#include <stdio.h>
#include <stdlib.h>
#include <dos.h>
#include <conio.h>

struct
{
    char    VESASignature[4];       /* 'VESA' 4 byte signature          */
    short   VESAVersion;            /* VBE version number               */
    char    far *OEMStringPtr;      /* Pointer to OEM string            */
    long    Capabilities;           /* Capabilities of video card       */
    unsigned far *VideoModePtr;     /* Pointer to supported modes       */
    short   TotalMemory;            /* Number of 64kb memory blocks     */
    char    reserved[236];          /* Pad to 256 byte block size       */
} VbeInfoBlock;

struct
{
    unsigned short ModeAttributes;      /* Mode attributes                 */
    unsigned char  WinAAttributes;      /* Window A attributes             */
    unsigned char  WinBAttributes;      /* Window B attributes             */
    unsigned short WinGranularity;      /* Window granularity in k         */
    unsigned short WinSize;             /* Window size in k                */
    unsigned short WinASegment;         /* Window A segment                */
    unsigned short WinBSegment;         /* Window B segment                */
    void (far *WinFuncPtr)(void);       /* Pointer to window function      */
    unsigned short BytesPerScanLine;    /* Bytes per scanline              */
    unsigned short XResolution;         /* Horizontal resolution           */
    unsigned short YResolution;         /* Vertical resolution             */
    unsigned char  XCharSize;           /* Character cell width            */
    unsigned char  YCharSize;           /* Character cell height           */
    unsigned char  NumberOfPlanes;      /* Number of memory planes         */
    unsigned char  BitsPerPixel;        /* Bits per pixel                  */
    unsigned char  NumberOfBanks;       /* Number of CGA style banks       */
    unsigned char  MemoryModel;         /* Memory model type               */
    unsigned char  BankSize;            /* Size of CGA style banks         */
    unsigned char  NumberOfImagePages;  /* Number of images pages          */
    unsigned char  res1;                /* Reserved                        */
    unsigned char  RedMaskSize;         /* Size of direct color red mask   */
    unsigned char  RedFieldPosition;    /* Bit posn of lsb of red mask     */
    unsigned char  GreenMaskSize;       /* Size of direct color green mask */
    unsigned char  GreenFieldPosition;  /* Bit posn of lsb of green mask   */
    unsigned char  BlueMaskSize;        /* Size of direct color blue mask  */
    unsigned char  BlueFieldPosition;   /* Bit posn of lsb of blue mask    */
    unsigned char  RsvdMaskSize;        /* Size of direct color res mask   */
    unsigned char  RsvdFieldPosition;   /* Bit posn of lsb of res mask     */
    unsigned char  DirectColorModeInfo; /* Direct color mode attributes    */
    unsigned char  res2[216];           /* Pad to 256 byte block size      */
} ModeInfoBlock;

typedef enum
{
    memPL       = 3,                /* Planar memory model              */
    memPK       = 4,                /* Packed pixel memory model        */
    memRGB      = 6,                /* Direct color RGB memory model    */
    memYUV      = 7,                /* Direct color YUV memory model    */
} memModels;

char mystr[256];
char *get_str();
int     xres,yres;                  /* Resolution of video mode used    */
int     bytesperline;               /* Logical CRT scanline length      */
int     curBank;                    /* Current read/write bank          */
unsigned int bankShift;             /* Bank granularity adjust factor   */
int     oldMode;                    /* Old video mode number            */
char    far *screenPtr;             /* Pointer to start of video memory */
void    (far *bankSwitch)(void);    /* Direct bank switching function   */

int getVbeInfo()
{
    union REGS in,out;
    struct SREGS segs;
    char far *VbeInfo = (char far *)&VbeInfoBlock;
    in.x.ax = 0x4F00;
    in.x.di = FP_OFF(VbeInfo);
    segs.es = FP_SEG(VbeInfo);
    int86x(0x10, &in, &out, &segs);
    return (out.x.ax == 0x4F);
}

