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Rewrite GetConvexHull

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kongehund 2024-09-14 16:32:51 +02:00
parent ff3bffc7d9
commit 385eb5eed5
1 changed files with 53 additions and 23 deletions
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76
osu.Game/Utils/GeometryUtils.cs
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@ -152,42 +152,72 @@ namespace osu.Game.Utils
/// <param name="points">The points to calculate a convex hull.</param>
public static List<Vector2> GetConvexHull(IEnumerable<Vector2> points)
{
List<Vector2> p = points.ToList();
// Naming convention implies positive y upwards.
if (p.Count < 3)
return p;
bool isCCW(Vector2 a, Vector2 b, Vector2 c) => crossProduct(b - a, c - a) > 0;
p.Sort((a, b) => a.X == b.X ? a.Y.CompareTo(b.Y) : a.X.CompareTo(b.X));
float crossProduct(Vector2 v1, Vector2 v2) => v1.X * v2.Y - v1.Y * v2.X;
List<Vector2> upper = new List<Vector2>();
List<Vector2> lower = new List<Vector2>();
var pointsList = points.ToList();
// Build the lower hull
for (int i = 0; i < p.Count; i++)
pointsList.Sort(delegate (Vector2 point1, Vector2 point2)
{
while (lower.Count >= 2 && cross(lower[^2], lower[^1], p[i]) <= 0)
lower.RemoveAt(lower.Count - 1);
if (point1.X == point2.X)
return point1.Y.CompareTo(point2.Y);
return point1.X.CompareTo(point2.X);
});
lower.Add(p[i]);
if (pointsList.Count < 3)
return pointsList;
var convexHullUpper = new List<Vector2>
{
pointsList[0],
pointsList[1]
};
var convexHullLower = new List<Vector2>
{
pointsList[pointsList.Count - 1],
pointsList[pointsList.Count - 2]
};
for (int i_points = 2; i_points < pointsList.Count; i_points++)
{
Vector2 c = pointsList[i_points];
for (int i_hull = convexHullUpper.Count - 1; i_hull > 0; i_hull--)
{
Vector2 a = convexHullUpper[^2];
Vector2 b = convexHullUpper[^1];
if (isCCW(a, b, c))
convexHullUpper.Remove(b);
else
break;
}
convexHullUpper.Add(c);
}
// Build the upper hull
for (int i = p.Count - 1; i >= 0; i--)
for (int i_points = pointsList.Count - 3; i_points >= 0; i_points--)
{
while (upper.Count >= 2 && cross(upper[^2], upper[^1], p[i]) <= 0)
upper.RemoveAt(upper.Count - 1);
upper.Add(p[i]);
Vector2 c = pointsList[i_points];
for (int i_hull = convexHullLower.Count - 1; i_hull > 0; i_hull--)
{
Vector2 a = convexHullLower[^2];
Vector2 b = convexHullLower[^1];
if (isCCW(a, b, c))
convexHullLower.Remove(b);
else
break;
}
convexHullLower.Add(c);
}
// Remove the last point of each half because it's a duplicate of the first point of the other half
lower.RemoveAt(lower.Count - 1);
upper.RemoveAt(upper.Count - 1);
convexHullUpper.RemoveAt(convexHullUpper.Count - 1);
convexHullLower.RemoveAt(convexHullLower.Count - 1);
lower.AddRange(upper);
return lower;
convexHullUpper.AddRange(convexHullLower);
var convexHull = convexHullUpper;
float cross(Vector2 o, Vector2 a, Vector2 b) => (a.X - o.X) * (b.Y - o.Y) - (a.Y - o.Y) * (b.X - o.X);
return convexHull;
}
public static List<Vector2> GetConvexHull(IEnumerable<IHasPosition> hitObjects) =>