GFX-13

Version 2.1 (C with inline Assembly)

   

   

   

3D coded with my M3DE graphics engine.

A VGA Mode 13h (320x200, 256 colors) 2D graphics library for old-school demo coding, written in C with Borland Turbo C++ inline assembly.

This is the upgraded version of my original pure assembly mode 13h graphics library (GFX-13 v1). I wrote this version to make it a bit easier to maintain and integrate into C++ programs. GFX-13 v2 adds two new image blitting functions (GetImage, ScaleImage) and is backward compatible with GFX-13 v1.

📑 Table of Contents

• 🏷️ Versions
• ✨ Features
• 🧩 API
• 🚀 Usage
• 🔨 Build
• 🧪 Test Suite
• 📂 Repository Structure
• ⚙️ Technical Details
• 📄 License

🏷️ Versions

Version	Language	Toolchain
v1.1	Pure x86 assembly	TASM
v2.1	Upgraded version written in C with inline assembly	Borland Turbo C++ 3.1

✨ Features

• Fast clipping
• Putting and getting pixels.
• Wireframe primitives.
• Filled primitives.
• Image blitting and scaling.

🧩 API

// Mode Functions

void SetMode13      ( void );
void SetTextMode    ( BYTE rows );
BYTE GetTextMode    ( void );

// Palette and Clipping Functions

void SetPalette     ( BYTE col, WORD count, WORD segment, WORD dataOffset );
void SetClipping    ( int x0, int y0, int x1, int y1 );

// Screen Functions

void ClearScreen    ( BYTE col, WORD dest );
void FlipScreen     ( WORD source, WORD dest );
void WaitRetrace    ( void);

// Pixel Functions

void PutPixel       ( WORD x, WORD y, BYTE col,  BYTE clip, WORD dest );
BYTE GetPixel       ( WORD x, WORD y, BYTE clip, WORD source );

// Unfilled Primitives

void Line           ( WORD x0, WORD y0, WORD x1, WORD y1, BYTE col, BYTE clip, WORD dest );
void Triangle       ( WORD x0, WORD y0, WORD x1, WORD y1, WORD x2,  WORD y2,   BYTE col, WORD dest );
void Rectangle      ( WORD x0, WORD y0, WORD x1, WORD y1, BYTE col, WORD dest );
void Quad           ( WORD x0, WORD y0, WORD x1, WORD y1, WORD x2,  WORD y2,   WORD x3, WORD y3, BYTE col, WORD dest );

// Filled Primitives

void FillRectangle  ( WORD x0, WORD y0, WORD x1, WORD y1, BYTE col, WORD dest );
void FillTriangle   ( int  x0, int  y0, int  x1, int  y1, int  x2,  int  y2, BYTE col, WORD dest );
void FillQuad       ( int  x0, int  y0, int  x1, int  y1, int  x2,  int  y2, int  x3,  int  y3, BYTE col, WORD dest );

// Blitting Functions

void PutImage       ( WORD x,  WORD y,  WORD xs, WORD size, BYTE mask,      WORD source_seg, WORD source_offs, WORD dest );
void GetImage       ( WORD x0, WORD y0, WORD x1, WORD y1,   WORD source,    WORD dest_seg,   WORD dest_offs );
void ScaleImage     ( WORD x0, WORD y0, WORD x1, WORD y1,   WORD source_xs, WORD source_ys,  BYTE mask, WORD source_seg, WORD source_offs, WORD dest );

All dest and source parameters are 16-bit segment addresses (e.g., 0xA000 for VGA video memory).

🚀 Usage

#include "gfx13.h"

#define VGA 0xA000

int main ( void )
{
    // Set mode-13h.

    SetMode13 ();

    // GFX-13 function calls (Version-2).

    ClearScreen  ( 0, VGA );
    FillTriangle ( 160, 10,  10,  190, 310, 190, 4, VGA ) ;
    Line         ( 0,   0,   319, 199, 15,  1,      VGA );
    PutPixel     ( 160, 100, 14,  1,                VGA);

    // Return to text mode.

    getch       ();
    SetTextMode ( 25 );

    // Exit program.

    return 0;
}

🔨 Build

Requires DOSBox (or real DOS) with Borland Turbo C++ 3.1 on PATH.

cd test
build.bat

Compiles src/gfx13.c and links 8 test programs with BCC (-1 for 80186 mode, -P for C++ mode).

Clean

Run clean.bat from the test/ directory to remove build artifacts.

🧪 Test Suite

8 visual test programs are included:

Test	Description
testpix	Pixel drawing, reading, and screen clearing
testline	Line drawing with Bresenham's algorithm
testrect	Outline and filled rectangles
testtri	Outline and filled triangles
testquad	Outline and filled quadrilaterals
testimg	Image blitting with PutImage
testpal	VGA palette manipulation
testclip	Clipping rectangle tests

Each test program displays multiple screens. Press any key to advance between screens.

📂 Repository Structure

GFX13-v2-C/
├── src/              Library source
│   ├── gfx13.c       Library source (C with inline assembly)
│   └── gfx13.h       C-callable header (20 functions)
│
├── images/           Screenshot captures
│   └── capture/      Demo and test screenshots
│
└── test/             8 visual test programs
    ├── build.bat     Build script (BCC)
    ├── clean.bat     Clean build artifacts
    ├── testutil.h    Shared test utilities
    ├── testpix.c     Pixel drawing and reading
    ├── testline.c    Line drawing
    ├── testrect.c    Outline and filled rectangles
    ├── testtri.c     Outline and filled triangles
    ├── testquad.c    Outline and filled quads
    ├── testimg.c     Image blitting
    ├── testpal.c     VGA palette manipulation
    └── testclip.c    Clipping rectangle tests

⚙️ Technical Details

• Target: 80186+ real mode, small memory model
• Resolution: 320x200, 256 colors (VGA Mode 13h)
• Pixel offset: y * 320 + x computed via shifts as y*256 + y*64 + x
• Line clipping: Cohen-Sutherland algorithm
• Filled polygons: Scanline rasterization with 16.16 fixed-point DDA edge walking
• Palette streaming: REP OUTSB to VGA DAC (requires 80186+)

📄 License

Released under the MIT License — Copyright © 1991 Rohin Gosling.