int getModeInfo(int mode)
{
    union REGS in,out;
    struct SREGS segs;
    char far *modeInfo = (char far *)&ModeInfoBlock;
    if (mode < 0x100) return 0;     /* Ignore non-VBE modes             */
    in.x.ax = 0x4F01;
    in.x.cx = mode;
    in.x.di = FP_OFF(modeInfo);
    segs.es = FP_SEG(modeInfo);
    int86x(0x10, &in, &out, &segs);
    if (out.x.ax != 0x4F) return 0;
    if ((ModeInfoBlock.ModeAttributes & 0x1)
	    && ModeInfoBlock.MemoryModel == memPK
	    && ModeInfoBlock.BitsPerPixel == 8
	    && ModeInfoBlock.NumberOfPlanes == 1)
	return 1;
    return 0;
}

void setVBEMode(int mode)
{
    union REGS in,out;
    in.x.ax = 0x4F02; in.x.bx = mode;
    int86(0x10,&in,&out);
}

int getVBEMode(void)
{
    union REGS in,out;
    in.x.ax = 0x4F03;
    int86(0x10,&in,&out);
    return out.x.bx;
}

void setBank(int bank)
{
    union REGS  in,out;
    if (bank == curBank) return;    /* Bank is already active           */
    curBank = bank;                 /* Save current bank number         */
    bank <<= bankShift;             /* Adjust to window granularity     */
#ifdef  DIRECT_BANKING
    setbxdx(0,bank);
    bankSwitch();
    setbxdx(1,bank);
    bankSwitch();
#else
    in.x.ax = 0x4F05; in.x.bx = 0;  in.x.dx = bank;
    int86(0x10, &in, &out);
    in.x.ax = 0x4F05; in.x.bx = 1;  in.x.dx = bank;
    int86(0x10, &in, &out);
#endif
}

void putPixel(int x,int y,int color)
{
    long addr = (long)y * bytesperline + x;
    setBank((int)(addr >> 16));
    *(screenPtr + (addr & 0xFFFF)) = (char)color;
}

void line(int x1,int y1,int x2,int y2,int color)
{
    int     d;                      /* Decision variable                */
    int     dx,dy;                  /* Dx and Dy values for the line    */
    int     Eincr,NEincr;           /* Decision variable increments     */
    int     yincr;                  /* Increment for y values           */
    int     t;                      /* Counters etc.                    */
#define ABS(a)   ((a) >= 0 ? (a) : -(a))
    dx = ABS(x2 - x1);
    dy = ABS(y2 - y1);
    if (dy <= dx)
    {
	/* We have a line with a slope between -1 and 1. Ensure that we are
	 * always scan converting the line from left to right to ensure that
	 * we produce the same line from P1 to P0 as the line from P0 to P1. */
	if (x2 < x1)
	{
	    t = x2; x2 = x1; x1 = t;    /* Swap X coordinates           */
	    t = y2; y2 = y1; y1 = t;    /* Swap Y coordinates           */
	}
	if (y2 > y1)
	    yincr = 1;
	else
	    yincr = -1;
	d = 2*dy - dx;              /* Initial decision variable value  */
	Eincr = 2*dy;               /* Increment to move to E pixel     */
	NEincr = 2*(dy - dx);       /* Increment to move to NE pixel    */
	putPixel(x1,y1,color);      /* Draw the first point at (x1,y1)  */
	/* Incrementally determine the positions of the remaining pixels */
	for (x1++; x1 <= x2; x1++)

	{
	    if (d < 0)
		d += Eincr;         /* Choose the Eastern Pixel         */
            else
            {
                d += NEincr;        /* Choose the North Eastern Pixel   */
                y1 += yincr;        /* (or SE pixel for dx/dy < 0!)     */
            }
            putPixel(x1,y1,color);  /* Draw the point                   */
        }
    }
    else
    {
        /* We have a line with a slope between -1 and 1 (ie: includes vertical
         * lines). We must swap x and y coordinates for this. Ensure that we
         * are always scan converting the line from left to right to ensure 
         * that we produce the same line from P1 to P0 as line from P0 to P1.*/
        if (y2 < y1)
        {
            t = x2; x2 = x1; x1 = t;    /* Swap X coordinates           */
            t = y2; y2 = y1; y1 = t;    /* Swap Y coordinates           */
        }
        if (x2 > x1)
            yincr = 1;
        else
            yincr = -1;
        d = 2*dx - dy;              /* Initial decision variable value  */
        Eincr = 2*dx;               /* Increment to move to E pixel     */
        NEincr = 2*(dx - dy);       /* Increment to move to NE pixel    */
        putPixel(x1,y1,color);      /* Draw the first point at (x1,y1)  */
        /* Incrementally determine the positions of the remaining pixels */
        for (y1++; y1 <= y2; y1++)
        {
            if (d < 0)
                d += Eincr;         /* Choose the Eastern Pixel         */
            else
            {
                d += NEincr;        /* Choose the North Eastern Pixel   */
                x1 += yincr;        /* (or SE pixel for dx/dy < 0!)     */
            }
            putPixel(x1,y1,color);  /* Draw the point                   */
        }
    }
}

