CS 370: Assignment 1: Don Quixote

Written Questions Due Thursday, Sept 10th by 12:30/2:00 PM (in class) Submit a graded pdf to Canvas.

Program Due: Monday, Sept 14th by 11:59 PM Late assignments will be penalized 20 points per day. Follow the instructions below to upload to Marmoset

Getting Started

Download CS370_Assign01.zip, saving it into the assignment directory.

Double-click on CS370_Assign01.zip and extract the contents of the archive into a subdirectory called CS370_Assign01

Open CLion, select Open or Import from the main screen (you may need to close any open projects), and navigate to the CS370_Assign01 directory. This should open the project and execute the CMake script to configure the toolchain.

Written Questions

What are the main advantages and main disadvantages to generating images using the graphics pipeline?
Show that a rotation and a uniform scaling transformations (i.e. one where all the scale factors are identical) are commutative, i.e. that they can be applied in either order.

Hint: Given the general 4x4 matrices for each transformation

show that the appropriate matrix products commute, i.e. give the same result for both orderings.
Given the following set of vertices that define a square

Sketch a set of intermediate transformations to produce the following end result with proper size, orientation, and location. Give the final product of your particular transformation sequence using T(dx,dy) for a translation by dx and dy, R(θ) for a rotation (about the z axis) by angle θ, and S(sx,sy) for a scaling by sx and sy.

Sketch a set of intermediate transformations using only the upper left triangle vertices to produce the following end result with proper size, orientation, and location. Give the final product of your particular transformation sequence using T(dx,dy) for a translation by dx and dy, R(θ) for a rotation (about the z axis) by angle θ, and S(sx,sy) for a scaling by sx and sy.

Programming assignment

Write a program that draws a simple 2D “windmill” scene using OpenGL. The scene should include:

A shaded blue sky from top to bottom
A shaded green lawn from bottom to top
A windmill with brown walls and red roof
A fan with three blades (which can just use the sky color).
A shaded yellow sun from center to edge
<space> should start/stop the windmill fan spinning using time based animation
left mouse button should reverse the fan direction
<esc> should quit the program

Hints:

OpenGL renders scenes using a Painter’s Algorithm (at least for now). In this type of algorithm, the object that is rendered last will appear on top. This can be useful for making complicated shapes by simply overlapping simple shapes rather than using a single polygon with many vertices.

All the square and triangle shapes should be generated with the provided set of vertices. Use indexing to create the geometry from the vertices. Since the square is made from two triangles, you can draw a triangle by just using the first few indices when rendering.

Define separate color buffers for the different colors needed, e.g. gradient blue for the sky, gradient green for the grass, solid brown for the house, etc. Consider which colors should be assigned to which vertices to achieve the desired effect.

Use transformations to create all the geometry from the square (triangle) vertices. It may be helpful to sketch the scene on a sheet of graph paper to determine proper scale factors, rotation angles, and translation offsets. Note: Scalings and rotations are defined relative to the world coordinate origin not the object center.

For the sun, GL_TRIANGLE is not the only type of object that can be rendered in OpenGL. Chap 3 of OpenGL: Programming Guide discusses several other primitive types that can be used to render a set of vertices.

Use global variables to avoid magic numbers in the code, particularly for object transformations.

Don’t forget to register your callbacks, otherwise user interaction will have no effect.

Grading Criteria

The program MUST compile to receive any credit (so develop incrementally).

Create indexed square - 5 points
Create color buffers - 10 points
Draw shaded sky: 15 points
Draw shaded grass: 15 points
Draw solid house: 10 points
Draw fan: 15 points
Draw shaded sun: 10 points
Animation (keyboard, idle callbacks): 10 points
Creativity: 10 points

Be creative! For example, have the <space> act like a “puff” of air that starts the fan spinning but then gradually slows down until another <space> is pressed. Another option would be to add a keypress that changes the scene from day to night with the sun changing to a moon.

Compiling and running the program

You should be able to build and run the program by clicking the small green arrow towards the right of the top toolbar.

To quit the program simply close the window.

Submitting to Marmoset

At the top right of the CLion window, expand the drop down menu to change the configuration to MAKE_ZIP and click the green arrow

You may see a configuration dialog, simply click the Run button and Continue Anyway in the Change Configuration Settings popup dialog. This should generate a solution.zip file in the project root directory. Log into Marmoset and manually upload the solution.zip file to the assign01 submission.

You are responsible for making sure that your submission contains the correct file(s).