VGA Mode X Scrolling

This project aims to be a template for the following:

• Setting up the tweaked VGA Mode 13 known as Mode X that allows for a 320x240 display with square pixels under DOS
• Routines for quickly blitting bitmap images from main memory to VRAM
• Smooth hardware scrolling across an infinite-sized map

Requirements

• Open Watcom C/C++ Version 2.0 (Windows or Linux)
• DOS-based environment (MS-DOS, FreeDOS, DOSBox) to run the builds
• DOS/32 or DOS4GW 32-bit DOS extender

How To Build

• Make a .env file in the root of the project by duplicating the .env-example file
• Point the paths in .env to those corresponding to your system (OpenWatcom, NASM, DOSBox, etc.)
• Place a copy of your 32-bit DOS extender of choice (dos32a.exe or dos4gw.exe) in the root directory of the project
• Update the DOS_EXTENDER variable in the .env file with your 32-bit DOS extender of choice accordingly (dos32a or dos4gw)
• Run make to build

How To Run

• Run make run to run the built program against the defined DOSBox install
• To run directly in DOSBox, simply mount the build directory and run scroll

mount G /local/path/to/project/build
G:

Minimum System Requirements

• IBM Compatible PC running DOS (MS-DOS, FreeDOS, etc.)
• 32-bit x86 CPU (80386SX 40 MHz or better)
• 4MB RAM
• 16-bit ISA VGA video card (Tseng Labs ET4000AX or better)
• Keyboard

Recommended System Requirements

• 80486DX or Pentium CPU (66 MHz or better)
• 8MB RAM
• VESA Local Bus (VLB) or PCI VGA video card

File Transfer Over Serial

If you have a USB to Serial adapter and Null Modem serial cable, you can use Kermit to easily transfer files between your development machine and your real DOS hardware.

• Ensure your DOS machine is powered down first before trying to connect the Null Modem serial cable to it
• Set up your USB to Serial adapter on your development machine
  • Under Linux, you'll have to add yourself to the group that owns whatever device your adapter maps to before you can use the device as a non-root user
  • NOTE: this procedure may vary depending on your distro

usermod -a -G dialout $USER

• Install Kermit on both your development machine anf your DOS machine
  • Under Linux, you can simply install ckermit via sudo apt-get install ckermit
  • Under DOS, you can download it from here: http://www.columbia.edu/kermit/mskermit.html
• Update the .env file to point to your local serial port and set the transfer speed (bps)

SERIAL_PORT = /dev/ttyUSB0
SERIAL_SPEED = 115200

• Boot into your DOS machine and go into the directory where you want to put your build (e.g. game.exe)
• On your development machine, initiate the file file transfer with make send
• On your DOS machine, run the kermit command to receive the file
  • NOTE: subsequent runs can omit the set speed 115200

kermit set speed 115200, rec game.exe

• Wait for the file to transfer
  • This process should begin immediately, if not you may want to troubleshoot your serial connection or set a lower baud rate on both ends (e.g. 9600bps)

Alternatively, you can also set up DOSBox to use your serial port and kick off the file transfer from there.

serial1=directserial realport:ttyUSB0
kermit set speed 115200, send game.exe

ATTRIBUTIONS

A lot of this code is loosely based on several sources, most derived from Michael Abrash's works featured in Graphics Programming Black Book.

The following projects have been used as references:

• David Brackeen's 256-Color VGA Programming in C (http://www.brackeen.com/vga/)
• @mills32's Little Game Engine for VGA (https://github.com/mills32/Little-Game-Engine-for-VGA)
• @64Mega's Venture-Out! LD44 project (https://github.com/64Mega/ld44-venture-out)
• @root42's Let's Code MS-DOS series (https://github.com/root42/letscode-breakout)

LICENSE

All source code + files outside of the /res folder adheres to the MIT License