//-------------------------------------------------------------------
//	setreset.cpp
//
//	This program demonstrates the operation of the VGA Graphics
//	Controller's SET/RESET and ENABLE SET/RESET registers while
//	the video display mode is setup for 16 simultaneous colors;
//	default values are used for Write Mode and Function Select.
//
//	  compile using: $ g++ setreset.cpp int86.cpp -o setreset
//
//	programmer: ALLAN CRUSE
//	written on: 04 SEP 2005
//-------------------------------------------------------------------

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

#define VRAM_BASE_FOR_VGA  0x000A0000
#define GRFX_INDEX_PORT		0x3CE

typedef unsigned char u8;

u8 *vram = (u8*)VRAM_BASE_FOR_VGA;
struct vm86plus_struct	vm;
int vga_mode = 18, hres = 640, vres = 480;

u8 glyph[ ] = {	0xFF, 0xFF, 0xFF,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xC0, 0x00, 0x03,
		0xFF, 0xFF, 0xFF };


void draw_glyph( int row, int col, int reg0, int reg1 )
{
	u8	*dst = vram + row * 640 + col;

	outw( (reg0<<8) | 0, GRFX_INDEX_PORT );	// Set/Reset
	outw( (reg1<<8) | 1, GRFX_INDEX_PORT );	// Enable Set/Reset

	for (int i = 0; i < 48; i++) 
		dst[ (i / 3) * 80 + (i % 3) ] = glyph[ i ];
}


void write_string( int row, int col, int color, char *msg )
{
	// restore default-values to Graphics Controller registers
	outw( 0x0000, GRFX_INDEX_PORT );	// Set/Reset
	outw( 0x0001, GRFX_INDEX_PORT );	// Enable Set/Reset

	// copy string to conventional memory and determine length	
	char	*mem = (char*)0x00018000;
	int	length = 0;
	while ( mem[ length ] = msg[ length ] ) ++length;
	
	// invoke the Video ROM-BIOS 'write_string' service  
	vm.regs.ecx = length;
	vm.regs.ebx = color & 0xF;
	vm.regs.edx = (row << 8) | (col & 0xFF);
	vm.regs.ebp = 0;
	vm.regs.es  = ((int)mem >> 4);
	vm.regs.eax = 0x1300;
	int86( 0x10, vm );
}


int main( int argc, char **argv )
{
	// setup the display for 16-color graphics (640-by-480)
	printf( "\e[H\n" );		// avoids getchar jerk
	init8086();			// allows I/O and BIOS	
	vm.regs.eax = vga_mode;		// Set Display Mode 18
	int86( 0x10, vm );		// invoke BIOS service

	// draw our glyph using every possible combination of values 
	// for Set/Reset (by rows) and Enable Set/Reset (by columns)
	for (int reg0 = 0; reg0 < 16; reg0++)
		for (int reg1 = 0; reg1 < 16; reg1++)
			draw_glyph( 3*(reg0+3), 4*(reg1+3), reg0, reg1 );

	// draw the title and explanatory legend
	write_string(  1, 27, 15, "A Study of VGA Write Mode 0" );
	write_string(  3,  0,  7, "Enable Set/Reset \032" );
	write_string(  4,  0,  7, "Set/Reset \031" );
	getchar();			// awaits <RETURN>-key

	// restore the display to standard 80-by-25 text-mode
	vm.regs.eax = 0x0003;		// Set Display Mode 3
	int86( 0x10, vm );		// invoke BIOS service
}