computer graphics description & program

Now that we know how to initialise the mouse, display the mouse pointer, hide it if required, get the current position of the mouse cursor and status of the mouse buttons we can put all this to use to do something worthwhile. Drawing rectangles using mouse, for example. I have written this program for a VGA mono monitor in 640 x 480 resolution graphics mode. But it works even on other monitors with lower resolutions without making any changes.

              #include "graphics.h"  
#include "dos.h"  
#include "alloc.h"
union REGS i, o ;  
int  midx, midy ;  
char far *p1, far *p2, far *p3, far *p4 ;
main( )  
{  
int gd = DETECT, gm, button, x, y, sx, sy, tx, ty, x1, y1, x2, y2 ;
if ( initmouse( ) == 0 )  
{  
printf ( "\nMouse driver not loaded..." ) ;    
exit ( 1 ) ;  
}
  

  initgraph ( &gd, &gm, "c:\\tc\\bgi" ) ;  
gotoxy ( 1, 1 )  ;    
printf ( "Draw box....." ) ;  
gotoxy ( 60, 1 ) ;    
printf ( "Right button to exit" ) ;
do  
{  
showmouseptr( ) ;    
getmousepos ( &button, &tx, &ty ) ;
if ( button & 1 == 1 )  
{  
hidemouseptr( ) ;  
sx = x = x1 = x2 = tx ;    
sy = y = y1 = y2 = ty ;  
setcolor ( WHITE ) ;  
save ( x1, y1, x2, y2 ) ;  
rectangle ( x1, y1, x2, y2 ) ;  
getmousepos ( &button, &tx, &ty ) ;

while ( ( button & 1 ) == 1 )  
{     
if ( x != tx || y != ty )  
{  
setcolor ( BLACK ) ;    
rectangle ( x1, y1, x2, y2 ) ;  
restore ( x1, y1 ) ;    
x = tx ;    
y = ty ;
if ( x <sx )  
{  
x1 = x ;    
x2 = sx ;  
}  
else  
{  
x1 = sx ;    
x2 = x ;  
}
if ( y <sy )  
{  
y1 = y ;    
y2 = sy ;  
}  
else  
{  
y1 = sy ;   
y2 = y ;  
}
setcolor ( WHITE ) ;    
save ( x1, y1, x2, y2 ) ;  
rectangle ( x1, y1, x2, y2 ) ;  
}
getmousepos ( &button, &tx, &ty ) ;  
}
restore ( x1, y1 ) ;    
showmouseptr( ) ;  
}  
} while ( ( button & 2 ) != 2 ) ;
gotoxy ( 1, 1 )  ;    
printf ( "Press any key to exit" ) ;  
gotoxy ( 60, 1 ) ;    
printf ( " " ) ;  
getch( ) ;    
closegraph( ) ;  
}
save ( int x1, int y1, int x2, int y2 )  
{  
unsigned area1, area2, area3, area4 ;
midx = x1 + (x2 - x1) / 2 ;    
midy = y1 + (y2 - y1) / 2 ;
area1 = imagesize ( x1, y1, midx, midy ) ;  
p1 = farmalloc ( area1 ) ;  
area2 = imagesize ( midx + 1, y1, x2, midy ) ;  
p2 = farmalloc ( area2 ) ;  
area3 = imagesize ( x1, midy + 1, midx, y2 ) ;  
p3 = farmalloc ( area3 ) ;  
area4 = imagesize ( midx + 1, midy + 1, x2, y2 ) ;  
p4 = farmalloc ( area4 ) ;
if ( p1 == NULL || p2 == NULL || p3 == NULL || p4 == NULL )  
{  
closegraph( ) ;  
printf ( "Memory allocation error!" ) ;   
exit ( 2 ) ;  
}
getimage ( x1, y1, midx, midy, p1 ) ;  
getimage ( midx + 1, y1, x2, midy, p2 ) ;  
getimage ( x1, midy + 1, midx, y2, p3 ) ;  
getimage ( midx + 1, midy + 1, x2, y2, p4 ) ;  
}
restore ( int x1, int y1 )  
{  
putimage ( x1, y1, p1, OR_PUT ) ;  
putimage ( midx + 1, y1, p2, OR_PUT ) ;  
putimage ( x1, midy + 1, p3, OR_PUT ) ;  
putimage ( midx + 1, midy + 1, p4, OR_PUT ) ;
farfree ( p1 ) ;    
farfree ( p2 ) ;  
farfree ( p3 ) ;   
farfree ( p4 ) ;  
}
initmouse( )    
{  
i.x.ax = 0 ;  
int86 ( 0x33, &i, &o ) ;  
return ( o.x.ax ) ;  
}
showmouseptr( )    
{  
i.x.ax = 1 ;  
int86 ( 0x33, &i, &o ) ;  
}
hidemouseptr( )    
{  
i.x.ax = 2 ;  
int86 ( 0x33, &i, &o ) ;  
}
restrictmouseptr ( int x1, int y1, int x2, int y2 )   
{  
i.x.ax = 7 ;    
i.x.cx = x1 ;    
i.x.dx = x2 ;  
int86 ( 0x33, &i, &o ) ;  
i.x.ax = 8 ;    
i.x.cx = y1 ;    
i.x.dx = y2 ;  
int86 ( 0x33, &i, &o ) ;  
} 
getmousepos ( int *button, int *x, int *y )  
{  
i.x.ax = 3 ;  
int86 ( 0x33, &i, &o ) ;  
*button = o.x.bx ;    
*x = o.x.cx ;    
*y = o.x.dx ;  
}