//-------------------------------------------------------------------
//	horizpan.cpp
//	
//	This program illustrates some effects of reprogramming the
//	display pitch, by writing a new value into the CRTC Offset
//	Register (port 0x3D4, index 0x13).  (The CRT Start Address
//	is then incremented, or decremented, to perform horizontal
//	panning over an enlarged logical screensize which is twice
//	as wide as the actual physical screensize.)
//
//	programmer: ALLAN CRUSE
//	written on: 26 NOV 2003
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <termios.h>	// for tcgetattr(), tcsetattr() 
#include <sys/mman.h>	// for mmap() 
#include <sys/io.h>	// for iopl() 

#define VRAM_BASE_ADDRESS 0xA0000000 
#define VGA_MEMORY_LENGTH ( 4 << 20) 

unsigned char *vram = (unsigned char*)VRAM_BASE_ADDRESS; 
const int display_mode = 0x4101, hres = 640, vres = 480; 


int pitch = 640;


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


int map_system_memory( int base, int size ) 
{
	int	fd = open( "/dev/vram", O_RDWR ); 
	if ( fd < 0 ) { perror( "/dev/vram" ); return -1; } 
	int	prot = PROT_READ | PROT_WRITE; 
	int	flag = MAP_FIXED | MAP_SHARED; 
	void	*mm = (void*)base; 
	if ( mmap( mm, size, prot, flag, fd, 0 ) == MAP_FAILED ) 
		{ perror( "mmap" ); return -1; } 
	close( fd ); 
}


int main( int argc, char **argv )
{
	// setup i/o permissions and map video frame-buffer
	if ( iopl( 3 ) ) { perror( "iopl" ); exit(1); }
	system( "/sbin/insmod vram.o" ); 
	map_system_memory( VRAM_BASE_ADDRESS, VGA_MEMORY_LENGTH ); 

	// reprogram the terminal for non-canonical input
	struct termios	otty; 
	tcgetattr( 0, &otty ); 
	struct termios	tty = otty; 
	tty.c_lflag &= ~( ICANON | ECHO | ISIG ); 
	tty.c_cc[ VMIN ] = 1; 
	tty.c_cc[ VTIME ] = 0; 
	tcsetattr( 0, TCSAFLUSH, &tty ); 

	// enter graphics mode
	char	command[ 40 ]; 
	sprintf( command, " clear ; mode3 %d ", display_mode ); 
	system( command ); 

	// draw a white border (640x480)
	int	color = 15; 
	draw_rectangle( 0, 0, hres, vres, color ); 
	getchar(); 

	// color horizontal scanlines alternately green and red
	for (int v = 1; v < vres-1; v++)
		{
		color = ( v % 2 ) ? 2 : 4;
		for (int h = 1; h < hres-1; h++) 
			vram[ v*hres + h ] = color;
		}
	getchar();
	
	// reprogram the CRTC Offset Register (for 1280x480)
	outb( 0x13, 0x3D4 );
	int	orig_offset = inw( 0x3D4 );
	int	work_offset = orig_offset;
	work_offset += (orig_offset & ~0xFF);
	outw( work_offset, 0x3D4 );
	getchar();

	// perform horizontal panning by incrementing CRTC Start Address
	int	start = 0;
	for (int i = 0; i < 160; i++)
		{
		++start;
		outw( ((start << 8)&0xFF00)|0x0D, 0x3D4 );
		outw( ((start << 0)&0xFF00)|0x0C, 0x3D4 );
		getchar();
		}
	getchar();

	// modify our software 'display_pitch' variable
	pitch *= 2;

	// draw a yellow border for our new 'logical' screensize
	int	wide = hres *2;
	int	high = vres;	
	color = 14;
	draw_rectangle( 0, 0, wide, high, color );
	getchar();

	// draw concentric rectangles to fill the new screensize
	color = 32;
	for (int i = 1; i < vres/2; i++)
		{
		wide -= 2;
		high -= 2;
		draw_rectangle( i, i, wide, high, color );
		++color;
		}
	getchar();

	// perform horizontal panning by decrementing CRTC Start Address
	for (int i = 0; i < 160; i++)
		{
		--start;
		outw( ((start << 8)&0xFF00)|0x0D, 0x3D4 );
		outw( ((start << 0)&0xFF00)|0x0C, 0x3D4 );
		getchar();
		}
	getchar();

	// leave graphics mode
	system( " mode3 3 " ); 
	tcsetattr( 0, TCSAFLUSH, &otty ); 
}