OpenGL Exercises

A collection of early OpenGL coursework (module 08235 Computer Graphics and UID, ~2003–2004), brought back to life. The original programs were written in Java against the now-defunct GL4Java binding and run as applets; this repo ports them to C# on OpenTK 4.x / .NET 8 so they build and run on a modern machine with a single command.

The rendering is still classic fixed-function, immediate-mode OpenGL — the goal was to preserve the teaching code exactly while replacing only the dead plumbing (windowing, GLUT/GLU helpers, texture loading). For the full story of what changed between the bindings — and the default-state gotchas (context profile, lighting, back-buffer alpha) — see docs/legacy-gl-to-opentk.md.

Ex 1 — GLUT wire cube	Ex 5 — viewports & objects	Ex 7.3 — solid lit teapot
Ex 8 — specular spheres	Ex 11 — perspective + camera	Ex 13 — texture mapping
Spiral sketch	Rose / petal curve	Interactive RGB triangle

Running

Requires the .NET 8 SDK (or newer) on a machine with an OpenGL-capable GPU.

cd src/OpenGLExercises

dotnet run                 # interactive menu of every exercise
dotnet run -- ex7_3        # run one exercise by id
dotnet run -- --list       # list every id
dotnet run -- spiral       # run a 2D sketch

Each exercise opens its own window and animates continuously. Close the window to return.

Headless capture / verification

Any exercise can be rendered to a PNG without interaction — used to verify the ports render correctly (and to produce the screenshots above):

dotnet run -- ex8 --capture out.png --frames 30

Exercises

OpenGL course (Ex 1–13)

A progression from a first wireframe primitive through lighting, materials, shading, projection, a camera and texture mapping.

id	Exercise
ex1	GLUT wire cube in an orthographic view
ex2_1	GLUT wire teapot
ex2_2	Cube built by hand from coloured line loops
ex4_1	The same cube in four quadrant viewports
ex4_2	Viewports that break the aspect ratio (distortion)
ex5	Four viewports, four primitives (cube / sphere / icosahedron / teapot)
ex6_1	First lit, smooth-shaded solid cube
ex6_2	Lit sphere using the default (grey) material
ex7_1	Flat-shaded lit sphere
ex7_2	Smooth-shaded lit sphere
ex7_3	Solid lit teapot
ex8	A sphere orbiting another, both with specular highlights
ex9	As Ex 8 but the light orbits the scene
ex10_1	Perspective set up directly with glFrustum
ex10_2	Perspective via gluPerspective
ex11	Perspective plus a camera (gluLookAt)
ex12_1	Surface normals — a lit diamond facing the light
ex12_2	The same diamond with a wrong normal (stays dark)
ex13	Texture mapping a PNG onto a fan of quads

2D sketches

Small parametric / interactive line drawings.

id	Sketch	Notes
spiral	Rotating Archimedean spirals	Left/Right arrows reverse the spin
square	Colour-cycling filled square
triangle	Interactive RGB triangle	Space spins it; R/G/B then click moves a vertex
cardioid	Cardioid r = a(1 − cos θ)	reconstructed*
sine	Sine wave	reconstructed*
petal	Rose curve r = cos(4θ)	reconstructed*
polar	Limaçon r = 0.5 + cos θ	reconstructed*

* The original source files for these four were corrupted to binary on disk, so they are faithful reconstructions from the curves' standard equations, in the same style as the surviving sketches.

Project layout

src/OpenGLExercises/
  Program.cs            launcher (menu / id / --capture)
  Core/
    ExerciseWindow.cs   GameWindow base — the GLAnimCanvas equivalent + capture
    Glut.cs             cube / sphere / icosahedron (GLUT had no OpenTK port)
    Teapot.cs           Utah teapot from Newell's Bézier patches
    Glu.cs              gluPerspective / gluLookAt
    Texture.cs          PNG -> GL texture (replaces GL4Java's PngTextureLoader)
    Png.cs              dependency-free PNG writer (for --capture)
    Catalog.cs          registry of every exercise
  Exercises/            Ex 1–13
  Exercises/Sketches/   the 2D sketches
docs/
  legacy-gl-to-opentk.md   binding migration + default-state notes

Credits

Original coursework by Richard Potter, module 08235 Computer Graphics and UID. Ported to C# / OpenTK while preserving the original behaviour.

The teapot control points (Core/Data/teapotrim.bpt) are Martin Newell's classic Utah teapot dataset.