The algorithm considers several things:
(1) Whether the polygon is Convex or Concave.
(2) Whether the polygon is positively or negatively oriented.
(3) And, finally, testing polygon edges against the edges of the clipping window.
WXYZ as the clipping rectangle in the following picture.
I have several questions:
(1) Do I need to test an edge
AB against all of the edges of
wxyz or just
(2) Suppose, I test
wx. According to the Page-97 of the book, I should be testing whether it is on the left or on the right side of the clipping edge. But,in this case, there are no lefts or rights. There are aboves and bellows. How can I determine whether it is inside or outside?
(3) How can I keep track of the
Outside? For example, Consider the polygon edge
BC. If I test it against
ZW, it is on the Right side and Inside the Clipping Region. If I test it against
YX, it is on the Left side and Inside the Clipping Region. It turns out to me that, it is actually not possible to find the position of a point with respect to the clipping region unless we consider the region at once and as a whole. Then why is the book testing points against one line at a time?
(4) Consider the edge
DE. Is it going out or coming in?