//-------------------------------------------------------------------
//	drawtext.cpp
//
//	This program shows how a graphics application can draw text,
//	based on a character glyph-table stored in the VGA firmware.   
//	We can draw the text against an existing colored pattern and
//	we can put our text at an arbitrary pixel-location onscreen.
//	
//	  compile using:  $ g++ drawtext.cpp int86.cpp -o drawtext
//		 
//	programmer: ALLAN CRUSE
//	written on: 05 SEP 2005
//-------------------------------------------------------------------

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

#define VRAM_BASE_ADDRESS 0x000A0000
#define GC_PORT		  0x03CE

unsigned char *vram = (unsigned char*)VRAM_BASE_ADDRESS;
struct vm86plus_struct	vm;
int vga_mode = 18, hres = 640, vres = 480;
char pattern[] = { 0x00, 0x00, 0x33, 0x33, 0x00, 0x00, 0x33, 0x33 };

void draw_character( int x, int y, int color, char *glyph )
{
	int	which = y * hres + x;
	int	where = which / 8;
	int	shift = which % 8;
	int	mask = 0xFF >> shift;

	// Here we use VGA Write Mode 3 ("Masked Write") 	
	outw( 0x0305, GC_PORT );		// Write Mode 3
	outw( (color<<8) | 0, GC_PORT );	// Set/Reset 
	outw( (shift<<8) | 3, GC_PORT );	// Data-Rotate register
	
	// pass one draws the glyph's left-hand portion
	outw( (mask<<8) | 8, GC_PORT );	// left-hand Bit Mask 
	for (int row = 0; row < 16; row++)
		{
		int	temp = vram[ where + 80*row ];	// load latches
		vram[ where + 80*row ] = glyph[ row ]; 	// draw fgcolor
		}
	++where;	// the byte-address following the starting cell  
	if (( shift == 0 )||( (where % 80) == 0 )) return;

	// pass two draws the glyph's right-hand portion
	outw( (~mask<<8) | 8, GC_PORT );	// right-hand Bit Mask 
	for (int row = 0; row < 16; row++)
		{
		int	temp = vram[ where + 80*row ];	// load latches
		vram[ where + 80*row ] = glyph[ row ]; 	// draw fgcolor
		}
}

void put_pixel( int x, int y, int color )
{
	int	which = y * hres + x;
	int	where = which / 8;
	int	shift = which % 8;
	int	mask = 0x80 >> shift;
	
	outw( (mask<<8) | 8, GC_PORT );		// Bit Mask
	outw( (color<<8) | 0, GC_PORT );	// Set/Reset
	outw( 0x0F01, GC_PORT );		// Enable Set/Reset 
	vram[ where ] = vram[ where ];		// "Direct Write"
}

void bios_write_string( int row, int col, int color, char *msg )
{
	// restore defaults to GC registers
	outw( 0x0000, GC_PORT );	// Set/Reset
	outw( 0x0001, GC_PORT );	// Enable Set/Reset
	outw( 0x0003, GC_PORT );	// Data-Rotate/Function-Select
	outw( 0x0005, GC_PORT );	// Write Mode 0 ("Direct Write")
	outw( 0xFF08, GC_PORT );	// Bit Mask

	// copy string to real-mode memory (and determine length)
	char	*src = (char*)0x18000;
	int	length = 0;
	while ( src[ length ] = msg[ length ] ) ++length;
	
	// setup register-parameters and invoke int-0x10, function 0x13
	vm.regs.ecx = length;
	vm.regs.es  = ((int)src >> 4);
	vm.regs.ebp = 0;
	vm.regs.ebx = (color & 0xFF);
	vm.regs.edx = (row << 8) | (col & 0xFF);
	vm.regs.eax = 0x1300;
	int86( 0x10, vm );
}


int main( int argc, char **argv )
{
	// initialize environment for executing ROM-BIOS services
	init8086();

	// now locate the 8x16 character-glyph table in firmware
	vm.regs.eax = 0x1130;	// Get Font Information
	vm.regs.ebx = 0x0600;	// address of 8x16 font 
	int86( 0x10, vm );	// invoke BIOS service 
	char	*font = (char*)(vm.regs.es * 16L + vm.regs.ebp);
	printf( "\e[H\e[J\nAddress of 8x16 font: %08X \n", (int)font );
	getchar();
	
	// enter graphics mode (640-by480, 16-colors) 
	vm.regs.eax = vga_mode;		// Set Display Mode 18
	int86( 0x10, vm );		// invoke BIOS service

	// draw a white screen border
	int	xmin = 0, xmax = hres-1, ymin = 0, ymax = vres-1;
	int	x = 0, y = 0, color = 15;
	do { put_pixel( x, y, color ); ++x; } while ( x < xmax );	
	do { put_pixel( x, y, color ); ++y; } while ( y < ymax );	
	do { put_pixel( x, y, color ); --x; } while ( x > xmin );	
	do { put_pixel( x, y, color ); --y; } while ( y > ymin );	
	getchar();
	
	// tile part of the bordered area with a two-color pattern
	xmin = 1, ymin = 8, xmax = 79, ymax = 470;
	int	fg = 9;		// foreground color is normal blue
	int	bg = 1;		// background color is bright blue
	outw( (bg<<8) | 0, GC_PORT );
	outw( (fg<<8) | 1, GC_PORT );
	outw( 0x0005, GC_PORT );  // Write Mode 0 ("Direct Write")
	outw( 0xFF08, GC_PORT );  // Bit Mask enables all pixels
	outw( 0x0003, GC_PORT );  // Data-Rotation/Function-Select
	for (y = ymin; y < ymax; y++) 
		for (x = xmin; x < xmax; x++)
			vram[ y * 80 + x ] = pattern[ y % 8 ];
	getchar();			
			
	// draw a text message using the BIOS 'WriteString' function  
	char	message[] = " Hello, world! ";
	int	row = 4, col = 34, green = 0x0A;  // bright green
	bios_write_string( row, col, green, message );
	getchar();

	// draw some text messages against our patterned background 
	int	len = sizeof( message ) - 1;
	color = green;
	do	{
		++row;
		y = row * 36;
		x = (col * 8) + color;
		for (int i = 0; i < len; i++)
			{
			char	*cp = font + 16*message[i];
			draw_character( x, y, color, cp );
			x += 8;
			} 
		getchar();
		}
	while ( ++color < 16 );

	// restore text mode
	vm.regs.eax = 0x0003;
	int86( 0x10, vm );
	printf( "End of \'drawtext\' demo \n" );
}