OpenGL Computer Graphics Labs

📚 Course Information

Course: Computer Graphics
Institution: National Taipei University of Technology (NTUT / 臺北科技大學)
Academic Year: 113 (2024-2025)

This repository contains lab assignments for the Computer Graphics course, implementing various OpenGL rendering techniques and algorithms.

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🧪 Lab Descriptions

Lab 1 - 3D Cube Transformations & Orbital Motion

Fundamental 3D graphics exercise implementing cube transformations:

• Custom rotation, translation, and scaling matrices implementation
• Arbitrary axis rotation using user-defined vectors
• Orbital animation around custom axes
• Colored cube rendering with six distinct faces
• Interactive keyboard controls for real-time transformations
• XYZ coordinate axes visualization
• gluLookAt camera setup for 3D viewing

Lab 2 - Interactive Grid System

A fundamental 2D graphics exercise implementing an interactive grid system with:

• Dynamic grid rendering with adjustable dimensions (10×10, 13×13, 15×15)
• Mouse click detection for selecting and filling grid cells
• Right-click context menu for dimension switching
• Coordinate system transformation between window and OpenGL coordinates

Lab 3 (Mid-term) - 3D OBJ Model Viewer

A comprehensive 3D model viewer application featuring:

• OBJ file parsing and rendering (supports multiple models: teddy, gourd, octahedron, teapot)
• Multiple rendering modes (wireframe, solid, etc.)
• Complete camera control system (pan, rotate, zoom)
• Model transformation controls (rotate, translate)
• Automatic bounding box calculation and model fitting
• 3D vector math utilities for graphics operations

Lab 4 - Midpoint Line Drawing Algorithm

Implementation of the Midpoint Line Algorithm for line rasterization:

• Support for all eight octants (0° - 360°)
• Region-based color coding for different line slopes
• Visual demonstration of pixel selection during line drawing
• Interactive point selection via mouse clicks

Lab 5 - Polygon Filling with Half-Space Method

Polygon rasterization using the Half-Space (Edge Function) Method:

• Interactive polygon vertex input
• Inside/outside testing using cross product (edge functions)
• Visual representation of filled polygons with color coding
• Extension of the midpoint line algorithm for polygon boundaries

Lab 6 - Animated Polygon Filling

Enhanced polygon filling with real-time animation:

• Timer-based animation for visualizing the fill process
• Step-by-step cell filling demonstration
• Improved understanding of rasterization algorithms
• Interactive polygon creation with animated results

Lab 7 - Scanline Polygon Fill Algorithm

Implementation of the Scanline Fill Algorithm with advanced features:

• Edge Table (ET) and Active Edge Table (AET) construction
• Gradient color filling based on X/Y position (red-green horizontal, blue-yellow vertical)
• Animated scanline visualization with step-by-step filling
• Extreme point highlighting (gold color) for each scanline
• Proper handling of horizontal edges and edge intersections
• Support for arbitrary convex/concave polygon input
• Interactive polygon creation with mouse clicks

Lab 8 - Icosahedron Sphere Subdivision & Shading

3D sphere rendering using icosahedron subdivision:

• Recursive triangle subdivision for smooth sphere approximation
• Adjustable subdivision levels (0-5) with +/- keys
• Three viewport display: Flat Shading | Smooth Shading | Subdivided
• Right-click menu for wireframe/fill mode switching
• OpenGL lighting and material configuration
• Arrow keys for interactive model rotation

Lab 9 - Planar Shadow Projection (Jet Model)

Implementation of planar shadow mapping technique:

• 3D jet aircraft model with detailed geometry (nose, body, wings, tail)
• Shadow matrix calculation based on light position and ground plane
• Four switchable light positions (keys 1-4 or F1-F4)
• Green gradient ground plane for depth perception
• Real-time jet rotation with arrow keys
• Yellow sphere indicator for current light position
• Custom 3D math library (vectors, matrices, plane equations)

