/* SCRDEMO.C
*
* Demo about using Timer screen synchronization
*
* Copyright 1994 Petteri Kangaslampi and Jarno Paananen
*
* This file is part of the MIDAS Sound System, and may only be
* used, modified and distributed under the terms of the MIDAS
* Sound System license, LICENSE.TXT. By continuing to use,
* modify or distribute this file you indicate that you have
* read the license and understand and accept it fully.
*/
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <process.h>
#include "midas.h"
signed char horizPan; /* Horizontal Pixel Panning register
value */
ushort startAddr; /* screen start address */
ushort scrSync; /* screen synchronization value */
int panDir; /* panning direction - 0 = left,
1 = right */
/****************************************************************************\
*
* Function: void preVR(void)
*
* Description: Function that is called before Vertical Retrace. Sets the
* new screen start address
*
\****************************************************************************/
void preVR(void)
{
asm {
mov bx,startAddr /* bx = screen start address */
mov dx,03D4h /* CRTC controller */
mov al,0Ch /* Start Address High register */
mov ah,bh /* screen start address high byte */
out dx,ax /* set register value */
mov al,0Dh /* Start Address Low register */
mov ah,bl /* screen start address low byte */
out dx,ax /* set register value */
}
}
/****************************************************************************\
*
* Function: void immVR(void)
*
* Description: Function that is called immediately when Vertical Retrace
* starts. Sets the new Horizontal Pixel Panning value
*
\****************************************************************************/
void immVR(void)
{
asm { mov dx,03DAh /* read Input Status #1 register to */
in al,dx /* reset the Attribute Controller */
/* flip-flop */
mov dx,03C0h /* attribute controller */
mov al,13h + 20h /* Horizontal Pixel Panning register,
enable VGA palette */
out dx,al /* select register */
mov al,horizPan /* Horizontal Pixel Panning value */
out dx,al /* write panning value */
}
}
/****************************************************************************\
*
* Function: void inVR(void)
*
* Description: Function that is called some time during Vertical Retrace.
* Calculates new Horizontal Pixel Panning and screen start
* address values
*
\****************************************************************************/
void inVR(void)
{
/* Note! Although this function does not cause timer synchronization
errors if its execution takes too long, it may still cause errors
to playing tempo when playing with GUS. */
if ( panDir == 0 )
{
/* pan display one pixel left: */
horizPan++; /* next pixel */
if ( horizPan == 9 ) /* is panning 9? */
horizPan = 0; /* if yes, set it to 0 */
if ( horizPan == 8 ) /* is panning 8? */
startAddr++; /* if yes, move to next character */
if ( startAddr == 80 ) /* change direction after */
panDir = 1; /* scrolling one screen */
}
else
{
/* pan display one pixel right: */
horizPan--;
if ( horizPan == -1 ) /* is panning -1? */
horizPan = 8; /* if yes, set it to 8 */
if ( horizPan == 7 ) /* is panning 7? */
startAddr--; /* if yes, move to next character */
if ( (startAddr == 0) && (horizPan == 8) ) /* change direction */
panDir = 0; /* after scrolling back one screen */
}
/* note that charaters are actually 9 pixels wide on VGA */
}
int main(int argc, char *argv[])
{
mpModule *mod;
int error;
/* argv[0] is the program name and argv[1] the module filename, the
rest are options which MIDAS should handle */
/* if there are not enough arguments, show usage and exit: */
if ( argc < 2 )
{
puts("Usage: SCRDEMO <filename> [MIDAS options]");
exit(EXIT_SUCCESS);
}
/* get Timer screen synchronization value: */
if ( (error = tmrGetScrSync(&scrSync)) != OK )
midasError(errorMsg[error]);
midasSetDefaults(); /* set MIDAS defaults */
midasParseEnvironment(); /* parse MIDAS environment string */
midasParseOptions(argc-2, &argv[2]); /* let MIDAS parse all options */
midasInit(); /* initialize MIDAS Sound System */
mod = midasPlayModule(argv[1], 0); /* load module and start playing */
puts("Playing - type \"EXIT\" to stop.");
horizPan = 8;
startAddr = 0;
panDir = 0;
/* Synchronize Timer to screen. preVR() will be called before
Vertical Retrace, immVR() just after Vertical Retrace starts and
inVR() some time later during Vertical Retrace. */
if ( (error = tmrSyncScr(scrSync, &preVR, &immVR, &inVR)) != OK )
midasError(errorMsg[error]);
/* jump to DOS shell: */
spawnl(P_WAIT, getenv("COMSPEC"), NULL);
/* stop timer screen synchronization: */
tmrStopScrSync();
/* reset panning and start address: (dirty but works) */
horizPan = 8;
startAddr = 0;
preVR();
immVR();
midasStopModule(mod); /* stop playing */
midasClose(); /* uninitialize MIDAS */
return 0;
}
