//-------------------------------------------------------------------
//	egademo.cpp
//
//	This program demonstrates "enhanced" PC graphics programming
//	with 256KB of installed video memory (real address 0xA0000),
//	supporting 16-colors using four overlapping memory "planes".
//	(Supported by VGA/SVGA devices for backward compatibility.)
//
//	  compile using:  $ g++ egademo.cpp int86.cpp -o egademo
//
//	programmer: ALLAN CRUSE
//	written on: 01 SEP 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf()  
#include <sys/io.h>	// for inb(), outw(), etc.
#include "int86.h"	// for init8086(), int86()

#define VRAM_BASE_FOR_EGA 0x000A0000
#define GFXC_INDEX_PORT	      0x03CE

typedef unsigned char	u8;

u8 *vram = (u8*)VRAM_BASE_FOR_EGA;
struct vm86plus_struct	vm;

void set_pixel( int x, int y, int color )
{
	// Using the Graphics Controller's Write Mode 0 ("Direct Write")
	int	posn = y*80 + (x / 8);
	int	mask = 0x80 >> (x % 8);
	
	// 1.  Load fill-color into Set/Reset register (index 0)
	outw( (color << 8)|0, GFXC_INDEX_PORT );
	
	// 2.  Load 0x0F into Enable Set/Reset register (index 1)
	outw( 0x0F01, GFXC_INDEX_PORT );

	// 3.  Setup Data-Rotate/Function-Select register (index 3)
	outw( 0x0003, GFXC_INDEX_PORT );

	// 4.  Program the controller's Bit Mask register (index 8)
	outw( (mask << 8)|8, GFXC_INDEX_PORT );
	
	// 5.  Load the latches from vram, then write back to vram	
	vram[ posn ] = vram[ posn ];
}

void fill_rectangle( int x, int y, int h, int v, int color )
{
	int	xmin = x, xmax = x+h-1, ymin = y, ymax = y+v-1;

	for (y = ymin; y <= ymax; y++)
		for (x = xmin; x <= xmax; x++)
			set_pixel( x, y, color );
}

int main( int argc, char **argv )
{
	int	hres, vres, minx, midx, maxx, miny, midy, maxy;
	int	x, y, color, radius_squared;
	
	printf( "\e[H\n" );		// avoids getchar jerk
	init8086();			// enable BIOS service
	//----------------------------------------------
	// Demonstrate EGA color graphics (IBM mode 16)
	//----------------------------------------------
	vm.regs.eax = 0x0010;		// Set Display Mode 16
	int86( 0x10, vm );		// invoke BIOS service

	// draw screen border
	hres = 640, vres = 350, color = 15; // white
	minx = 0, maxx = hres-1;
	miny = 0, maxy = vres-1;
	x = y = 0;
	do { set_pixel( x, y, color ); ++x; } while ( x < maxx );
	do { set_pixel( x, y, color ); ++y; } while ( y < maxy );
	do { set_pixel( x, y, color ); --x; } while ( x > minx );
	do { set_pixel( x, y, color ); --y; } while ( y > miny );
	getchar();

	// show the palette of 16-colors
	int	h = 40, v = 40, x0 = 64, y0 = 48;
	for (color = 0; color < 16; color++)
		{
		x = x0 + (color % 8)*64;
		y = y0 + (color / 8)*64;
		fill_rectangle( x, y, h, v, color );
		}	
	getchar();
	
	// fill circle (unrescaled)
	midx = hres/2; midy = 23*vres/32; 
	radius_squared = 80*80; color = 6;
	for (y = 4; y <= maxy-4; y++) 
	for (x = 4; x <= maxx-4; x++)
		{
		int	dx = x - midx;
		int	dy = y - midy;
		int	dist_squared = dx*dx + dy*dy;
		if ( dist_squared < radius_squared ) 
			set_pixel( x, y, color );
		}	
	getchar();

	// return the display to standard text mode
	vm.regs.eax = 0x0003;		// Set Display Mode 3
	int86( 0x10, vm );		// invoke BIOS service
	printf( "EGA demo is finished\n" );
}