/*  VGAINI.C */

#include "dos.h"
#include "memory.h"

/* Port addresses of control regs */
#define GRAPHICS 0x3ce

/* Registers within controllers */
#define GRSETRESET 0
#define GRENABLESETRESET 1
#define GRROTATE 3
#define GRCONTROL 5
#define GRBITMASK 8

/* the funcion select modes */
#define FS_DIRECT 0
#define FS_AND 0x10
#define FS_OR 0x20
#define FS_XOR 0x30

typedef unsigned char BYTE;
static BYTE far *graphicsbase = MK_FP(0xa000,0);

/* Subroutine to write to a VGA controller port */
static void WriteVGA(int port, BYTE reg, BYTE value)
{
	outportb(port,reg);
	outportb(port+1,value);
}
/* Put us in text mode */
void TextMode(void)
{
	asm mov ax,3;
	asm int 0x10;
}
/* Put us in Graphics mode */
void GraphMode(void)
{
	asm mov ax,0x12;
	asm int 0x10;
}
/* Draw a pixel on the screen */
void DrawPixel(int x, int y, BYTE color)
{
  int offset=y*80 + x/8;
	int mask=0x80>>(x&7);
	int temp;

	/* set color */
	WriteVGA(GRAPHICS,GRSETRESET,color);			/* color = our color */
	WriteVGA(GRAPHICS,GRENABLESETRESET,15);

	/* select bit mask to modify */
	WriteVGA(GRAPHICS,GRBITMASK,mask);

	/* latch current data, this reads all four planes into internal latches */
	temp = graphicsbase[offset];

	/* write the bit by mixing the latched data with the bitmask and color regs*/
	graphicsbase[offset] = 0xff;
	

	/* now reset things so the BIOS can function */
	WriteVGA(GRAPHICS,GRBITMASK,0xff);
	WriteVGA(GRAPHICS,GRENABLESETRESET,0);
}
/* Clear the screen to a given color */
void ClearScreen(int color)
{
	int i,j;
	for (i=0; i < 640; i++)
		for (j=0; j < 480; j++)
			DrawPixel(i,j,color);
}
void main(void)
{
	unsigned i,j;
	GraphMode();
	
	ClearScreen(1);

	for (i= 0; i < 400; i++) {
		DrawPixel(i,39,14);
		DrawPixel(i,40,14);
	}
	while (!kbhit());
	getch();
	TextMode();
}