VTI Lib

C library (for Z88DK) for VTI graphics board for S100 computers (IMSAI, Altair, Poly88,...). Made for CP/M projects.

VTI (Video Terminal Interface)

VTI is a S100 "graphics" board, made for "Poly88" system, but it works also with other S100 machines like Altair 8800, IMSAI 8080, ...

Here is the board description: http://www.s100computers.com/Hardware%20Folder/PolyMorphic/Video%20Board/Video%20Board.htm

It uses a memory-mapped I/O so writing a single byte to memory would make a character appear on screen. It has a 64x16 chars resolution, and it has a set of "2x3" block characters, so it can reach a 128x48 "pixels" resolution.

Starting address is $F800 by default, but it can be changed using dip-switches. In the IMSAI 8080 in this video it has been changed to $E800 and has some glitches due to a broken RAM chip, which has to be replaced.

Sample code

Here is sort of "hello world":

#include "vti.h"

void main(void) {
  vti_set_start(0xf800); // optional since 0xf800 is the default
  vti_clear_screen();
  
  vti_setmode(VTI_MODE_SET);    // "1" (or VTI_MODE_SET) means "draw"
  vti_line(0, 0, 120, 45);      // segment with coords (0,0)-(120,45).
  
  vti_setmode(VTI_MODE_SET);    // "1" (or VTI_MODE_SET) means "draw"
  vti_boxfill(2, 3, 25, 25);    // box filled with edges (2,3) and (25, 25).
  
  vti_setmode(VTI_MODE_RESET);  // "0" (or VTI_MODE_RESET) means "erase"
  vti_boxfill(3, 4, 25, 25);    // as above, but "0" means "erase"
  
  vti_setmode(VTI_MODE_INVERT); // "2" (or VTI_MODE_INVERT) means "XOR" for each pixel
  vti_boxfill(1, 1, 10, 10);    // box filled with edges (1,1)-(10,10). 
}

Function vti_plot and "mode" parameter

Main function of the library is vti_plot in conjunction with vti_setmode which have the following prototypes:

void vti_setmode(char mode);
void vti_plot(int x, int y);

...where x and y are cartesian coordinates with (0,0) as top-left origin and max values equal to (127,47). The parameter mode represents the way the dot is drawn, and can have the following values:

• 0 = VTI_MODE_RESET. It erases the dot at specified coordinates, making it black.
• 1 = VTI_MODE_SET. It draws the dot, making it white.
• 2 = VTI_MODE_INVERT. It draws the dot if it's currently off (=black), and erases it if it's currently on (=white)

List of library's functions

• vti_set_start(<start address>)
• vti_setmode(<mode>)
• vti_print_at(<x>, <y>, "string")
• vti_clear_screen()
• vti_fill_screen(<char>)
• vti_save_screen(<buffer address>)
• vti_restore_screen(<buffer address>)
• vti_rawchar_at(<x>, <y>, <char>)
• vti_plot(<x>, <y>)
• vti_line(<x0>, <y0>, <x1>, <y1>)
• vti_ellipse_rect(<x0>, <y0>, <x1>, <y1>)
• vti_box(<x0>, <y0>, <x1>, <y1>)
• vti_boxfill(<x0>, <y0>, <x1>, <y1>)
• vti_scroll_up(<number-of-rows>)
• vti_scroll_down(<number-of-rows>)
• vti_put_shape(<x>, <y>, char*, <width>, <height>)
• <pixel> = vti_read_pixel(<x>, <y>)
• <ch> = vti_read_char(<x>, <y>)

Compiling demos

There is a build.bat file which does all the work with Z88DK, this is a sample line:

$ zcc +cpm -clib=8080 demo.c vti.c -o demo.com

Launching demos

By default, the start address is $F800. To use another address, pass it as argument in decimal notation:

$ demo 59392

This will make the demo use $E800 (59392) as start address for the graphics card.

There are the following demos (launch each of them eventually with the start address as parameter):

• ttt.com: tic-tac-toe, inspired by War Games
• demo.com: a bunch of sample of most functions available in the library
• ball.com: a bouncing ball across the screen
• pong.com: the famous game, using a keyboard connected to the VTI's special slot
• bezier.com: drawing of the G-clef, using bezier curves
• fonts.com: draw text with big letters
• lenna.com: drawing of the famous test image https://en.wikipedia.org/wiki/Lenna

Running demo in a video

Credits

Thanks to:

• Alois Zingl for implementation of Bresenham's Algorithms (lines and curves drawing)
• Andrea Matteucci for hardware providing and fixing
• Antonino Porcino for a lot of code optimizazions and demos lenna, fonts
• Brian W. Howell for Tic-Tac-Toe's AI logic
• Andy Glenn for "reverse engineering" of some WarGames screenshots
• Paul Smith for list of WOPR nuclear war scenarios
• George Philips for ASCII-art drawing of USA and USSR resembling WarGames' scene