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Minor performance optimisations in GeometryExtensions

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This commit is contained in:
BobLd
2024-06-28 21:18:38 +01:00
parent bac00e475b
commit 65c644f150
1 changed files with 113 additions and 52 deletions
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115
src/UglyToad.PdfPig/Geometry/GeometryExtensions.cs
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@@ -3,6 +3,7 @@
using System.Linq;
using System.Text;
using Core;
using System.Buffers;
using UglyToad.PdfPig.Geometry.ClipperLibrary;
using UglyToad.PdfPig.Graphics;
using static UglyToad.PdfPig.Core.PdfSubpath;
@@ -66,17 +67,19 @@
/// The vertices of P are assumed to be in strict cyclic sequential order, either clockwise or
/// counter-clockwise relative to the origin P0.
/// </param>
private static PdfRectangle ParametricPerpendicularProjection(IReadOnlyList<PdfPoint> polygon)
private static PdfRectangle ParametricPerpendicularProjection(ReadOnlySpan<PdfPoint> polygon)
{
if (polygon is null || polygon.Count == 0)
if (polygon.Length == 0)
{
throw new ArgumentException("ParametricPerpendicularProjection(): polygon cannot be null and must contain at least one point.", nameof(polygon));
}
else if (polygon.Count == 1)
if (polygon.Length == 1)
{
return new PdfRectangle(polygon[0], polygon[0]);
}
else if (polygon.Count == 2)
if (polygon.Length == 2)
{
return new PdfRectangle(polygon[0], polygon[1]);
}
@@ -110,7 +113,7 @@
double uX;
double uY;
for (j = 0; j < polygon.Count; j++)
for (j = 0; j < polygon.Length; j++)
{
Pj = polygon[j];
uX = Pj.X - Pk.X;
@@ -167,15 +170,23 @@
if (A < Amin)
{
Amin = A;
mrb = [R0X, R0Y, R1X, R1Y, R2X, R2Y, R3X, R3Y];
mrb[0] = R0X;
mrb[1] = R0Y;
mrb[2] = R1X;
mrb[3] = R1Y;
mrb[4] = R2X;
mrb[5] = R2Y;
mrb[6] = R3X;
mrb[7] = R3Y;
}
}
k++;
j = k + 1;
if (j == polygon.Count) j = 0;
if (k == polygon.Count) break;
if (j == polygon.Length) j = 0;
if (k == polygon.Length) break;
}
return new PdfRectangle(new PdfPoint(mrb[4], mrb[5]),
@@ -190,13 +201,28 @@
/// </summary>
/// <param name="points">The points.</param>
public static PdfRectangle MinimumAreaRectangle(IEnumerable<PdfPoint> points)
{
if (points is null)
{
throw new ArgumentException("MinimumAreaRectangle(): points cannot be null.", nameof(points));
}
return MinimumAreaRectangle(points.ToArray());
}
/// <summary>
/// Algorithm to find the (oriented) minimum area rectangle (MAR) by first finding the convex hull of the points
/// and then finding its MAR.
/// </summary>
/// <param name="points">The points.</param>
public static PdfRectangle MinimumAreaRectangle(PdfPoint[] points)
{
if (points?.Any() != true)
{
throw new ArgumentException("MinimumAreaRectangle(): points cannot be null and must contain at least one point.", nameof(points));
}
return ParametricPerpendicularProjection(GrahamScan(points.Distinct()).ToList());
return ParametricPerpendicularProjection(GrahamScan(points.Distinct()).ToArray());
}
/// <summary>
@@ -256,14 +282,37 @@
/// <summary>
/// Algorithm to find the convex hull of the set of points with time complexity O(n log n).
/// </summary>
public static IEnumerable<PdfPoint> GrahamScan(IEnumerable<PdfPoint> points)
public static IReadOnlyCollection<PdfPoint> GrahamScan(IEnumerable<PdfPoint> points)
{
if (points?.Any() != true)
{
throw new ArgumentException("GrahamScan(): points cannot be null and must contain at least one point.", nameof(points));
return GrahamScan(points.ToArray());
}
if (points.Count() < 3) return points;
private sealed class PdfPointXYComparer : IComparer<PdfPoint>
{
public static readonly PdfPointXYComparer Instance = new();
public int Compare(PdfPoint p1, PdfPoint p2)
{
int comp = p1.X.CompareTo(p2.X);
return comp == 0 ? p1.Y.CompareTo(p2.Y) : comp;
}
}
/// <summary>
/// Algorithm to find the convex hull of the set of points with time complexity O(n log n).
/// </summary>
public static IReadOnlyCollection<PdfPoint> GrahamScan(PdfPoint[] points)
{
if (points is null || points.Length == 0)
{
throw new ArgumentException("GrahamScan(): points cannot be null and must contain at least one point.",
nameof(points));
}
if (points.Length < 3)
{
return points;
}
static double polarAngle(in PdfPoint point1, in PdfPoint point2)
{
@@ -271,52 +320,64 @@
return Math.Atan2(point2.Y - point1.Y, point2.X - point1.X) % Math.PI;
}
var stack = new Stack<PdfPoint>();
var sortedPoints = points.OrderBy(p => p.X).ThenBy(p => p.Y).ToList();
var P0 = sortedPoints[0];
var groups = sortedPoints.Skip(1).GroupBy(p => polarAngle(P0, p)).OrderBy(g => g.Key);
Array.Sort(points, PdfPointXYComparer.Instance);
sortedPoints = new List<PdfPoint>();
foreach (var group in groups)
var P0 = points[0];
var groups = points.Skip(1).GroupBy(p => polarAngle(P0, p)).OrderBy(g => g.Key).ToArray();
var sortedPoints = ArrayPool<PdfPoint>.Shared.Rent(groups.Length);
try
{
for (int i = 0; i < groups.Length; i++)
{
var group = groups[i];
if (group.Count() == 1)
{
sortedPoints.Add(group.First());
sortedPoints[i] = group.First();
}
else
{
// if more than one point has the same angle,
// remove all but the one that is farthest from P0
sortedPoints.Add(group.OrderByDescending(p =>
sortedPoints[i] = group.OrderByDescending(p =>
{
double dx = p.X - P0.X;
double dy = p.Y - P0.Y;
return dx * dx + dy * dy;
}).First());
}).First();
}
}
if (sortedPoints.Count < 2)
if (groups.Length < 2)
{
return new[] { P0, sortedPoints[0] };
return [P0, sortedPoints[0]];
}
var stack = new Stack<PdfPoint>();
stack.Push(P0);
stack.Push(sortedPoints[0]);
stack.Push(sortedPoints[1]);
for (int i = 2; i < sortedPoints.Count; i++)
for (int i = 2; i < groups.Length; i++)
{
var point = sortedPoints[i];
while (stack.Count > 1 && !ccw(stack.ElementAt(1), stack.Peek(), point))
{
stack.Pop();
}
stack.Push(point);
}
return stack;
}
finally
{
ArrayPool<PdfPoint>.Shared.Return(sortedPoints);
}
}
#endregion
#region PdfRectangle
@@ -469,7 +530,7 @@
/// Gets the axis-aligned rectangle that completely containing the original rectangle, with no rotation.
/// </summary>
/// <param name="rectangle"></param>
public static PdfRectangle Normalise(this in PdfRectangle rectangle)
public static PdfRectangle Normalise(this PdfRectangle rectangle)
{
var bottomLeft = rectangle.BottomLeft;
var bottomRight = rectangle.BottomRight;