Cyrus–Beck algorithm

The Cyrus–Beck algorithm is a line clipping algorithm. It was designed to be more efficient than the Sutherland–Cohen algorithm which uses repetitive clipping . Cyrus–Beck is a general algorithm and can be used with a convex polygon clipping window unlike Sutherland-Cohen that can be used only on a rectangular clipping area.

Here the parametric equation of a line in the view plane is:

${\begin{aligned}p(t)&=&tp_{1}+(1-t)p_{0}\\&=&p_{0}+t(p_{1}-p_{0})\end{aligned}}$

where $0\leq t\leq 1$.

Now to find intersection point with the clipping window we calculate value of dot product. Let p_E be a point on the clipping plane E.

Calculate $n\cdot (p(t)-p_{E})$.

if > 0 vector pointed towards interior

if = 0 vector pointed parallel to plane containing p

if < 0 vector pointed away from interior

Here n stands for normal of the current clipping plane.

By this we select the point of intersection of line and clipping window where (dot product = 0 ) and hence clip the line.

See also

Algorithms used for the same purpose:

• Cohen-Sutherland
• Liang-Barsky
• Nicholl–Lee–Nicholl
• Fast-clipping

External links

• http://cs1.bradley.edu/public/jcm/cs535CyrusBeck.html
• http://softsurfer.com/Archive/algorithm_0111/algorithm_0111.htm