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Improve performance of straight line edge case handling

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This commit is contained in:
karl 2020-12-06 19:56:16 +01:00
parent 82c0df1840
commit ef01f37834
1 changed files with 21 additions and 25 deletions
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46
Quickhull.h
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@ -113,42 +113,38 @@ private:
// If the input vector is empty, we're done
if (input.empty()) return;
// Find the point which is furthest away from the line, add it to the output
Point furthest_point;
// Find the points which are furthest away from the line
float furthest_distance = -1.0;
std::list<Point> furthest_points;
for (const Point &point : input)
{
float this_distance = line.distance_squared_to(point);
// It's possible for there to be multiple closests points (e.g. in the case)
// of a rectangle). We need to handle all these properly, so we make a list
// of all points at the furthest distance.
if (this_distance > furthest_distance)
{
furthest_distance = this_distance;
furthest_point = point;
furthest_points.clear();
furthest_points.emplace_back(point);
}
}
// TODO: e.g. in the case of a rectangle, it's possible for there to be
// multiple closest points (sometimes all at distance 0). How do we handle
// these properly? We definitely need to remove them all from input later;
// do we also need to handle them all further? This hotfix works, but seems
// like an unnecessarily big performance hit for that edge case.
for (const Point &point : input)
{
float this_distance = line.distance_squared_to(point);
if (this_distance == furthest_distance)
else if (this_distance == furthest_distance)
{
output.emplace_back(point);
furthest_points.emplace_back(point);
}
}
// Remove the previously checked points from the input -- we can't do that in
// the previous loop because we can't delete from the list we're iterating over
input.remove_if([furthest_distance, line](Point point)
{
return furthest_distance == line.distance_squared_to(point);
});
output.emplace_back(furthest_point);
input.remove(furthest_point);
for (const Point &point : furthest_points)
{
// All furthest points we found are part of the hull, so add them to the output
// and remove them from the input.
output.emplace_back(point);
input.remove(point);
}
Point furthest_point = furthest_points.front();
// Build a triangle with these 3 points
@ -159,7 +155,6 @@ private:
if (line.is_point_right(furthest_point))
{
// TOOD: It's probably more efficient to set the fields?
new_line1 = Line(line.to(), furthest_point);
new_line2 = Line(furthest_point, line.from());
}
@ -182,6 +177,8 @@ private:
{
left_of_line1.emplace_back(point);
}
// TODO: Are there any possible edge cases where this 'else if' won't work,
// and we need an 'if' instead?
else if (!new_line2.is_point_right(point))
{
left_of_line2.emplace_back(point);
@ -189,7 +186,6 @@ private:
}
// Recursively call get_hull_with_line for each side of the triangle
// TODO: We can skip the original one
get_hull_with_line(left_of_line1, output, new_line1);
get_hull_with_line(left_of_line2, output, new_line2);
}