clip.cpp

#include <iostream>
using namespace std;

// Defining region codes
const int INSIDE = 0; // 0000
const int LEFT = 1; // 0001
const int RIGHT = 2; // 0010
const int BOTTOM = 4; // 0100
const int TOP = 8; // 1000

// Defining x_max, y_max and x_min, y_min for
// clipping rectangle. Since diagonal points are
// enough to define a rectangle
const int x_max = 10;
const int y_max = 8;
const int x_min = 4;
const int y_min = 4;

// Function to compute region code for a point(x, y)
int computeCode(double x, double y)
{
	// initialized as being inside
	int code = INSIDE;

	if (x < x_min) // to the left of rectangle
		code |= LEFT;
	else if (x > x_max) // to the right of rectangle
		code |= RIGHT;
	if (y < y_min) // below the rectangle
		code |= BOTTOM;
	else if (y > y_max) // above the rectangle
		code |= TOP;

	return code;
}

// Implementing Cohen-Sutherland algorithm
// Clipping a line from P1 = (x2, y2) to P2 = (x2, y2)
void cohenSutherlandClip(double x1, double y1,
						double x2, double y2)
{
	// Compute region codes for P1, P2
	int code1 = computeCode(x1, y1);
	int code2 = computeCode(x2, y2);

	// Initialize line as outside the rectangular window
	bool accept = false;

	while (true) {
		if ((code1 == 0) && (code2 == 0)) {
			// If both endpoints lie within rectangle
			accept = true;
			break;
		}
		else if (code1 & code2) {
			// If both endpoints are outside rectangle,
			// in same region
			break;
		}
		else {
			// Some segment of line lies within the
			// rectangle
			int code_out;
			double x, y;

			// At least one endpoint is outside the
			// rectangle, pick it.
			if (code1 != 0)
				code_out = code1;
			else
				code_out = code2;

			// Find intersection point;
			// using formulas y = y1 + slope * (x - x1),
			// x = x1 + (1 / slope) * (y - y1)
			if (code_out & TOP) {
				// point is above the clip rectangle
				x = x1 + (x2 - x1) * (y_max - y1) / (y2 - y1);
				y = y_max;
			}
			else if (code_out & BOTTOM) {
				// point is below the rectangle
				x = x1 + (x2 - x1) * (y_min - y1) / (y2 - y1);
				y = y_min;
			}
			else if (code_out & RIGHT) {
				// point is to the right of rectangle
				y = y1 + (y2 - y1) * (x_max - x1) / (x2 - x1);
				x = x_max;
			}
			else if (code_out & LEFT) {
				// point is to the left of rectangle
				y = y1 + (y2 - y1) * (x_min - x1) / (x2 - x1);
				x = x_min;
			}

			// Now intersection point x, y is found
			// We replace point outside rectangle
			// by intersection point
			if (code_out == code1) {
				x1 = x;
				y1 = y;
				code1 = computeCode(x1, y1);
			}
			else {
				x2 = x;
				y2 = y;
				code2 = computeCode(x2, y2);
			}
		}
	}
	if (accept) {
		cout << "Line accepted from " << x1 << ", "
			<< y1 << " to " << x2 << ", " << y2 << endl;
		// Here the user can add code to display the rectangle
		// along with the accepted (portion of) lines
	}
	else
		cout << "Line rejected" << endl;
}

// Driver code
int main()
{
	// First Line segment
	// P11 = (5, 5), P12 = (7, 7)
	cohenSutherlandClip(5, 5, 7, 7);

	// Second Line segment
	// P21 = (7, 9), P22 = (11, 4)
	cohenSutherlandClip(7, 9, 11, 4);

	// Third Line segment
	// P31 = (1, 5), P32 = (4, 1)
	cohenSutherlandClip(1, 5, 4, 1);

	return 0;
}