Program 3 2021: Rasterization
Partial Due: 11:59pm, Tuesday Oct 12
Final Due: 11:59pm, Tuesday Oct 19
Goal: In this assignment you will practice basic modeling and implement transforms and
lighting on 3D objects using the WebGL rasterization API.
Submission: Submit your assignment using this Google Form.
BASIC GRADING:
The main components of this programming assignment are:
• 5% Part 0: partial feedback
• 5% Part 1: properly turned in assignment
• 10% Part 2: render the input triangles, without lighting
• 25% Part 4: light the triangles
• 25% Part 5: interactively change view
• 5% Part 6: interactively select a model
• 25% Part 7: interactively transform the triangles
• Participation: Receive participation credit (outside of this assignment) for posting images
of your progress, good or bad, on the class forum!
General:
You may (optionally) work with one partner on this assignment. You should each turn in the
same code.
You will only render triangles in this assignment, described in the same sorts of JSON input files
used in the first. We will test your program using several different input files, so it would be wise
to test your program with several such files. The input files describe arrays of triangles using
JSON. An example input file resides at https://ncsucgclass.github.io/prog3/triangles.json. When
you turn in your program, you should use these URLs in hardcode as the locations of the input
triangle files — they will always be there. While testing, you should use a different URL
referencing a file that you can manipulate, so that you can test multiple triangle files. Note that
browser security makes loading local files difficult, so we encourage you to access any input
files with HTTP GET requests.
We provide a small shell in which you can build your code. You can run the shell here, and see
its code and assets here. The shell shows how to draw triangles using WebGL without any model
or view transform, and how to parse the input triangles.json file. It also shows how to use
animation callbacks to render multiple image frames.
The default view and light are as in the first assignment. The eye is at (0.5,0.5,-0.5), with a view
https://cgclass.csc.ncsu.edu/2021/09/program-3-2021-rasterization.html
https://forms.gle/cc5kgRNysvq6cvZs7
https://ncsucgclass.github.io/prog3/triangles.json
https://ncsucgclass.github.io/prog3/
https://github.com/NCSUCGClass/prog3
up vector of [0 1 0] and a look at vector of [0 0 1]. Locate the window a distance of 0.5 from the
eye, and make it a 1×1 square normal to the look at vector and centered at (0.5,0.5,0), and
parallel to the view up vector. With this scheme, you can assume that everything in the world is
in view if it is located in a 1x1x1 box with one corner at the origin, and another at (1,1,1). Put a
white (1,1,1) (for ambient, diffuse and specular) light at location (-0.5,1.5,-0.5).
This is an individual or partnered assignment, no exceptions. That said, we encourage you to
help one another. Feel free to suggest how other students might solve problems, and to help them
debug their code — just don’t write their code for them. The code you turn in should still be your
own or your single partner’s (except for the shell). This is a simple assignment, and should not
need other third party libraries. As always, if you are ever uncertain if the help you want to give
or the code you want to use is permissible, simply ask me or the TA. For information about how
to correctly submit, see this page on the class website.
Part 0: Partial feedback
You should turn in an “ugly,” incomplete version of your program by Friday October 12. If you
simply turn in a copy of our shell, you will get half credit (2.5%). If you actually do something to
visibly change the shell’s output, you will receive full marks (5%), and receive comments on
what you’ve done. For example, if you turn in a complete, first attempt at the assignment, we will
tell you in text what is working, and what isn’t, so you can raise your final score. We will not
otherwise grade the assignment at this point, only comment on it.
Part 1: Properly turned in assignment
5% of your assignment grade is just for correctly submitting your work! For more information
about how to correctly submit, see this page on the class website.
Part 2: Render the input triangles, without lighting
Use rasterization to render unlit triangles, giving each triangle its unmodified diffuse color (e.g,
if the diffuse color of the triangle is (1,0,0), every pixel in it should be red). You will have to use
vertex shaders to perform viewing and perspective transforms, and fragment shaders to select the
diffuse color. We recommend the use of the glMatrix library for creating these transforms.
Part 3: Light the triangles
Shade the triangles using per-fragment shading and the Blinn-Phong illumination model, using
the reflectivity coefficients you find in the input files. Use triangle normals during lighting. Your
fragment shaders will perform the lighting calculation.
Part 4: interactively change view
Use the following key to action table to enable the user to change the view:
• a and d — translate view left and right along view X
• w and s — translate view forward and backward along view Z
• q and e — translate view up and down along view Y
• A and D — rotate view left and right around view Y (yaw)
• W and S — rotate view forward and backward around view X (pitch)
http://cgclass.csc.ncsu.edu/p/good-turn-in.html
http://cgclass.csc.ncsu.edu/p/good-turn-in.html
http://glmatrix.net/
To implement these changes you will need to change the eye, lookAt and lookUp vectors used to
form your viewing transform.
Part 5: Interactively select a model
Use the following key to action table to interactively select a certain model:
• left and right — select and highlight the next/previous triangle set (previous off)
• space — deselect and turn off highlight
A triangle set is one entry in the input triangle array. To highlight, uniformly scale the selection
by 20% (multiply x y and z by 1.2). To turn highlighting off, remove this scaling. You will have
to associate a transform matrix with each triangle to maintain state, and apply this transform in
your vertex shaders. glMatrix will also be helpful here.
Part 6: Interactively transform models
Use the following key to action table to interactively transform the selected model:
• k and ; — translate selection left and right along view X
• o and l — translate selection forward and backward along view Z
• i and p — translate selection up and down along view Y
• K and : — rotate selection left and right around view Y (yaw)
• O and L — rotate selection forward and backward around view X (pitch)
• I and P — rotate selection clockwise and counterclockwise around view Z (roll)
Translate the model after you rotate it (so the model rotates around itself), and after the
highlighting scale (see above, so the model doesn’t translate as it scales).