Monday 1 February 2016

Fill a Polygon Using Scan Line Fill Algorithm in C++

// Program to Fill a Polygon Using Scan Line Fill Algorithm in C++.
#include <conio.h>
#include <iostream>
#include <graphics.h>
#include <stdlib.h>
using namespace std;

//Declaration of class point
class point
{
    public:
    int x,y;
};

class poly
{
    private:
        point p[20];
        int inter[20],x,y;
        int v,xmin,ymin,xmax,ymax;
    public:
        int c;
        void read();
        void calcs();
        void display();
        void ints(float);
        void sort(int);
};


void poly::read()
{
    int i;
    cout<<"\n\t SCAN_FILL ALGORITHM";
    cout<<"\n Enter the no of vertices of polygon:";
    cin>>v;
    if(v>2)
    {
        for(i=0;i<v; i++) //ACCEPT THE VERTICES
        {
            cout<<"\nEnter the co-ordinate no.- "<<i+1<<" : ";
            cout<<"\n\tx"<<(i+1)<<"=";
            cin>>p[i].x;
            cout<<"\n\ty"<<(i+1)<<"=";
            cin>>p[i].y;
        }
        p[i].x=p[0].x;
        p[i].y=p[0].y;
        xmin=xmax=p[0].x;
        ymin=ymax=p[0].y;
    }
    else
        cout<<"\n Enter valid no. of vertices.";
}
//FUNCTION FOR FINDING
void poly::calcs()
{ //MAX,MIN
    for(int i=0;i<v;i++)
    {
        if(xmin>p[i].x)
        xmin=p[i].x;
        if(xmax<p[i].x)
        xmax=p[i].x;
        if(ymin>p[i].y)
        ymin=p[i].y;
        if(ymax<p[i].y)
        ymax=p[i].y;
    }
}
//DISPLAY FUNCTION
void poly::display()
{
    int ch1;
    char ch='y';
    float s,s2;
    do
    {
        cout<<"\n\nMENU:";
        cout<<"\n\n\t1 . Scan line Fill ";
        cout<<"\n\n\t2 . Exit ";
        cout<<"\n\nEnter your choice:";
        cin>>ch1;
        switch(ch1)
        {
            case 1:
                s=ymin+0.01;
                delay(100);
                cleardevice();
                while(s<=ymax)
                {
                    ints(s);
                    sort(s);
                    s++;
                }
                break;
            case 2:
                exit(0);
        }

        cout<<"Do you want to continue?: ";
        cin>>ch;
    }while(ch=='y' || ch=='Y');
}

void poly::ints(float z) //DEFINE FUNCTION INTS
{
    int x1,x2,y1,y2,temp;
    c=0;
    for(int i=0;i<v;i++)
    {
        x1=p[i].x;
        y1=p[i].y;
        x2=p[i+1].x;
        y2=p[i+1].y;
        if(y2<y1)
        {
            temp=x1;
            x1=x2;
            x2=temp;
            temp=y1;
            y1=y2;
            y2=temp;
        }
        if(z<=y2&&z>=y1)
        {
            if((y1-y2)==0)
            x=x1;
            else // used to make changes in x. so that we can fill our polygon after cerain distance
            {
                x=((x2-x1)*(z-y1))/(y2-y1);
                x=x+x1;
            }
            if(x<=xmax && x>=xmin)
            inter[c++]=x;
        }
    }
}

void poly::sort(int z) //SORT FUNCTION
{
    int temp,j,i;

        for(i=0;i<v;i++)
        {
            line(p[i].x,p[i].y,p[i+1].x,p[i+1].y); // used to make hollow outlines of a polygon
        }
        delay(100);
        for(i=0; i<c;i+=2)
        {
            delay(100);
            line(inter[i],z,inter[i+1],z);  // Used to fill the polygon ....
        }
}

int main() //START OF MAIN
{
    int cl;
    initwindow(500,600);
    cleardevice();
    poly x;
    x.read();
    x.calcs();
    cleardevice();
    cout<<"\n\tEnter the colour u want:(0-15)->"; //Selecting colour
    cin>>cl;
    setcolor(cl);
    x.display();
    closegraph(); //CLOSE OF GRAPH
    getch();
    return 0;
}

// Output of the above program


Fill a Polygon Using Scan Line Fill Algorithm in C++
Fill a Polygon Using Scan Line Fill Algorithm in C++

Fill a Polygon Using Scan Line Fill Algorithm in C++
Fill a Polygon Using Scan Line Fill Algorithm in C++

Fill a Polygon Using Scan Line Fill Algorithm in C++
Fill a Polygon Using Scan Line Fill Algorithm in C++


Checkout this video on Polygon Filling Using Scan Line Fill Algorithm Using C++ in CodeBlocks 13.12...

7 comments:

  1. i have erorr :
    delay(); ,cleardevice(); , initwindow(); , setcolor(); , closegraph();
    and line();
    undefined

    ReplyDelete
    Replies
    1. There might be several reasons for this error. I think you can mail me the code and other details (like which compiler you are using, any other important thing which you think might be useful).

      Delete
  2. I have error for coordinates:
    p[0].x=100;
    p[0].y=100;
    p[1].x=150;
    p[1].y=130;
    p[2].x=200;
    p[2].y=110;
    p[3].x=200;
    p[3].y=200;
    p[4].x=150;
    p[4].y=150;
    p[5].x=100;
    p[5].y=200;

    It does not work well.

    ReplyDelete
  3. Thanks for sharing this algo! It is so simple, beautiful! Since sort() is called multiple times and always draw the outline of the polygon, is it possible the outline gets redrawn over and over with this implementation?

    ReplyDelete
  4. Is this implementation guaranteed to work for simple convex polygons?

    ReplyDelete
  5. s=ymin+0.01 why 0.01is added to ymin

    ReplyDelete
  6. i have an error in void poly::sort (int z)
    qualified-id in declaration before '(' token

    ReplyDelete