sutherland-hodgman-polygon-clipping.cpp

#include<iostream>
#include<graphics.h>
using namespace std;

int xmin, xmax, ymin, ymax;

class Coordinate{
    public:
    int X;
    int Y;
    Coordinate()    {}
    Coordinate(float x, float y)    {
        X = x;
        Y = y;
    }
};

Coordinate pointOfIntersection(Coordinate s1, Coordinate e1, Coordinate s2, Coordinate e2)
{
    float a1 = e1.Y - s1.Y;
    float b1 = s1.X - e1.X;
    float c1 = a1 * s1.X + b1 * s1.Y;

    float a2 = e2.Y - s2.Y;
    float b2 = s2.X - e2.X;
    float c2 = a2 * s2.X + b2 * s2.Y;

    float delta = a1 * b2 - a2 * b1;

    return Coordinate((b2 * c1 - b1 * c2) / delta, (a1 * c2 - a2 * c1) / delta);
}

int main()
{
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "");

    int i, j, choice=1;
    cout<<"Enter co-ordinates for window ABCD:\n\n";
    cout<<"xmin, xmax, ymin, ymax: ";
    cin>>xmin>>xmax>>ymin>>ymax;
    rectangle(xmin, ymin, xmax, ymax);

    do{
    int n;
    cout<<"\n\nEnter number of vertices (max 10): ";
    cin>>n;
    Coordinate V[n];
    cout<<"Enter co-ordinates of vertices\n";
    int drawPolygon[n*2], newPolygon[100];
    for(i=0, j=0; i<n; i++)  {
        cout<<"Enter x"<<i+1<<" and y"<<i+1<<": ";
        cin>>V[i].X>>V[i].Y;
        drawPolygon[j++] = V[i].X;
        drawPolygon[j++] = V[i].Y;
    }
    drawPolygon[j++] = V[0].X;
    drawPolygon[j] = V[0].Y;
    setcolor(MAGENTA);
    drawpoly(n+1, drawPolygon);

    Coordinate top_left(xmin, ymin), top_right(xmax, ymin), bot_left(xmin, ymax), bot_right(xmax, ymax);
    int newN;

    cout<<endl;
    for(i=0, j=0, newN=0; i<n; i++)  {
        Coordinate temp;
        if(V[i].X<xmin)    {
            if(V[(i+1)%n].X<xmin)
                cout<<"\nOut->Out";
            else    {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_left, bot_left);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nOut->In";
            }
        }
        else    {
            if(V[(i+1)%n].X<xmin)   {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_left, bot_left);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                cout<<"\nIn->Out";
            }
            else    {
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nIn->In";
            }
        }
    }
    newPolygon[j++] = newPolygon[0];
    newPolygon[j] = newPolygon[1];

    setcolor(RED);
    cout<<"\nRed coordinates: ";
    for(i=0; i<=j; i++)
        cout<<newPolygon[i]<<" ";
    drawpoly(newN+1, newPolygon);

    for(i=0, j=0; i<newN; i++) {
        V[i].X = newPolygon[j++];
        V[i].Y = newPolygon[j++];
    }
    n = newN;

    cout<<endl;
    for(i=0, j=0, newN=0; i<n; i++)  {
        Coordinate temp;
        if(V[i].X>xmax)    {
            if(V[(i+1)%n].X>xmax)
                cout<<"\nOut->Out";
            else    {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_right, bot_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nOut->In";
            }
        }
        else    {
            if(V[(i+1)%n].X>xmax)   {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_right, bot_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                cout<<"\nIn->Out";
            }
            else    {
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nIn->In";
            }
        }
    }
    newPolygon[j++] = newPolygon[0];
    newPolygon[j] = newPolygon[1];

    setcolor(GREEN);
    cout<<"\nGreen coordinates: ";
    for(i=0; i<=j; i++)
        cout<<newPolygon[i]<<" ";
    drawpoly(newN+1, newPolygon);

    for(i=0, j=0; i<newN; i++) {
        V[i].X = newPolygon[j++];
        V[i].Y = newPolygon[j++];
    }
    n = newN;

    cout<<endl;
    for(i=0, j=0, newN=0; i<n; i++)  {
        Coordinate temp;
        if(V[i].Y>ymax)    {
            if(V[(i+1)%n].Y>ymax)
                cout<<"\nOut->Out";
            else    {
                temp = pointOfIntersection(V[i], V[(i+1)%n], bot_left, bot_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nOut->In";
            }
        }
        else    {
            if(V[(i+1)%n].Y>ymax)   {
                temp = pointOfIntersection(V[i], V[(i+1)%n], bot_left, bot_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                cout<<"\nIn->Out";
            }
            else    {
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nIn->In";
            }
        }
    }

    newPolygon[j++] = newPolygon[0];
    newPolygon[j] = newPolygon[1];

    setcolor(BLUE);
    cout<<"\nBlue coordinates: ";
    for(i=0; i<=j; i++)
        cout<<newPolygon[i]<<" ";
    drawpoly(newN+1, newPolygon);

    for(i=0, j=0; i<newN; i++) {
        V[i].X = newPolygon[j++];
        V[i].Y = newPolygon[j++];
    }
    n = newN;

    cout<<endl;
    for(i=0, j=0, newN=0; i<n; i++)  {
        Coordinate temp;
        if(V[i].Y<ymin)    {
            if(V[(i+1)%n].Y<ymin)
                cout<<"\nOut->Out";
            else    {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_left, top_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nOut->In";
            }
        }
        else    {
            if(V[(i+1)%n].Y<ymin)   {
                temp = pointOfIntersection(V[i], V[(i+1)%n], top_left, top_right);
                newN++;
                newPolygon[j++] = temp.X;
                newPolygon[j++] = temp.Y;
                cout<<"\nIn->Out";
            }
            else    {
                newN++;
                newPolygon[j++] = V[(i+1)%n].X;
                newPolygon[j++] = V[(i+1)%n].Y;
                cout<<"\nIn->In";
            }
        }
    }

    newPolygon[j++] = newPolygon[0];
    newPolygon[j] = newPolygon[1];

    for(i=0, j=0; i<newN; i++) {
        V[i].X = newPolygon[j++];
        V[i].Y = newPolygon[j++];
    }
    n = newN;

    setcolor(YELLOW);
    drawpoly(newN+1, newPolygon);

    cout<<"\n\nContinue?\t1.Yes\t0.No:\t";
    cin>>choice;
    }while(choice!=0);
    getch();
    closegraph();
}