//-------------------------------------------------------------------
//	bresdemo.cpp
//
//	This program uses Bresenham's Algorithm to draw some lines.
//
//	  compile using: $ g++ bresdemo.cpp int86.cpp -o bresdemo
//
//	programmer: ALLAN CRUSE
//	written on: 29 SEP 2003
//	revised on: 30 SEP 2005 -- replaced svgalib with 'int86()'
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for lseek() 
#include <sys/mman.h>	// for mman()
#include "int86.h"	// for init8086(), int86()

unsigned char 	*vram = (unsigned char*)0xA0000000;
int 	vesa_mode = 0x4101, hres = 640, vres = 480;
struct vm86plus_struct	vm; 

void exchange( int &x1, int &y1, int &x2, int &y2 )
{
	int	temp;

	temp = x1; 
	x1 = x2; 
	x2 = temp;
	temp = y1; 
	y1 = y2; 
	y2 = temp;
}

void octant_odd( int x1, int y1, int x2, int y2, int color )
{
	// make sure x1 <= x2
	if ( x1 > x2 ) exchange( x1, y1, x2, y2 );
	int	xinc = ( x2 > x1 ) ? 1 : -1;
	int	yinc = ( y2 > y1 ) ? 1 : -1;

	int	dx = (x2-x1)*xinc;
	int	dy = (y2-y1)*yinc;
	int	errorterm = -dx;
	for (int x = x1, y = y1; x <= x2; x++)
		{
		vram[ y*hres + x ] = color;
		errorterm += (dy+dy);
		if ( errorterm >= 0 )
			{
			y += yinc;
			errorterm -= (dx+dx);
			}
		}
}	

void octant_even( int x1, int y1, int x2, int y2, int color )
{
	// make sure y1 <= y2
	if ( y1 > y2 ) exchange( x1, y1, x2, y2 );
	int	xinc = ( x2 > x1 ) ? 1 : -1;
	int	yinc = ( y2 > y1 ) ? 1 : -1;

	int	dx = (x2-x1)*xinc;
	int	dy = (y2-y1)*yinc;
	int	errorterm = -dy;
	for (int x = x1, y = y1; y <= y2; y++)
		{
		vram[ y*hres + x ] = color;
		errorterm += (dx+dx);
		if ( errorterm >= 0 )
			{
			x += xinc;
			errorterm -= (dy+dy);
			}
		}
}

void draw_line( int x1, int y1, int x2, int y2, int color )
{
	int	deltax = ( x1 < x2 ) ? x2-x1 : x1-x2;
	int	deltay = ( y1 < y2 ) ? y2-y1 : y1-y2; 

	if ( deltax > deltay ) octant_odd( x1, y1, x2, y2, color );
	else	octant_even( x1, y1, x2, y2, color );
}


void draw_segments( int x, int y, int xcent, int ycent, int color )
{	
	int	minx = 0, miny = 0, maxx = hres-1, maxy = vres-1;
	int	xlo, xhi, v, h;

	xlo = xcent-x, xhi = xcent+x;
	if ( xlo < minx ) xlo = minx;
	if ( xhi > maxx ) xhi = maxx;
	
	if ( ( v = ycent-y ) >= miny )
		for (h = xlo; h <= xhi; h++) vram[ v*hres + h ] = color;	
	if ( ( v = ycent+y ) <= maxy )
		for (h = xlo; h <= xhi; h++) vram[ v*hres + h ] = color;	
	
	xlo = xcent-y, xhi = xcent+y;
	if ( xlo < minx ) xlo = minx;
	if ( xhi > maxx ) xhi = maxx;
	
	if ( ( v = ycent-x ) >= miny )
		for (h = xlo; h <= xhi; h++) vram[ v*hres + h ] = color;	
	if ( ( v = ycent+x ) <= maxy )
		for (h = xlo; h <= xhi; h++) vram[ v*hres + h ] = color;	
}

void fill_circle( int x, int y, int radius, int color )
{
	int	xcent = x, ycent = y, esum = 3 - 2*radius;
	y = radius, x = 0;
	while ( x <= y )
		{
		draw_segments( x, y, xcent, ycent, color );
		if ( esum < 0 ) { esum += 4*x + 6; ++x; }
		else 	{ esum += 4*(x - y) + 10; y -= 1; ++x; }
		}	
}

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

	do { vram[ y*hres + x ] = color; ++x; } while ( x < maxx );
	do { vram[ y*hres + x ] = color; ++y; } while ( y < maxy );
	do { vram[ y*hres + x ] = color; --x; } while ( x > minx );
	do { vram[ y*hres + x ] = color; --y; } while ( y > miny );
}


int main( int argc, char **argv )
{
	// map display memory into application's address-space
	int	fd = open( "/dev/vram", O_RDWR ); 
	if ( fd < 0 ) { perror( "/dev/vram" ); exit(1); } 
	int	size = lseek( fd, 0, SEEK_END );
	int	prot = PROT_READ | PROT_WRITE; 
	int	flag = MAP_FIXED | MAP_SHARED; 
	if ( mmap( (void*)vram, size, prot, flag, fd, 0 ) == MAP_FAILED )
		{ perror( "mmap" ); exit(1); } 

	// enter graphics mode
	init8086();			// setup 8086 environment
	vm.regs.eax = 0x4F02;		// VESA Set Display Mode
	vm.regs.ebx = vesa_mode;	// specify mode id-number
	int86( 0x10, vm );		// invoke BIOS service

	// draw screen border
	int	color = 15;
	draw_rectangle( 0, 0, hres, vres, color );
	getchar();

	// draw circular disk as background 	
	int	midx = hres/2, midy = vres/2, radius = vres/4;
	color = 5;
	fill_circle( midx, midy, radius, color );
	getchar();

	// draw the first line-pair (yellow)
	color = 14;
	draw_line( 100, 100, hres-100, vres-100, color );
	getchar();
	draw_line( hres-100, 100, 100, vres-100, color );
	getchar();
	
	// draw the second line-pair (cyan)
	color = 11;
	draw_line( 300, 100, hres-300, vres-100, color );
	getchar();
	draw_line( hres-300, 100, 300, vres-100, color );
	getchar();

	// leave graphics mode	
	vm.regs.eax = 0x0003;		// VGA Set Display Mode 3
	int86( 0x10, vm );		// invoke BIOS service
}