void drawMoire(void)
{
    int     i;
    for (i = 0; i < xres; i += 5)
    {
        line(xres/2,yres/2,i,0,i % 0xFF);
        line(xres/2,yres/2,i,yres,(i+1) % 0xFF);
    }
    for (i = 0; i < yres; i += 5)
    {
        line(xres/2,yres/2,0,i,(i+2) % 0xFF);
        line(xres/2,yres/2,xres,i,(i+3) % 0xFF);
    }
    line(0,0,xres-1,0,15);
    line(0,0,0,yres-1,15);
    line(xres-1,0,xres-1,yres-1,15);
    line(0,yres-1,xres-1,yres-1,15);
}

char *get_str(char far *p)
{
    int i;
    char *q=mystr;
    for(i=0;i<255;i++)
    {
       if(*p) *q++ = *p++;
       else break;
    }
    *q = '\0';
    return(mystr);
}

void availableModes(void)
{
    unsigned far    *p;
    if (!getVbeInfo())
    {
	printf("No VESA VBE detected\n");
	exit(1);
    }
    printf("VESA VBE Version %d.%d detected (%s)\n\n",
	VbeInfoBlock.VESAVersion >> 8, VbeInfoBlock.VESAVersion & 0xF,
	get_str(VbeInfoBlock.OEMStringPtr));
    printf("Available 256 color video modes:\n");
    for (p = VbeInfoBlock.VideoModePtr; *p !=(unsigned)-1; p++)
    {
	if (getModeInfo(*p))
	{
	    printf("    %4d x %4d %d bits per pixel\n",
		ModeInfoBlock.XResolution, ModeInfoBlock.YResolution,
		ModeInfoBlock.BitsPerPixel);
	}
    }
    printf("\nUsage: hellovbe <xres> <yres>\n");
    exit(1);
}

void initGraphics(unsigned int x, unsigned int y)
{
    unsigned far    *p;
    if (!getVbeInfo())
    {
	printf("No VESA VBE detected\n");
	exit(1);
    }
    for (p = VbeInfoBlock.VideoModePtr; *p != (unsigned)-1; p++)
    {
	if (getModeInfo(*p) && ModeInfoBlock.XResolution == x
		&& ModeInfoBlock.YResolution == y)
	{
	   xres = x;   yres = y;
	   bytesperline = ModeInfoBlock.BytesPerScanLine;
	   bankShift = 0;
	   while ((unsigned)(64 >> bankShift) != ModeInfoBlock.WinGranularity)
	       bankShift++;
	   bankSwitch = ModeInfoBlock.WinFuncPtr;
	   curBank = -1;
	   screenPtr = (char far *)( ((long)0xA000)<<16 | 0);
	   oldMode = getVBEMode();
	   setVBEMode(*p);
	   return;
	}
    }
    printf("Valid video mode not found\n");
    exit(1);
}

void main(int argc,char *argv[])
{
    int x,y;
    if (argc != 3)
	availableModes();       /* Display list of available modes      */
    x = atoi(argv[1]);          /* Get requested resolution             */
    y = atoi(argv[2]);
    initGraphics(x,y);          /* Start requested video mode           */
    drawMoire();                /* Draw a moire pattern                 */
    getch();                    /* Wait for keypress                    */
    setVBEMode(oldMode);        /* Restore previous mode                */
}