Programming With VESA BIOS Extensions

Listing 1: VBE wrapper functions

#include <string.h>
#include <dos.h>
#include "vbe.h"    /* exports and data types */

/*------------------ local data -------------------*/

static VbeInfo_t _VbeInfo;  
static ModeInfo_t _ModeInfo;

static int _Width;   /* scan line width in bytes */
static long _Window; /* memory window size in bytes */
static int _Segment; /* mem window segment */

/*--------------- exported functions ---------------*/

int VbeGetVbeInfo(VbeInfo_t far *p)

/* fetches the vbe info block; returns 0 if no vbe. */
{
    union REGS r={0x4f00,0,0,0,0,FP_OFF(p)};
    struct SREGS s={FP_SEG(p)};

    if(!p) return 0;
        
    _fmemset(p,0,sizeof(VbeInfo_t));
    _fmemcpy(p->VbeSignature,"VBE2",4);
    int86x(0x10,&r,&r,&s);

    if(_fmemcmp(p->VbeSignature,"VESA",4)) return 0;
    return r.x.ax==0x4f;
}
int VbeGetModeInfo(int mode,ModeInfo_t far *p)

/* fetches the mode info block for the specified mode 
   number; returns 0 if mode unsupported by vbe. */
{
    union REGS r={0x4f01,0,mode,0,0,FP_OFF(p)};
    struct SREGS s={FP_SEG(p)};

    if(!p) return 0;
    
    _fmemset(p,0,sizeof(ModeInfo_t));
    int86x(0x10,&r,&r,&s);

    return r.x.ax==0x4f;
}
int VbeSetMode(int mode)

/* initializes the requested video mode; returns 0 if 
   there's no vbe or the mode is unavailable. */
{
    union REGS r={0x4f02,mode};

    if(!VbeGetVbeInfo(&_VbeInfo)) return 0;
    
    if(mode>=0x100)    /* svga mode */
    {
        if(!VbeGetModeInfo(mode,&_ModeInfo) || 
            !(_ModeInfo.ModeAttributes&1)) return 0;
    
        _Width=_ModeInfo.BytesPerScanLine;
        _Window=1024L*_ModeInfo.WinSize;    /* convert to bytes */
        _Segment=_ModeInfo.WinASegment;        
    }
    int86(0x10,&r,&r);
    
    return r.x.ax==0x4f;
}
void VbeSetPalette(const char far *p,int start,int n)

/* loads the dac palette registers; uses bios on vbe
   versions before 2.0 */
{
    if(_VbeInfo.VbeVersion<0x200)    /* use bios */
    {
        union REGS r={0x1012,start,n,FP_OFF(p)};
        struct SREGS s={FP_SEG(p)};
        int86x(0x10,&r,&r,&s);
    }
    else    /* use vbe */
    {
        union REGS r={0x4f09,0,n,start,0,FP_OFF(p)};
        struct SREGS s={FP_SEG(p)};
        int86x(0x10,&r,&r,&s);
    }
}
void VbeSetWindow(int window,int position)

/* repositions the indicates memory window to the new
   position (in WinGranularity units). */
{
    union REGS r={0x4f05,window,0,position};
    int86(0x10,&r,&r);
}
void VbeWrite(int x,int y,int bytes,const char far *buffer)

    /* copies the contents of the buffer (<64k) to display, 
    starting at pixel (x,y). */

{
    long absolute=x+(long)y*_Width;      /* absolute offset */
    long position=absolute/_Window;      /* of window */
    long offset=absolute%_Window;        /* of window */
    char far *vram=MK_FP(_Segment,0);    /* to window */

    VbeSetWindow(0,(int)position);
    
    if(offset+bytes>_Window)    /* data overruns window */
    {
        int    n=(int)(_Window-offset);  /* bytes left */
        
        _fmemcpy(vram+offset,buffer,n);  /* display 1st part */
        VbeSetWindow(0,(int)++position); /* move window */
        _fmemcpy(vram,buffer+n,bytes-n); /* display rest */
    }    
    else _fmemcpy(vram+offset,buffer,bytes);/* no overrun */
}
/* End of File */