/* vesa.c */
#define VESA
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dos.h>
#include "vidlib.h"
#include "vesa.h"

int   VESAmode(unsigned int mode, char *palette)
{
    _AX=0x4f02;
    _BX=mode;
    geninterrupt(0x10);
    if ( _AH == 0 ) {
       if (palette != NULL)          /* if not NULL */
          if (palette == DEFAULTDAC) /* restore defaults */
             WriteDACs(_olddacs);
          else
             WriteDACs(palette);
       getVESAinfo(mode);
       _screen_start=(char far *)0xA0000000L;
       _screen_width=Vminfo.bytesperline;
       VESAsetpage(0);
       return(1);
    } else
       return(0);
}

int    isVESA(void)
{
    union   REGS    regs;
    struct  SREGS   sregs;

    regs.x.ax = 0x4F00;             /* VESA BIOS call               */
    sregs.es = FP_SEG(&Vinfo);      /* Place address into parm list */
    regs.x.di= FP_OFF(&Vinfo);
    int86x(0x10, &regs, &regs, &sregs);     /* Try VESA BIOS        */
					/* Check status and signature   */
    if ((regs.x.ax != 0x004F) ||
        (strncmp(Vinfo.signature,"VESA",4) != 0) ) {
	return(0);
    }
    return(1);
}

/* returns 1 for a valid mode, 0 if not */
int    isVESAmode(int mode)
{
     struct REGS r;
     struct SREGS s;

     r.h.ah=0x4f; r.h.al=0;
     s.es=FP_SEG(&Vinfo);
     r.x.di=FP_OFF(&Vinfo);
     int86x(0x10,&r,&r,&s);
     if (r.x.ax != 0x004f) {
           return(0);
     }
     if (strncmp(Vinfo.signature,"VESA",4) == 0) {
          while ((*(Vinfo.modeptr) != 0xFFFF) &&
                 (*(Vinfo.modeptr) != mode) )
                  Vinfo.modeptr++;
          if (*Vinfo.modeptr == mode) {
             return(1);
          } else {
             return(0);
          }
     }  else {
          return(0);
     }
}

struct vesainfo *getVESAinfo(int mode)
{
    struct REGS r;
    struct SREGS s;

    r.h.ah=0x4f; r.h.al=0x01; r.x.cx=mode;
    s.es=FP_SEG(&Vminfo); r.x.di=FP_OFF(&Vminfo);
    int86x(0x10,&r,&r,&s);
    if ( r.x.ax == 0x004F ) {
       return(&Vinfo);
    }  else {
       return(NULL);
    }
}

int VESAsetpage(unsigned page) /* assume window 0 */
{
   _AH=0x4F;
   _AL=5;
   _BH=0;
   _BL=0;
   _DX=page;
   geninterrupt(0x10);
   if (_AH == 0) {
      vesapage=page;
      VESAnext_break();
      return(page);
   } else {
      return(0);
   }
}

int  VESAsetpagew(char window, unsigned page)
{
   _BH=0; _BL=window; _DX=page;
   (*Vminfo.Windowsetptr)();
   vesapage=page;
   VESAnext_break();
   return(1);
}

int VESAsetpagewbios(char window, unsigned page)
{
   struct REGS r;

   r.h.ah=0x4f; r.h.al=5;
   r.h.bh=0;    r.h.bl=window;
   r.x.dx=page;
   int86(0x10,&r,&r);
   vesapage=page;
   VESAnext_break();
   return(!r.h.ah);
}

void   VESAnext_break(void)
{
   long ao, ws;
   ws=(long)Vminfo.size<<10;
   ao=(long)(vesapage * ws + ws); /* = first byte of next page */
   Vnext_break=(unsigned int)(ao/(long)Vminfo.bytesperline);
   Vnext_break_offset=(unsigned int)((ao-1L) % Vminfo.bytesperline);
}

int VESAfirst_page(int scan, int offset)
{
   long ao, ws;
   ws=(long)Vminfo.size<<10;
   ao=( (long)scan * (long)Vminfo.bytesperline) + offset;
   return((int)(ao/ws));
}