//-------------------------------------------------------------------
//	shrunken.cpp	         (for Question V on Midterm Exam I)
//
//	Here's a modification of 'shrinker.cpp' giving one possible 
//	solution to Question V on Midterm Exam I as outlined below.
//
//	-----------------------------------------------------------
//
//	This program presently displays the graphics image captured
//	in a file named "captured.img".  Your job is to modify this
//	program so that the displayed image will be reduced in size 
//	from 1024-by-768 to 512-by-384 (i.e., half as wide and half
//	as high as the original screen-image).  You should draw the
//	smaller-sized image so that it is 'centered' on the screen.
//
//	  compile using:  $ g++ shrinker.cpp int86.cpp -o shrinker 
//
//	NOTE: It is unnecessary to download the 'captured.img' file
//	from our class website when you are logged in to one of the
//	computer science department's workstations because the file
//	can be directly accessed via the local network file-system.  
//
//	programmer: ALLAN CRUSE
//	written on: 29 SEP 2005
//-------------------------------------------------------------------

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

int *vram = (int*)0xA0000000; 
int vesa_mode = 0x4123, hres = 1024, vres = 768;
struct vm86plus_struct	vm; 
char imgname[] = "/home/web/cruse/cs686/captured.img"; 

int main( int argc, char **argv )
{
	// memory-map the image-data file into user-space
	int	bmp = open( imgname, O_RDONLY );
	if ( bmp < 0 ) { perror( imgname ); exit(1); }
	int	sz = lseek( bmp, 0, SEEK_END );
	int	*img = (int*)mmap( NULL, sz, PROT_READ, MAP_PRIVATE, bmp, 0 );
	if ( img == MAP_FAILED ) { perror( "mmap" ); exit(1); } 

	// memory-map the video display-memory into user-space
	int	vd = open( "/dev/vram", O_RDWR ); 
	if ( vd < 0 ) { perror( "/dev/vram" ); exit(1); }
	int	size = lseek( vd, 0, SEEK_END ); 
	int	prot = PROT_READ | PROT_WRITE; 
	int	flag = MAP_FIXED | MAP_SHARED; 
	if ( mmap( (void*)vram, size, prot, flag, vd, 0 ) == MAP_FAILED )
		{ perror( "mmap" ); exit(1); } 
	
	// enter graphics mode 
	init8086(); 
	vm.regs.eax = 0x4F02;	
	vm.regs.ebx = vesa_mode;	
	int86( 0x10, vm );	

	// here we transfer this memory-mapped image to the visible screen
	// (so this loop is where all of your code-modifications would go)
	// create a pointer to the reduced image's top-left corner
	int	*dstn = vram + (vres/4)*hres + (hres/4); 
	// loop through one-half the screen's row-numbers
	for (int y = 0; y < vres/2; y++)
		// loop through one-half the screen's column-numbers
		for (int x = 0; x < hres/2; x++)
			{
			// compute RGB color-average for 2-by-2 group 
			int	av_red = 0;	// initialize red sum
			int	av_green = 0;	// initialize green sum	
			int	av_blue = 0;	// initialize blue sum
			// fetch next pixel-group from the image-file
			for (int row = 0; row < 2; row++)
			for (int col = 0; col < 2; col++)
				{
				int	src_index;	
				src_index = (2*y+row)*hres + (2*x+col);
				int	pel = img[ src_index ];
				av_red += (pel>>16)&0xFF;  // add red
				av_green += (pel>>8)&0xFF; // add green
				av_blue += (pel>>0)&0xFF;  // add blue
				}
			av_red /= 4;	// divide red sum by 4
			av_green /= 4;	// divide green sum by 4
			av_blue /= 4;	// divide blue sum by 4
			int 	pel = 0;	// initialize pixel	
			pel |= (av_red<<16);	// merge red average
			pel |= (av_green<<8);	// merge green average
			pel |= (av_blue<<0);	// merge blue average	
			// store this pixel to video display memory
			int	dst_index = y * hres + x;
			dstn[ dst_index ] = pel;
			}

	// wait until the user has finished viewing your displayed image
	getchar();

	// leave graphics mode 
	vm.regs.eax = 0x0003;	
	int86( 0x10, vm );	
	printf( "\n" );
}