Xref:	news2.mv.net comp.os.msdos.djgpp:4804
From:	fwk AT pacific DOT net DOT sg (Foo Wan Kin)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Help on SVGA 640X480X256
Date:	Mon, 10 Jun 1996 10:33:23 GMT
Organization:	Pacific Internet, Singapore
Lines:	117
Message-ID:	<4ph17q$cqo@raffles.technet.sg>
NNTP-Posting-Host:	max85ppp39.pacific.net.sg
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi all,

	I have encountered some problems when I try to experiment with
VESA video mode 0x101 (640 X 480 X 256 colours). I tried to map the
linear video memory and fill all the 640 X 480 bytes with a single
color. However, it seems there are some 'holes' on the screen that are
not filled. I have used the grx 2.0 graphics library to do the same
thing but the problem does not show up.

	Can anyone help me on this? Below is the codes.

TIA,
Wan Kin

-- begin codes --
#include <stdio.h>
#include <stdlib.h>
#include <dpmi.h>
#include <go32.h>
#include <dos.h>

#define FnGetVBEModeInfo        0x4F01
#define FnSetVBEMode            0x4F02

#define MODE80X25TEXT           0x0003
#define MODE640X480X256         0x101

#define LINEAR_FRAME_BUFFER     0x80
#define LINEAR_BIT_ENABLE       0x4000

// VBE Mode Information Block Structure
typedef struct VBEModeInfoBlock
{
  short ModeAttributes          __attribute__ ((packed));
  char  WinAAttributes          __attribute__ ((packed));
  char  WinBAttributes          __attribute__ ((packed));
  short WinGranularity          __attribute__ ((packed));
  short WinSize                 __attribute__ ((packed));
  short WinASegment             __attribute__ ((packed));
  short WinBSegment             __attribute__ ((packed));
  int   WinFuncPtr              __attribute__ ((packed));
  short BytesPerScanLine        __attribute__ ((packed));
  short XResolution             __attribute__ ((packed));
  short YResolution             __attribute__ ((packed));
  char  XCharSize               __attribute__ ((packed));
  char  YCharSize               __attribute__ ((packed));
  char  NumberOfPlanes          __attribute__ ((packed));
  char  BitsPerPixel            __attribute__ ((packed));
  char  NumberOfBanks           __attribute__ ((packed));
  char  MemoryModel             __attribute__ ((packed));
  char  BankSize                __attribute__ ((packed));
  char  NumberOfImagePages      __attribute__ ((packed));
  char  PageReserved            __attribute__ ((packed));
  char  Blank[9]                __attribute__ ((packed));
  int   PhysBasePtr             __attribute__ ((packed));
  int   OffScreenMemOffset      __attribute__ ((packed));
  short OffScreenMemSize        __attribute__ ((packed));
  char  Reserved[206]           __attribute__ ((packed));
} VBEModeInfo;


int main()
{
 VBEModeInfo modeinfo;
 __dpmi_regs r;
 __dpmi_meminfo meminfo;
 int video_address,video_ds,pixel;

 // Get mode 0x101 info
 r.x.ax = FnGetVBEModeInfo;
 r.x.cx = MODE640X480X256;
 r.x.es = __tb / 16;
 r.x.di = 0;
 __dpmi_int(0x10, &r);
 
 if (!r.h.ah)
 { 
  dosmemget(__tb,sizeof(VBEModeInfo),&modeinfo);

  if (modeinfo.ModeAttributes&LINEAR_FRAME_BUFFER) 
  {
   meminfo.size = modeinfo.XResolution*modeinfo.YResolution;
   meminfo.address = modeinfo.PhysBasePtr;
    
   if (__dpmi_physical_address_mapping(&meminfo) != -1)
   {
    // Set video to mode 0x101
    video_address = meminfo.address;
    r.x.ax = FnSetVBEMode;
    r.x.bx = MODE640X480X256|LINEAR_BIT_ENABLE;
    __dpmi_int(0x10,&r);
    
    if ( r.h.al == 0x4F && !r.h.ah) 
    {
     //Assign a selector to video memory
     video_ds = __dpmi_allocate_ldt_descriptors(1);
     __dpmi_set_segment_base_address(video_ds,video_address);
     video_address = 0;
     __dpmi_set_segment_limit(video_ds,
      (modeinfo.XResolution*modeinfo.YResolution)|0xFFF);
   
     for (pixel=0;pixel<modeinfo.XResolution*modeinfo.YResolution;
          pixel++) 
      _farpokeb(video_ds,pixel,7);

     getch();

     r.x.ax = MODE80X25TEXT;
     __dpmi_int(0x10,&r);
    }
   }
  }
 }
}

-- end codes --

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