Cohen Line clipping algorithm

 

// C++ program to implement Cohen Sutherland algorithm

// for line clipping.

#include <iostream>

#include <GL/glut.h>

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 = 100;

const int y_max = 100;

const int x_min = 40;

const int y_min = 40;

int x1,x2,y1,y2;

// 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;

}

}

if (accept)

{

cout <<"Line accepted from (" << x1 << ", "

<< y1 << " to "<< x2 << ", " << y2 << ") because its completely VISIBLE" << endl;

// Here the user can add code to display the rectangle

// along with the accepted (portion of) lines

}

else

        cout <<"Line rejected from (" << x1 << ", "

<< y1 << " to "<< x2 << ", " << y2 << ") because its completely INVISIBLE" << endl;

}

 void display()

 {

        glClear(GL_COLOR_BUFFER_BIT);

        glColor3f(0.0,1.0,0.0);

        glBegin(GL_LINES);

        glVertex2i(40,100);

        glVertex2i(40,10);

        glVertex2i(100,100);

        glVertex2i(100,10);

        glVertex2i(40,100);

        glVertex2i(100,100);

        glVertex2i(40,10);

        glVertex2i(100,10);

        glColor3f(1.0,0.0,0.0);

        //Visible line

        glVertex2i(50,60);

        glVertex2i(70,40);

        //Invisible line

        glVertex2i(150,100);

        glVertex2i(180,50);

        glEnd();

        glFlush();

 }

 void myInit(void)

        {

            glClearColor(0.0,0.0,0.0,1.0);

            glPointSize(2.0);

            glMatrixMode(GL_PROJECTION);

            glLoadIdentity();

            gluOrtho2D(0,200,0,200);

        }

// Driver code

int main(int argc, char**argv)

{

    cout<<" The coordinates of the clipping window are (40,100), (100,100), (100,10) and (40,40)"<<endl;

    // First Line segment

// P11 = (5, 5), P12 = (7, 7) completely VISIBLE(inside)

cohenSutherlandClip(50, 60, 70, 40);

// P11 = (5, 5), P12 = (7, 7) completely INVISIBLE(outside)

cohenSutherlandClip(150, 100, 180, 150);

    glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

// giving window size in X- and Y- direction

glutInitWindowSize(400,400);

glutInitWindowPosition(0,0);

// Giving name to window

    glutCreateWindow("Cohen-Sutherland line clipping algorithm");

    myInit();

glutDisplayFunc(display);

glutMainLoop();

return 0;

}

output: