Computer Graphics Assignment 5: Cone and transformations 


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In this assignment, you will add a new primitive to our raytracer, a cone, and use transformation matrices to
position it in the scene. The ray-cone intersection should be performed in the local coordinate space of the
cone; therefore, you can limit yourself to implementing the ray-cone intersection for a very simple cone. The
transformation matrices will define the final size of the cone and its orientation.
Updated framework
Changes to the framework:
• The definition of the Object class contains now variables for three matrices:
– transformationMatrix representing the transformation of the object in the global coordinate
– inverseTransformationMatrix, the inverse of this transformation,
– and normalMatrix for the normal vectors transformation in the global coordinate system;
• The Object class now also contains the template of the function setTransformation which should
set the transformationMatrix and compute the other two matrices based on it;
• New header file, ”glm/gtx/transform.hpp”, of the GLM library is included for computing the transformation matrices;
• An empty definition of the Cone class.
The code is commented. Before continuing with the assignment, please familiarize yourself with the updates
and check the code for comments indicating the places which should be modified. As usual, the current
template is a solution for the previous codding assignment. Whether you want to start directly with the
provided template or continue from your solution to the previous assignment, it is up to you. In the latter
case, you are free to copy the above updates to the framework.
Useful functionality of the GLM library
• glm::mat4 type for 4 × 4 matrices;
• functions glm::inverse and glm::transpose allow you to easily compute the inverse and transpose of a given matrix,
• functions glm::translate, glm::scale, and glm::rotate enable an easy definition of translation, scaling, and rotation matrices;
• operation on matrices, vectors can be written as you would normally do on a paper, e.g., you can
directly multiply matrix by matrix or matrix by vector, as long as the dimensions agree;
• you can easily extend a vec3 by a homogeneous coordinate, multiply it by 4 × 4 and cast it back to
vec3, e.g., :
glm::vec3 newOrigin = matrix * glm::vec4(origin, 1.0); or
glm::vec3 newDirection = matrix * glm::vec4(direction, 0.0);
Exercise 1 [10 points]
Start by implementing the Cone class, such that it represents a
simple cone as shown in the image on the right. The cone is open,
it has 90 degrees opening angle, and the height equal 1. More
formally, the equation of the cone is given by x
2 + z
2 = y
y ∈ [0, 1].
To be able to transform the cone you should:
• finish the implementation of the function Object::setTransformation,
• implement the intersection with the cone in the local coordinate system of the cone, i.e., before performing the intersection, transform the ray to the local coordinate system using transformation matrices, and
then perform the intersection with the transformed ray. Afterwards, transform all the information to the
global coordinate system as discussed during the lecture. Please note that you do not have to take care
in this exercise about the uv-coordinates. But the intersection point, normal vector, and the distance to
the intersection have to be correctly defined in the final Hit structure.
Finally, add two cones to the scene. To this end modify the sceneDefinition function. Remember to set
the transformation matrix for each cone using the function setTransformation before adding each cone
to the collection of the objects.
You should add two cones as on the image above. The yellow cone should be highly specular. Its height is
12, and the radius of the bottom part is 3. The tip of the cone is at point (5, 9, 14). The green diffuse cone has
height 3 and radius at the base 1. The tip is located at point (6, −3, 7), and it is rotated around the z-axis such
that it lies with the side wall parallel to the ground. While you do not have to be very accurate to match the
material appearance from the image, please make the yellow cone highly specular such that the verification
of the normals and lighting computation is easier.
Exercise 2 [5 points]
Extend the implementation of the ray-cone intersection such that the cone is closed; i.e., add a disk that closes
the cone. The image above visualizes the closed green cone. You can use the Plane class for creating the disk.
Bonus exercise 3 [5 points]
Change the Sphere class such that the ray-sphere intersection is performed in the local coordinate system,
similarly as for the cone. The intersection routine should consider a simple sphere with radius one and the
center at the center of the local coordinate system of the sphere. The position and the size of each sphere
should be defined using transformation matrices. Make sure that the texture coordinates are defined in the
local coordinate system. Use the new version of the Sphere class for all the spheres in the scene. After you
achieve this, create an animation in which the textured sphere rotates around its axis and moves up and down
at the same time. If you correctly define the texture coordinates, the texture of the sphere will rotate with it.
For tips on how to create an animation, please check assignment 2.
You should submit one ZIP-file via iCorsi containing:
• one modified main.cpp,
• the final image generated using your code,
• 2-second video clip for the Exercise 3.
Additionally, in the comment to your submission please indicate which exercises you solved and what problems you encountered, if any.
Solutions must be returned on October 27, 2022 via iCorsi3