GFX-13

Version 1.1 (x86 Assembly)

A VGA Mode 13h (320x200, 256 colors) 2D graphics library for demo coding, written in x86 assembly language back in the 90s.

Features:

• Fast clipping
• Putting and getting pixels.
• Wireframe primitives.
• Filled primitives.
• Image blitting (Get image and scale image added to version 2.0)

		3D codded with my M3DE graphics engine.

Version

Version	Language	Toolchain
v1.1	Pure 80x86 assembly	TASM (For GFX-13 library) Borland Turbo C++ 3.1 (For test programs)
v2.1	Upgraded version written in C with inline assembly	Borland Turbo C++ 3.1

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 );

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.

    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 Assembler (TASM) 3.x and Borland C++ 3.1 on PATH.

Assembly + Test Programs

cd test
build.bat

Assembles gfx13.asm with TASM (/ml for case-sensitive C linkage), then compiles and links 8 test programs with BCC.

Clean

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

Test Suite

The library includes 8 visual test programs:

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-v1-ASM/
├── gfx13.asm           Library source (pure TASM assembly)
├── gfx13.h             C-callable header (18 functions)
├── images/             Screenshot captures
│   └── capture/        Demo and test screenshots
└── test/               8 visual test programs
    ├── build.bat       Build script (TASM + 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

This project is provided as-is for educational and archival purposes.