//-------------------------------------------------------------------
//	cgademo.cpp
//
//	This program demonstrates early IBM-PC graphics programming
//	with 32KB of installed video memory (real address 0xB8000),
//	supporting either 2-colors or 4-colors using "packed-pixel"
//	memory organization, using two separate 16KB display pages. 
//	(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() 

typedef unsigned char	u8;

u8	*vram = (u8*)0x000B8000;
int	hres, vres;
void	(*set_pixel)( int x, int y, int color );

void set_pixel_1( int x, int y, int color )
{
	int	posn = 0x2000*(y % 2) + 80*(y / 2) + (x / 8);
	int	mask = 0x80 >> (x % 8);
	u8	temp = vram[ posn ];

	color &= 1;
	color <<= 7;
	color >>= (x % 8);

	temp &= ~mask;
	temp |= color;
			
	vram[ posn ] = temp;
}

void set_pixel_2( int x, int y, int color )
{
	int	posn = 0x2000*(y % 2) + 80*(y / 2) + ((2 * x) / 8);
	int	mask = 0xC0 >> ((2 * x) % 8);
	u8	temp = vram[ posn ];

	color &= 3;
	color <<= 6;
	color >>= ((2 * x) % 8);

	temp &= ~mask;
	temp |= color; 	
			
	vram[ posn ] = temp;
}

void map_vram( int base, int size );

int main( int argc, char **argv )
{
	int	base = (int)vram;
	int	size = (32 << 10);
	map_vram( base, size );

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

	//---------------------------------------------
	// Demonstrate CGA color graphics (VGA mode 5)
	//---------------------------------------------
	system( "clear ; mode3 5 " );	// 320x200, 4-colors
	hres = 320, vres = 200, set_pixel = set_pixel_2;
	
	// draw screen border
	color = 3;	// 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();

	// fill circle (unrescaled)
	midx = hres/2; midy = vres/2; 
	radius_squared = 60*60;
	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;
		color = ( dist_squared < radius_squared ) ? 1 : 2;
		set_pixel( x, y, color );
		}	
	getchar();

	// fill circle (adjusted)
	radius_squared *= 30;
	for (y = 4; y <= maxy-4; y++) 
	for (x = 4; x <= maxx-4; x++)
		{
		int	dx = (x - midx)*5;
		int	dy = (y - midy)*6;
		int	dist_squared = dx*dx + dy*dy;
		color = ( dist_squared < radius_squared ) ? 1 : 2;
		set_pixel( x, y, color );
		}	
	getchar();

	//--------------------------------------------------
	// Demonstrate CGA monochrome graphics (VGA mode 6)
	//--------------------------------------------------
	system( "clear ; mode3 6 " );	// 640x200, 2-colors
	hres = 640, vres = 200, set_pixel = set_pixel_1;
	
	// draw screen border
	minx = 0, maxx = hres-1;
	miny = 0, maxy = vres-1;
	x = y = 0; 	color = 1; // white
	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();

	// fill circle (unrescaled)
	midx = hres/2; midy = vres/2; radius_squared = 60*60;
	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;
		color = ( dist_squared < radius_squared ) ? 1 : 0;
		set_pixel( x, y, color );
		}	
	getchar();

	// fill circle (adjusted)
	radius_squared *= 60;
	for (y = 4; y <= maxy-4; y++) for (x = 4; x <= maxx-4; x++)
		{
		int	dx = (x - midx)*5;
		int	dy = (y - midy)*12;
		int	dist_squared = dx*dx + dy*dy;
		color = ( dist_squared < radius_squared ) ? 1 : 0;
		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 );
}