Hello Triangle - SDL3 with OpenGL Coordinates

A modern C++ demonstration project showcasing SDL3 graphics programming with proper coordinate system transformations and callback-based application architecture. USE vibe coding)

Project Structure

hello_triangle/
├── CMakeLists.txt          # Build configuration
├── main.cpp               # Main application source
└── README.md             # This file

Requirements

• SDL3 (latest development version)
• GLM (OpenGL Mathematics library)
• C++17 compatible compiler
• CMake 3.16+

Coordinate System Transformation

Transformation Function: update_transform_matrix

The core of the coordinate conversion is handled by this function:

void update_transform_matrix(AppState* state) {
    state->transform = glm::mat4(1.0f);
    
    // 1. First, shift (0,0) to the center of the window
    state->transform = glm::translate(state->transform, glm::vec3(
        state->window_width / 2.0f,   // X shift by half width
        state->window_height / 2.0f,  // Y shift by half height
        0.0f
    ));
    
    // 2. Then scale to window dimensions
    state->transform = glm::scale(state->transform, glm::vec3(
        state->window_width / 2.0f,   // X scale
        -state->window_height / 2.0f, // Y scale (negative for Y inversion)
        1.0f
    ));
}

Input Data: OpenGL Coordinate Vertices

The triangle vertices are defined in OpenGL normalized device coordinates:

glm::vec2 opengl_vertices[3] = {
    glm::vec2(0.0f,  0.5f),   // Top vertex
    glm::vec2(0.5f, -0.5f),   // Bottom-right vertex  
    glm::vec2(-0.5f, -0.5f)   // Bottom-left vertex
};

Vertex Colors

Each vertex has an associated color for gradient rendering:

SDL_FColor vertex_colors[3] = {
    { 1.0f, 0.0f, 0.0f, 1.0f },   // Red - Top vertex
    { 0.0f, 1.0f, 0.0f, 1.0f },   // Green - Bottom-right vertex
    { 0.0f, 0.0f, 1.0f, 1.0f }    // Blue - Bottom-left vertex
};

Features

• SDL3 Integration: Utilizes the latest SDL3 API with callback-driven application lifecycle
• OpenGL-style Coordinates: Implements a coordinate system similar to OpenGL with center at (0,0) and normalized ranges
• Hardware-Accelerated Rendering: Uses SDL_RenderGeometry for efficient triangle rendering
• Delta Time Calculation: Real-time frame timing for smooth animations and performance monitoring
• Cross-Platform: Compatible with Windows, macOS, and Linux
• Modern C++: Uses contemporary C++ features and smart memory management

Building

Linux/macOS

mkdir build && cd build
cmake ..
make
./HelloTriangleSDL3

Windows

mkdir build && cd build
cmake -G "Visual Studio 16 2019" ..
cmake --build . --config Release

Dependencies Installation

Ubuntu/Debian

sudo apt-get install libsdl3-dev libglm-dev cmake build-essential

macOS

brew install sdl3 glm cmake

Windows (vcpkg)

vcpkg install sdl3 glm

Architecture

The project demonstrates SDL3's callback-based architecture:

• SDL_AppInit: Initializes application state, window, and renderer
• SDL_AppEvent: Handles user input and window events
• SDL_AppIterate: Main rendering loop with delta time calculation
• SDL_AppQuit: Cleanup and resource management

Key Features Demonstrated

1. Window Management: Resizable window with automatic coordinate system updates
2. Coordinate Transformation: Mathematical conversion between OpenGL and SDL coordinate systems
3. Renderer Information: Automatic detection and logging of graphics backend
4. Input Handling: Keyboard (ESC to quit) and mouse input with coordinate conversion
5. Performance Monitoring: Real-time FPS and delta time calculation
6. Memory Management: Proper resource cleanup using RAII principles

Controls

• ESC: Exit application
• Window Resize: Automatically adjusts coordinate transformation matrix
• Mouse Click: Logs coordinates in both window space and relative to center

Performance

The application includes built-in performance monitoring:

• Real-time FPS counter
• Delta time calculation for frame-independent animations
• Efficient rendering using SDL's geometry API
• Automatic performance logging every second

Contributing

Contributions are welcome! Please feel free to submit pull requests or open issues for bugs and feature requests.