/*	____________________

	clipping
	
	This program illustrates the Cohen
	Sutherland clipping algorithm using
	sample C code.

*/

/*	____________________

	includes, defines, types, prototypes
	
*/

#include <stdio.h>

#define TRUE 1
#define FALSE 0
typedef struct       /* a rectangle in world coordinates */
{
	double  top, left, bottom, right;
} windRect ;

int code(double x, double y);
int clip(double *x1, double *y1, double *x2, double *y2);
void setWindow(double top, double left, double bottom, double right);
void setScale(void);

windRect _window;               /* the window */
double _windowCenterx, _windowCentery;

/*      ______________________________________________________________

	setWindow

	This function sets a global variable, named
	_window.  _window is a rectangle of type windRect.

*/

void setWindow(double top, double left, double bottom, double right)

{
	_window.top = top;
	_window.left = left;
	_window.bottom = bottom;
	_window.right = right;
	_windowCenterx = (_window.left + _window.right) / 2.0;
	_windowCentery = (_window.top + _window.bottom) / 2.0;
/*	setScale();*/

}       /* End of setWindow */


/*	____________________

	main
	
	This program ...
	
	Arguments:
		argc	argument count
		argv	array of pointers to arguments
	
	Returns:
	
	Side Effects:
	
	Problems:

*/

main(int argc, char *argv)

{
	double x, y, x1, y1;
	setWindow(0.0, 0.0, 100.0, 100.0);
	
	x = 50.0;
	y = 50.0;
	x1 = 150.0;
	y1 = 50.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = -50.0;
	y = 50.0;
	x1 = 150.0;
	y1 = 50.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 50.0;
	y1 = 50.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 140.0;
	y1 = 0.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 50.0;
	y1 = 50.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 50.0;
	x1 = 60.0;
	y1 = 60.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 50.0;
	y1 = 50.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 50.0;
	y1 = -150.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

	x = 50.0;
	y = 150.0;
	x1 = 160.0;
	y1 = 60.0;
	
	printf("x=%lf y=%lf x1=%lf y1=%lf\n", x, y, x1, y1);
	if(clip(&x, &y, &x1, &y1))
		printf("x=%lf y=%lf x1=%lf y1=%lf\n\n", x, y, x1, y1);

}	/* End of main */

/*	____________________

	code
	
	This function computes the 4 bit
	patterns which classify points as
	to which of the 9 regions of the
	plane they reside.
	
	Arguments:
		x	a double
		y	a double
	
	Returns:	an int containing the
				4 bit pattern
	
	Side Effects:	none
	
	Problems:	none

*/

int code(double x, double y)

{
	return	(x < _window.left) << 3 |
			(x > _window.right) << 2 |
			(y < _window.top) << 1 |
			(y > _window.bottom);

}	/* End of code */

/*	____________________

	clip
	
	This function implements the Cohen
	Sutherland clipping algorithm
	
	Arguments:
		x1		pointer to a double
		y1		pointer to a double
		x2		pointer to a double
		y2		pointer to a double
	
	Returns:	the clipped values
	
	Side Effects:	changes its arguments
	
	Problems:	none

*/

int clip(double *x1, double *y1, double *x2, double *y2)

{
	int c1 = code(*x1, *y1),
		c2 = code(*x2, *y2);
	double dx, dy;
	
	while(c1 | c2)
	{
		if(c1 & c2)
			return FALSE;
		dx = *x2 - *x1;
		dy = *y2 - *y1;
		if(c1)
		{
			if(c1 & 8)
			{
				*y1 += dy * (_window.left-*x1)/dx; *x1 = _window.left;
			}
			else if(c1 & 4)
			{
				*y1 += dy * (_window.right-*x1)/dx; *x1 = _window.right;
			}
			else if(c1 & 2)
			{
				*x1 += dx * (_window.top-*y1)/dy; *y1 = _window.top;
			}
			else if(c1 & 1)
			{
				*x1 += dx * (_window.bottom-*y1)/dy; *y1 = _window.bottom;
			}
			c1 = code(*x1, *y1);
		}
		else
		{
			if(c2 & 8)
			{
				*y2 += dy * (_window.left-*x2)/dx; *x2 = _window.left;
			}
			else if(c2 & 4)
			{
				*y2 += dy * (_window.right-*x2)/dx; *x2 = _window.right;
			}
			else if(c2 & 2)
			{
				*x2 += dx * (_window.top-*y2)/dy; *y2 = _window.top;
			}
			else if(c2 & 1)
			{
				*x2 += dx * (_window.bottom-*y2)/dy; *y2 = _window.bottom;
			}
			c2 = code(*x2, *y2);
		}
	}
	return TRUE;
	
}	/* End of clip */