GW-BASIC (Modern Cross-Platform Rewrite)

A modern, cross-platform rewrite of the classic GW-BASIC interpreter, implemented in C++20 with a real-time execution model and hardware-accelerated graphics.

This project aims to preserve the simplicity and spirit of GW-BASIC while providing a clean, extensible architecture suitable for modern systems.

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✨ Features

🧠 Language Support

• Line-numbered BASIC programs

• Immediate mode (REPL) + file execution

• Control flow:

  • IF ... THEN ... ELSE
  • GOTO, GOSUB, RETURN
  • FOR/NEXT
  • WHILE/WEND

• Variables:

  • Numeric + string
  • Arrays (DIM)
  • Default typing (DEFINT, DEFSTR, etc.)

• Expressions:

  • Arithmetic
  • Logical (AND, OR, NOT)

• Functions:

  • ABS, INT, LEN, VAL
  • SQR, SIN, COS, TAN, ATN
  • RND
  • String functions (LEFT$, RIGHT$, MID$, etc.)

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🎮 Real-Time Engine

• Frame-based execution model
• Non-blocking input (INKEY$)
• Engine tick integration
• Batch rendering for high-performance drawing
• Suitable for games and simulations

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🖥 Graphics

Rendering Backends

• Windows → Direct3D 11
• Linux → OpenGL (X11)
• Headless mode for testing / CI

Graphics API

• SCREEN
• CLS
• COLOR
• LOCATE
• PSET, LINE, CIRCLE
• PAINT, DRAW
• GET / PUT (graphics blocks)
• VIEW, WINDOW, PMAP
• PALETTE, PALETTE USING

Features

• Pixel canvas abstraction
• Palette remapping
• Viewport and world-coordinate transforms
• Hardware-accelerated presentation
• Automatic batching for performance

Examples

Here is example of graphics

tan(x^2 + y^2) = 1 graph example:

snake game example:

easter card example:

y=sin(x), y=cos(x) graphs:

norton commaner inspired example:

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📁 File I/O

• OPEN, CLOSE
• INPUT#, PRINT#, WRITE#
• LINE INPUT#
• EOF, LOF, LOC
• KILL, NAME, MKDIR, RMDIR

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🎹 Input

• INKEY$ (non-blocking)

• Keyboard input from:

  • Console
  • Native graphics window (Win32 / X11)

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🚀 Getting Started

Build

Requirements

• C++20 compiler
• CMake ≥ 3.16

Linux

mkdir build
cd build
cmake ..
cmake --build .

Windows (MSVC)

mkdir build
cd build
cmake ..
cmake --build . --config Debug

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▶️ Usage

Run interpreter (REPL)

gwbasic

Run BASIC file

gwbasic --file ./examples/snake.bas

Headless mode (no graphics window)

gwbasic --headless --file ./examples/snake.bas

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🧪 Example

Snake Game

gwbasic --file ./examples/snake.bas

Features:

• real-time gameplay
• keyboard control via graphics window
• hardware-accelerated rendering

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Math Plot

10 SCREEN 2
20 CLS
30 COLOR 15,0
40 CX = 320: CY = 100
50 SX = 0.03: SY = 0.03
60 FOR PY = 0 TO 199
70 FOR PX = 0 TO 639
80 X = (PX - CX) * SX
90 Y = (PY - CY) * SY
100 IF ABS(TAN(X*X+Y*Y)-1) < 0.05 THEN PSET (PX,PY), 10
110 NEXT PX
120 NEXT PY
130 END

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🏗 Architecture

Core Components

Interpreter

• Lexer → Parser → AST → Execution
• Line-numbered program storage
• Immediate + stored execution modes

Runtime

• Variable storage
• Array memory
• File handles
• Graphics state
• Engine tick integration

Graphics

• In-memory pixel canvas

• Platform-specific presenter:

  • D3D11 (Windows)
  • OpenGL (Linux)

• Batch rendering system

Engine Loop

• Cooperative execution
• Frame pacing (~60 FPS)
• Event pumping
• Input polling

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⚡ Performance Notes

• Rendering is batched, not per-pixel immediate

• Large plots are now significantly faster than naive implementations

• Still an interpreter → heavy numeric loops can be slow

• Prefer:

  • coarse stepping
  • analytical drawing (e.g., circles instead of brute-force)

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⚠️ Limitations

• Not a 100% GW-BASIC clone
• Graphics are portable abstractions, not exact hardware emulation
• Some legacy quirks are not implemented
• Floating-point math is modernized (not 8087-compatible)
• Performance depends on interpreter speed

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🛠 Roadmap

• Fixed-timestep VM scheduler
• More BASIC compatibility edge cases
• Improved parser tolerance
• Sound subsystem (PLAY, SOUND) improvements
• Better console emulation
• Optional SDL backend
• Debug / trace mode

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🤝 Contributing

Contributions are welcome.

Focus areas:

• language compatibility
• performance improvements
• platform backends
• test coverage

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📜 License

Under MIT license

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🎯 Vision

This project is not just a clone.

It’s a modern BASIC runtime:

• simple like the original
• powerful enough for real-time programs
• portable across platforms
• clean and extensible in design