Lab 10 (folder: lab10) - Textured Scene with Robot Animation & Shadows

Advanced 3D scene with texture mapping and planar shadows:

• TGA texture loading (grass ground, wood, orb textures)
• Animated 3D robot character with hierarchical transformations
• Articulated limb animation (arms and legs swing with sine wave)
• Orbiting textured sphere around the robot
• Planar shadow projection using shadow matrix
• Stencil buffer for proper shadow rendering (semi-transparent shadows)
• Camera movement controls (GLFrame with arrow keys)
• Real-time animation with timer functions (33ms interval)
• Pause/resume animation with 'P' key

Lab 11 (folder: lab11_final) - OBJ Model Loader with Texture Mapping

Comprehensive 3D model loading and rendering system:

• OBJ file parsing for complex 3D models (Viper, castle, fish, human, whale, etc.)
• OpenCV-based texture loading (JPG/PNG format support)
• Multiple texture types (background, cartoon water, galaxy, grid, orange skin)
• GLU tessellator for non-triangular polygon faces
• Normal and UV coordinate handling from OBJ files
• Dynamic model and texture file discovery from folders
• Shadow projection for loaded models

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📋 Requirements (macOS)

Dependencies

Dependency	Description
OpenGL	Core graphics library (pre-installed on macOS)
FreeGLUT	OpenGL Utility Toolkit for window management

Installing Dependencies

Install FreeGLUT via Homebrew:

brew install freeglut

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🛠️ Build & Run (macOS)

Compilation

gcc lab2.cpp -o lab2 -I/opt/homebrew/include -L/opt/homebrew/lib -lglut -framework OpenGL

Run

./lab2

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📁 File Structure

opengl_lab/
├── README.md
├── lab1.cpp              # 3D Cube Transformations & Orbital Motion
├── lab2.cpp              # Interactive Grid System
├── lab3_mid.cpp          # 3D OBJ Model Viewer (Mid-term)
├── lab4.cpp              # Midpoint Line Algorithm
├── lab5.cpp              # Half-Space Polygon Fill
├── lab6.cpp              # Animated Polygon Fill
├── lab7.cpp              # Scanline Polygon Fill Algorithm
├── lab8.cpp              # Icosahedron Sphere Subdivision
├── lab9.cpp              # Planar Shadow Projection (Jet)
├── lab10/
│   ├── lab10.cpp         # Textured Robot Scene with Shadows
│   ├── grass.tga         # Ground texture
│   ├── wood.tga          # Wood texture
│   └── orb.tga           # Sphere texture
└── lab11_final/
    ├── lab11.cpp         # OBJ Model Loader
    ├── model/
    │   ├── Viper.obj     # Spaceship model
    │   ├── castle.obj    # Castle model
    │   ├── fish.obj      # Fish model
    │   ├── human1.obj    # Human model 1
    │   ├── human2.obj    # Human model 2
    │   ├── human3.obj    # Human model 3
    │   ├── whale.obj     # Whale model
    │   └── ...           # Other OBJ models
    └── texture/
        ├── background.jpg
        ├── cartoon_water_blue.jpg
        ├── galaxy_blue_red.jpg
        └── ...           # Other textures

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⌨️ Common Controls

Key	Action
W/A/S/D	Model/Object rotation
Q/E	Z-axis rotation
I/J/K/L	Model translation
+/-	Zoom in/out
Arrow Keys	Camera/View rotation
ESC	Exit program
Right-click	Context menu (where applicable)

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📖 Topics Covered

• 2D/3D Coordinate Systems
• Rasterization Algorithms (Line, Polygon)
• Geometric Transformations (Translation, Rotation, Scaling)
• 3D Model Loading and Rendering
• Camera and View Transformations
• Lighting and Shading
• Texture Mapping
• Shadow Techniques
• Tessellation and Subdivision Surfaces

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📝 License

This repository is for educational purposes as part of the NTUT Computer Graphics course curriculum.