notice the
nice specular highlights of the point light sources on the surfaces of the spheres.
Task 6.3: Bonus: Sphere subtraction 8 EP
Raytracing allows us to perform complex operations on the geometry. Implement a special type of sphere that
gets substracted from other volumes in the same raytracing system as before. You are free to implement this
however you want in the raytracer. An example image can be seen in Figure 4 - a simplified version without
shadows and only rudimentary shading. The scene is called Bonus Task, the subtracting spheres are common
spheres so far. A few pointers:
• You might want to add this as a property directly to the sphere class or as a new object type in the
sphere.h/.cpp file. Either has its advantages.
• The actual raytracing is done in Scene.render().
• Feel free to change all the code you need - just make sure the other task scenes still work.
Make sure that you can have several such spheres, and the example looks correct. Phong shading and shadows
should work on it.
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Figure 2: Initial setup for Task 2
Figure 3: Task 2 result with Phong illumination model
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Figure 4: Example for sphere subtraction
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