//-------------------------------------------------------------------
//	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.)
//
//	programmer: ALLAN CRUSE
//	written on: 07 SEP 2003
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for close() 
#include <sys/mman.h>	// for mman() 
#include <sys/io.h>	// for iopl()

typedef unsigned char	u8;

u8	*vram = (u8*)0x000A0000;
int	hres = 640, vres = 350;

void set_pixel( int x, int y, int color )
{
	int	posn = y*80 + (x / 8);
	int	mask = 0x80 >> (x % 8);

	// Using the Graphics Controller's Write Mode 0 ("Direct Write")
	
	// 1.  Load fill-color into Set/Reset register (index 0)
	outw( (color << 8)|0, 0x3CE );
	
	// 2.  Load 0x0F into Enable Set/Reset register (index 1)
	outw( 0x0F01, 0x3CE );

	// 3.  Setup Data-Rotate/Function-Select register (index 3)
	outw( 0x0003, 0x3CE );

	// 4.  Program the controller's Bit Mask register (index 8)
	outw( (mask << 8)|8, 0x3CE );
	
	// 5.  Load the latches, then write to vram	
	vram[ posn ] = vram[ posn ];
}

void fill_rectangle( int x, int y, int h, int v, int color )
{
	int	minx = x, maxx = x+h-1;
	int	miny = y, maxy = y+v-1;

	for (y = miny; y <= maxy; y++)
		for (x = minx; x <= maxx; x++)
			set_pixel( x, y, color );
}


void map_vram( int base, int size );

int main( int argc, char **argv )
{
	int	base = (int)vram;
	int	size = (256<<10);
	map_vram( base, size );

	int	minx, midx, maxx, miny, midy, maxy;
	int	x, y, color, radius_squared;

	//----------------------------------------------
	// Demonstrate EGA color graphics (VGA mode 16)
	//----------------------------------------------
	system( "clear ; mode3 16 " );	// 640x350, 16-colors

	// draw screen border
	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();

	system( " mode3 3 " );	// standard 80x25 text mode
}


void map_vram( int base, int size )
{
	int	fd = open( "/dev/mem", O_RDWR );
	if ( fd < 0 ) { perror( "/dev/mem" ); exit(1); }
	int	prot = PROT_READ | PROT_WRITE;
	int	flag = MAP_FIXED | MAP_SHARED;
	void	*mm = (void*)base;
	if ( mmap( mm, size, prot, flag, fd, base ) == MAP_FAILED )
		{ perror( "mmap" ); exit(1); }
	close( fd );
}