5.cohen-sutherland.cpp

/* Program: Clip a lines using Cohen-Sutherland algorithm */

#include <GL/glut.h>
#include <stdio.h>
#define outcode int

double xmin = 50, ymin = 50, xmax = 100, ymax = 100;
double xvmin = 200, yvmin = 200, xvmax = 300, yvmax = 300;

float X0, Y0, X1, Y1;
const int RIGHT = 2;
const int LEFT = 1;
const int TOP = 8;
const int BOTTOM = 4;

outcode ComputeOutCode(double x, double y);

void CohenSutherlandLineClipAndDraw(double x0, double y0, double x1, double y1)
{
	outcode outcode0, outcode1, outcodeOut;
	bool accept = false, done = false;
	outcode0 = ComputeOutCode(x0, y0);
	outcode1 = ComputeOutCode(x1, y1);

	do {
		if (!(outcode0 | outcode1)) {
			accept = true;
			done = true;
		} else if (outcode0 & outcode1)
			done = true;
		else {
			double x, y, m;
			m = (y1 - y0) / (x1 - x0);
			outcodeOut = outcode0 ? outcode0 : outcode1;
			if (outcodeOut & TOP) {
				x = x0 + (ymax - y0) / m;
				y = ymax;
			} else if (outcodeOut & BOTTOM) {
				x = x0 + (ymin - y0) / m;
				y = ymin;
			} else if (outcodeOut & RIGHT) {
				y = y0 + (xmax - x0) * m;
				x = xmax;
			} else {
				y = y0 + (xmin - x0) * m;
				x = xmin;
			}
			if (outcodeOut == outcode0) {
				x0 = x;
				y0 = y;
				outcode0 = ComputeOutCode(x0, y0);
			} else {
				x1 = x;
				y1 = y;
				outcode1 = ComputeOutCode(x1, y1);
			}
		}
	} while (!done);
	glColor3f(1.0, 0.0, 0.0);
	glBegin(GL_LINE_LOOP);
	glVertex2f(xvmin, yvmin);
	glVertex2f(xvmax, yvmin);
	glVertex2f(xvmax, yvmax);
	glVertex2f(xvmin, yvmax);
	glEnd();
	printf("\n%f   %f :  %f   %f", x0, y0, x1, y1);

	if (accept) {
		double sx = (xvmax - xvmin) / (xmax - xmin);
		double sy = (yvmax - yvmin) / (ymax - ymin);
		double vx0 = xvmin + (x0 - xmin) * sx;
		double vy0 = yvmin + (y0 - ymin) * sy;
		double vx1 = xvmin + (x1 - xmin) * sx;
		double vy1 = yvmin + (y1 - ymin) * sy;

		glColor3f(0.0, 0.0, 1.0);
		glBegin(GL_LINES);
		glVertex2d(vx0, vy0);
		glVertex2d(vx1, vy1);
		glEnd();
	}
}

outcode ComputeOutCode(double x, double y)
{
	outcode code = 0;
	if (y > ymax)
		code |= TOP;
	else if (y < ymin)
		code |= BOTTOM;
	if (x > xmax)
		code |= RIGHT;
	else if (x < xmin)
		code |= LEFT;
	return code;
}
void display()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0, 0.0, 0.0);
	glBegin(GL_LINES);
	glVertex2d(X0, Y0);
	glVertex2d(X1, Y1);
	glEnd();
	glColor3f(0.0, 0.0, 1.0);
	glBegin(GL_LINE_LOOP);
	glVertex2f(xmin, ymin);
	glVertex2f(xmax, ymin);
	glVertex2f(xmax, ymax);
	glVertex2f(xmin, ymax);
	glEnd();
	CohenSutherlandLineClipAndDraw(X0, Y0, X1, Y1);
	glFlush();
}

void myinit()
{
	glClearColor(1.0, 1.0, 1.0, 1.0);
	glColor3f(1.0, 0.0, 0.0);
	glPointSize(1.0);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0.0, 499.0, 0.0, 499.0);
}

void main(int argc, char** argv)
{
	printf("Enter end points : ");
	scanf("%f%f%f%f", &X0, &Y0, &X1, &Y1);
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowSize(500, 500);
	glutInitWindowPosition(0, 0);
	glutCreateWindow("Cohen Sutherland Line Clipping    
			Algorithm");
	glutDisplayFunc(display);
	myinit();
	glutMainLoop();
}