//-------------------------------------------------------------------
//	vgademo.cpp
//
//	This example demonstrates 256-color PC graphics programming
//	as implemented by IBM's Video Graphics Array (VGA) adapter, 
//	still supported by SVGA devices for backward compatibility.
//	Screen-resolution is 320-by-200, and pixel-depth is 8-bits.
//	This mode uses the DAC's 256 color-lookup registers, but it
//	disregards the Attribute Controller's 16 palette registers.
//
//	  compile using:  $ g++ vgademo.cpp int86.cpp -o vgademo
//
//	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_VGA  0x000A0000

typedef unsigned char	u8;

u8 *vram = (u8*)VRAM_BASE_FOR_VGA;
struct vm86plus_struct	vm;
int hres = 320, vres = 200;


void set_pixel( int x, int y, int color )
{
	int	posn = y*hres + x;

	vram[ posn ] = color;
}	

	
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 );
}


int main( int argc, char **argv )
{
	int	minx, midx, maxx, miny, midy, maxy;
	int	x, y, color, radius_squared;

	printf( "\e[H\n" );		// avoids getchar jerk
	init8086();			// enable BIOS service

	//--------------------------------------------------
	// Demonstrate VGA 256-color graphics (IBM mode 19)
	//--------------------------------------------------
	vm.regs.eax = 0x0013;		// Set Display Mode 19
	int86( 0x10, vm );		// invoke BIOS service

	// draw a 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();

	// fill circle (unrescaled)
	midx = hres/2; midy = 23*vres/32; 
	radius_squared = 40*40; 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;
		color = ( dist_squared < radius_squared ) ? 6 : 150;
		set_pixel( x, y, color );
		}	
	getchar();

	// show the palette of 256-colors
	int	h = 5, v = 5, x0 = 32, y0 = 24;
	for (color = 0; color < 256; color++)
		{
		x = x0 + (color % 32)*8;
		y = y0 + (color / 32)*8;
		fill_rectangle( x, y, h, v, color );
		}	
	getchar();

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