CG/Assignment A-1 (Scan Line Fill).cpp

/* Define the structure to store the edges*/
#include<iostream>
#include<graphics.h>
using namespace std;
struct edge{
	int x1,y1,x2,y2,flag;
};
int main()
{
	int gd=DETECT,gm,n,i,j,k;
	struct edge ed[10],temped;
	float dx,dy,m[10],x_int[10],inter_x[10];
	int x[10],y[10],ymax=0,ymin=480,yy,temp;
	initgraph(&gd,&gm,NULL);
	
/*read the number of vertices of the polygon*/
	cout<<"Enter the no.of vertices of the graph :";
	cin>>n;
	
/*read the vertices of the polygon and also find ymax and ymin*/
	cout<<"Enter the vertices";
	for(i=0;i<n;i++)
	{
		cin>>x[i];
		cin>>y[i];
		if(y[i]>ymax)
			ymax=y[i];
		if(y[i]<ymin)
			ymin=y[i];
		ed[i].x1=x[i];
		ed[i].y1=y[i];
	}
	

/*store the edge information*/
	cout<<"\nEdge Information\n";
	for(i=0;i<n-1;i++)
	  {
		ed[i].x2=ed[i+1].x1;
		ed[i].y2=ed[i+1].y1;
		ed[i].flag=0;
          cout<<"("<<ed[i].x1<<", "<<ed[i].y1<<") ("<<ed[i].x2<<", "<<ed[i].y2<<")"<<endl;
	  }
          ed[i].x2=ed[0].x1;
	     ed[i].y2=ed[0].y1;
	     ed[i].flag=0;
	     cout<<"("<<ed[i].x1<<", "<<ed[i].y1<<") ("<<ed[i].x2<<", "<<ed[i].y2<<")"<<endl;
	

/*Check for y1>y2, if not interchnge y1 and y2 */
	cout<<"\nUpdated Edge Information\n";
	for(i=0;i<n;i++)
	{
		if(ed[i].y1 < ed[i].y2)
		{
			temp=ed[i].x1;
			ed[i].x1=ed[i].x2;
			ed[i].x2=temp;
			temp=ed[i].y1;
			ed[i].y1=ed[i].y2;
			ed[i].y2=temp;
		}
		cout<<"("<<ed[i].x1<<", "<<ed[i].y1<<") ("<<ed[i].x2<<", "<<ed[i].y2<<")"<<endl;
	}
	

/*Draw the polygon*/
	for(i=0;i<n;i++)
	{
		line(ed[i].x1, ed[i].y1,ed[i].x2,ed[i].y2);
	}

	
/*calculating 1/slope of each edge*/
	for(i=0;i<n;i++)
	{
		dx=ed[i].x2-ed[i].x1;
		dy=ed[i].y2-ed[i].y1;
		if(dy==0)
		{
			m[i]=0;
		}
		else
		{
			m[i]=dx/dy;
		}
		inter_x[i]=ed[i].x1;
	}
	
	yy=ymax;

	//Working with Active edges
	while(yy>ymin)
	{
		//cout<<"\n\t"<<yy;
		for(i=0;i<n;i++)
		{
			if(yy>ed[i].y2 && yy<=ed[i].y1)
				ed[i].flag=1;               //Active edge
			else
				ed[i].flag=0;              //not Active edge
		}
		j=0;
		for(i=0;i<n;i++)
		{
			if(ed[i].flag==1)
			{
				if(yy==ed[i].y1)
				{
					x_int[j]=ed[i].x1;
					j++;
                    }
				else
				{
					x_int[j]=inter_x[i]+(-m[i]);
					inter_x[i]=x_int[j];
					j++;
				}
			}
		}


		/*sorting the x intersection*/
		for(i=0;i<j;i++)
		{
			for(k=0;k<j-1;k++)
			{
				if(x_int[k]>x_int[k+1])
				{
					temp=(int)x_int[k];
					x_int[k]=x_int[k+1];
					x_int[k+1]=temp;
				}
			}
		}


		/*extracting pairs of values to draw lilnes*/
		for(i=0;i<j;i=i+2)
		{    setcolor(GREEN);
			line((int)x_int[i],yy,(int)x_int[i+1],yy);
		}
		yy--;
		delay(50);
	}//while
	delay(10000);
	closegraph();
}



/*
Enter the vertices 80 20 100 80 150 60 130 200 40 250
*/