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line clipping algo problems

Discussion in 'MFC' started by canatan, Nov 22, 2009.

  1. canatan

    canatan New Member

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    i can not figure out where i'm going wrong with this algo. its supposed to clip lines using the cohen-sutherland line clipping technique..
    i'm pasting the various functions and code.. please help...
    abrl[] are arrays.
    xmax, ymax, xmin, ymin are the coordinates of the window.
    abrl[0]==1 if coordinate is left of window,
    abrl[1]==1 if coordinate is right
    abrl[2]==1 if below
    abrl[3]==1 if above..
    if both abrl of both the coordinates are 0 then we draw the line
    otherwise if by and-ing the arbl bits we get a 1 at any bit we dont draw the line
    in the third case we find the interesection of the line with max and min of the window till we get to condition 1 or 2
    Code:
    void Clineclipping1View::intersection(int &x1, int &y1, double m, double c, bool abrl[])
    {
    	if(abrl[0]==1)
    	{
    		y1=ymax;
    		x1=((ymax-c)/m);
    	}
    	else if(abrl[1]==1)
    	{
    		y1=ymin;
    		x1=((ymin-c)/m);
    	}
    	else if(abrl[2]==1)
    	{
    		x1=xmax;
    		y1=((m*xmax)+c);
    	}
    	else if(abrl[3]==1)
    	{
    		x1=xmin;
    		y1=((m*xmin)+c);
    	}
    
    }
    
    void Clineclipping1View::clipline(int x1, int y1, int x2, int y2,CDC *pDC)
    {int count=0;
    int px1=x1;
    int px2=x2;
    int py1=y1;
    int py2=y2;
    draw=false;
    done=false;
    float m=(y2-y1)/(x2-x1);
    float c= (y1-(m*x1));
    
    while(!done)
    {
    	regioncode(px1,py1,abrl1);
    	regioncode(px2,py2,abrl2);
    //line outside check
    for(int i=0;i<4;i++)
    {
    	if(abrl1[i]==1)
    		if(abrl2[i]==1)
    			count++;
    }
    if (count==4)
    {
    	draw=false;
    	done=true;
    }
    //line inside check
    count=0;
    for(int i=0;i<4;i++)
    {
    	if((abrl1[i]|abrl2[i])==0)
    		count++;
    }
    if(count==4)
    {
    	draw=true;
    	done=true;
    }
    if(!done)
    {intersection(px1,py1,m,c,abrl1);
    intersection(px2,py2,m,c,abrl2);
    }
    }
    if(done)
    {
    	if(draw)
    	{
    		pDC->MoveTo(px1,py1);
    		pDC->LineTo(px2,py2);
    	}
    
    		
    }
    }
    
    Code:
    void Clineclipping1View::intersection(int &x1, int &y1, double m, double c, bool abrl[])
    {
    	if(abrl[0]==1)
    	{
    		y1=ymax;
    		x1=((ymax-c)/m);
    	}
    	else if(abrl[1]==1)
    	{
    		y1=ymin;
    		x1=((ymin-c)/m);
    	}
    	else if(abrl[2]==1)
    	{
    		x1=xmax;
    		y1=((m*xmax)+c);
    	}
    	else if(abrl[3]==1)
    	{
    		x1=xmin;
    		y1=((m*xmin)+c);
    	}
    
    }
    Code:
    void Clineclipping1View::regioncode(int x1, int x2, bool abrl[])
    {
    	for(int i=0;i<4;i++)
    		abrl[i]=0;
    	if((x1-xmin)<0)	
    		abrl[3]=1;
    	else if((xmax-x1)<0)
    		abrl[2]=1;
    	if((x2-ymin)<0)
    		abrl[1]=1;
    	else if((ymax-x2)<0)
    		abrl[0]=1;
    
    	
    }
     

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