[CITATION][C] A note on multi-polygon area filling
JR Rankin - Computers & graphics, 1987 - Elsevier
After drawing each trapezium, common edges must be corrected again. A line needs to be
corrected (ie, redrawn in XOR mode) only if the sign of (Xk--Xj) equals the sign of (xj-xi)
where k=[(j+ 1) mod n]+ 1 andj=[(i+ 1) mod n]+ 1.(See Fig. 2.) However, here the common
edges are all vertical and for these there is never a difference between line pixels and
trapezium edge pixels. This algorithm, therefore, relies on a valid trapezium fill algorithm.
Like the triangle, the trapezium is never concave, and an algorithm to area fill a trapezium …
corrected (ie, redrawn in XOR mode) only if the sign of (Xk--Xj) equals the sign of (xj-xi)
where k=[(j+ 1) mod n]+ 1 andj=[(i+ 1) mod n]+ 1.(See Fig. 2.) However, here the common
edges are all vertical and for these there is never a difference between line pixels and
trapezium edge pixels. This algorithm, therefore, relies on a valid trapezium fill algorithm.
Like the triangle, the trapezium is never concave, and an algorithm to area fill a trapezium …
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