LiangBarskyAlgorithm.cpp

#include"graphics.h" 
#define ROUND(a) ((int)(a+0.5)) 
int clipTest (float p,float q, float * tl, float * t2) 
{ 
float r ; 
int retVal = TRUE; 

//line entry point 
if (p < 0.0) {	 
	
	r = q /p ; 
	
	// line portion is outside the clipping edge 
	if ( r > *t2 )						 
	retVal = FALSE; 
	
	else
	if (r > *t1 ) 
	*tl = r; 
} 

else

//line leaving point 
if (p>0.0) {							 
	r = q/p ; 
	
	// line portion is outside	 
	if ( r<*t1 )						 
		retVal = FALSE;	 
		
	else i f (r<*t2) 
		*t2 = r; 
} 

// p = 0, so line is parallel to this clipping edge 
else	

// Line is outside clipping edge 
if (q<0.0)								 
retVal = FALSE; 

return ( retVal ) ; 
} 

void clipLine (dcPt winMin, dcPt winMax, wcPt2 pl , wcPt2 p2) 

{ 
float t1 = 0.0, t2 = 1.0, dx = p2.x-p1.x, dy; 

// inside test wrt left edge 
if(clipTest (-dx, p1.x - winMin.x, &t1, &t2))	 

// inside test wrt right edge 
if(clipTest (dx, winMax.x - p1.x, &t1, &t2)) 

{				 
	dy = p2.y - p1.y; 
	
	// inside test wrt bottom edge 
	if(clipTest (-dy, p1.y - winMin.y, &t1, &t2)) 
	
		// inside test wrt top edge 
		if(clipTest (dy, winMax.y - p1.y, &t1, &t2)) { 
			
		if(t2 < 1.0) { 
			p2.x = p1.x + t2*dx; 
			p2.y = p1.y + t2*dy; 
		} 
		
		if(t1 > 0.0) { 
			p1.x += t1*dx; 
			p1.y += t1*dy; 
		} 
		
		lineDDA ( ROUND(p1.x), ROUND(p1.y), ROUND(p2.x), ROUND(p2.y) ); 
		
		} 
} 

}