Help with Visibility Polygon Creation Pre-loop Behavior

[hawkinsw]

In the startup to the visibility polygon calculation function, you insert the incident edge to the first vertex encountered on the CCW sweep (

VisiLibity1/src/visilibity.cpp

Line 2710 in d95c801

// Insert e into q2 as long as it doesn't contain the

). In the two published versions of the algorithm (the TR and the conference article), I cannot find this behavior. In one version, no points are initially pushed into q2. In the other version, the edges whose starting vertex is exactly horizontal to the observer are all inserted into q2, except for the first edge. I am sure that what you are doing is correct, but I cannot wrap my head around the reasoning and would appreciate a tutorial if you had a minute.