Windowing System Architecture

Key Responsibilities

• Window Management: Creating, moving, resizing, minimizing windows
• Rendering: Drawing window contents to the screen
• Input Routing: Directing keyboard/mouse events to correct windows
• Layering: Managing window Z-order (which window appears on top)
• Effects: Transparency, shadows, animations (in modern systems)

1. WindowManager Class

Central controller managing all GUI windows. Handles window lifecycle, Z-ordering, and rendering coordination.

public static class WindowManager
{
    static List<Window> Windows = new List<Window>();
    
    public static void Add(Window window)
    public static void Remove(Window window)
    public static void BringToFront(Window window)
    public static void DrawAll()
    public static Window GetWindowAtPoint(int x, int y)
}

2. Window Base Class

Abstract base class for all window types (applications, dialogs, controls).

public abstract class Window
{
    public int X, Y, Width, Height;
    public string Title;
    public bool Visible;
    public bool Focused;
    
    public virtual void OnDraw(Canvas canvas)
    public virtual void OnMouseDown(int x, int y)
    public virtual void OnMouseMove(int x, int y)
    public virtual void OnKeyPress(char key)
}

3. Display Abstraction

Hardware abstraction layer supporting multiple graphics drivers (VMware SVGA, VBE/VESA).

public static class Display
{
    public static Canvas PrimaryCanvas;
    public static int Width, Height;
    
    public static void Initialize()
    public static void Clear(uint color)
    public static void DrawPixel(int x, int y, uint color)
    public static void SwapBuffers()
}

1. Application requests window update
2. WindowManager.DrawAll() called
3. For each visible window (back to front):
   - Window.OnDraw(canvas)
   - Render title bar, borders, content
4. Draw taskbar (always on top)
5. Display.SwapBuffers()
6. Visible on screen

// Main rendering loop
void RenderLoop()
{
    while (true)
    {
        // 1. Clear back buffer
        Display.PrimaryCanvas.Clear(DESKTOP_COLOR);
        
        // 2. Draw desktop wallpaper
        Desktop.Draw();
        
        // 3. Draw windows (back to front)
        foreach (var window in WindowManager.Windows)
        {
            if (window.Visible)
            {
                // Draw window frame
                DrawWindowFrame(window);
                
                // Let application draw content
                window.OnDraw(canvas);
            }
        }
        
        // 4. Draw taskbar (always on top)
        Taskbar.Draw();
        
        // 5. Draw mouse cursor
        Mouse.DrawCursor();
        
        // 6. Swap buffers (make visible)
        Display.SwapBuffers();
        
        // 7. Wait for next frame
        WaitForVSync();
    }
}

// Mouse click event routing
void OnMouseDown(int x, int y, MouseButton button)
{
    // 1. Find topmost window at click position
    Window target = WindowManager.GetWindowAtPoint(x, y);
    
    if (target != null)
    {
        // 2. Bring window to front
        WindowManager.BringToFront(target);
        
        // 3. Set keyboard focus
        WindowManager.SetFocus(target);
        
        // 4. Convert to window-relative coordinates
        int relX = x - target.X;
        int relY = y - target.Y;
        
        // 5. Deliver event to window
        target.OnMouseDown(relX, relY, button);
    }
    else
    {
        // Click on desktop
        Desktop.OnMouseDown(x, y);
    }
}

• Implement per-pixel alpha blending for true transparency
• Add window shadows using pre-rendered blur textures
• Optimize blitting with SIMD instructions or assembly
• Dirty rectangle tracking to avoid redrawing unchanged areas

• Implement interpolation system (easing functions)
• Add window minimize/maximize animations
• Fade in/out effects for windows and dialogs
• Smooth window dragging with motion prediction

• Implement OpenGL/Vulkan backend (major undertaking)
• Port rendering to GPU shaders
• Hardware-accelerated compositing
• Texture-based window rendering

• Virtual desktops/workspaces
• Live window thumbnails (Alt+Tab preview)
• High DPI scaling (fractional DPI support)
• Touch/gesture input support
• Window snapping/tiling (snap to screen edges)

Phase 1 improvements are achievable within the current architecture. Phase 3-4 would require significant architectural changes and native GPU drivers—a multi-year effort suitable for a dedicated research project or commercial OS development.