Theory
In Liang-Barsky algorithm, we first write the point-clipping conditions in parametric form as
Each of these for inequalities can be expressed as
, k = 1, 2, 3, …..
where parameter p and q are defined as
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In Liang-Barsky algorithm, we first write the point-clipping conditions in parametric form as
Each of these for inequalities can be expressed as
, k = 1, 2, 3, …..where parameter p and q are defined as
Any line that is parallel to one of the clipping boundaries has pk = 0 for the value of k corresponding to that boundary. If, for that value of k, we also find qk < 0, then the line is completely outside the boundary and can be eliminated from further consideration. If qk >=0, the line is inside the parallel clipping boundary.
When pk <0, the infinite extension of the line proceeds from the outside to the inside of the inside of the infinite extension of this particular boundary. If pk > 0, the line proceeds from the insides to the outside. For a nonzero value of pk, we can calculate the value of u that corresponds to the point where the infinitely extended line intersects the extension of boundary k as u = qk / pk.
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