TPSWITCH - Routine for switching screens on dual-display systems
----------------------------------------------------------------
TurboPower Software
10/88
Version 1.0
Released to the public domain

Overview
------------------------------------------------------------------------------

Working in conjunction with the TPCRT unit in Turbo Professional 5.0, TPSWITCH
allows you to write programs that write to two different displays (one color,
one monochrome).

The possible uses for TPSWITCH are many. You could use it to write a text
editor that maintains two windows--one on the monochrome display, one on the
color display. You could use it write a program that displays text on the mono
display, graphs on the color display. (With some effort, you could even write
these programs in such a way that dual displays would be used if they are
available, and a single display would be used if they weren't.)

For a simple example of how to use TPSWITCH, see the demonstration program
SWTEST.PAS.

Using TPSWITCH
------------------------------------------------------------------------------

TPSWITCH interfaces the following types, variables, and routines:

type
WhichScreen = (Screen1, Screen2);

This type is used to distinguish between the primary screen (the video
display that was active when the program began) and the secondary screen.
Screen1 represents the primary screen, Screen2 the secondary screen.

const
MonoMode : Word = Mono;
ColorMode : Word = CO80;

These typed constants are used to indicate the mode to switch to the first
time that you switch from Screen1 to Screen2. If the primary screen is a
monochrome display, the first call to SwitchScreens will select the mode
indicated by ColorMode for the secondary screen. If the primary screen is a
color display, the first call will select the mode indicated by MonoMode.

var
CurrentScreen : WhichScreen;

This variable keeps track of the current screen. When the program begins, it
will be initialized to Screen1.

var
HasDualDisplays : Boolean;

This variable, initialized when the program begins, indicates whether dual
displays are present. If it is False, SwitchScreens will do nothing.

procedure SwitchScreens(SC : WhichScreen);
{-Switch from the current screen to the specified screen}

This is the only routine interfaced by TPSWITCH. It should be called each
time you want to switch to a particular screen (Screen1 or Screen2). Note
that SwitchScreens will do nothing if 1) HasDualDisplays is False or 2) SC
is the same as CurrentScreen.

After the screen switch has occurred, the Font8x8Selected routine in TPCRT
will be called to reinitialize most of the state variables used by TPCRT.
Font8x8Selected does not alter WindMin and WindMax (the variables that hold
the current window coordinates), nor does it alter CheckSnow. In fact,
TPSWITCH maintains two sets of window coordinates, one for each screen, and
these coordinates are saved/restored each time you switch screens.