Selecting a video display mode

To ensure a common denominator, the LCAU programs have been written for PC and PC-clone type microcomputers with a CGA video controller. They will work without further alteration on all the compatible video controllers, such as EGA and VGA, of course with neither increased resolution nor additional colors.

A complication arises while working with cellular automata of half-integral radius, which means to say, those whose neighborhoods are of even length. To align the new generation with the old, it should be shifted by half a cell width. With a given (low) resolution there is no alternative to shifting the line, but with higher resolution, two consecutive pixels can be alloted to each cell. Shifting is accomplished by changing the parity of the assignment.

The representation of automata with five or more states likewise presents a problem, given that CGA can only show four colors, including black. Using larger pixels with composite colors reduces the number of cells in a video display which does not bear close scrutiny.

A video controller which goes under the trade name of PLANTRONICS offers doubled resolution with sixteen colors, amongst its other options. In most of the LCAU series, provision has been made for the PLANTRONICS mode. Options in the main menu provide for switching modes.

For binary automata, where additional colors are not needed, and where monochromatic pixels can still be split by going to higher resolution, a different selection of options exists, yielding different color schemes.

As yet, no reconciliation has been made between the PLANTRONICS mode and either EGA or VGA. PLANTRONICS mode is implemented by setting a flag at the same time that the mode assignment is loaded into the output port of the controller, which is the only element of hardware involved. The TURBO C functions PEEK and POKE are used to deposit information in the video memory area when the PLANTRONICS mode is active.



Harold V. McIntosh
E-mail:mcintosh@servidor.unam.mx