MoonTools.Bonk/Bonk/AABB.cs

147 lines
4.4 KiB
C#

using System;
using System.Collections.Generic;
using System.Numerics;
using MoonTools.Structs;
namespace MoonTools.Bonk
{
/// <summary>
/// Axis-aligned bounding box.
/// </summary>
public struct AABB : IEquatable<AABB>
{
/// <summary>
/// The top-left position of the AABB.
/// </summary>
/// <value></value>
public Vector2 Min { get; private set; }
/// <summary>
/// The bottom-right position of the AABB.
/// </summary>
/// <value></value>
public Vector2 Max { get; private set; }
public float Width { get { return Max.X - Min.X; } }
public float Height { get { return Max.Y - Min.Y; } }
public float Right { get { return Max.X; } }
public float Left { get { return Min.X; } }
/// <summary>
/// The top of the AABB. Assumes a downward-aligned Y axis, so this value will be smaller than Bottom.
/// </summary>
/// <value></value>
public float Top { get { return Min.Y; } }
/// <summary>
/// The bottom of the AABB. Assumes a downward-aligned Y axis, so this value will be larger than Top.
/// </summary>
/// <value></value>
public float Bottom { get { return Max.Y; } }
public AABB(float minX, float minY, float maxX, float maxY)
{
Min = new Vector2(minX, minY);
Max = new Vector2(maxX, maxY);
}
public AABB(Vector2 min, Vector2 max)
{
Min = min;
Max = max;
}
private static Matrix3x2 AbsoluteMatrix(Matrix3x2 matrix)
{
return new Matrix3x2
(
Math.Abs(matrix.M11), Math.Abs(matrix.M12),
Math.Abs(matrix.M21), Math.Abs(matrix.M22),
Math.Abs(matrix.M31), Math.Abs(matrix.M32)
);
}
/// <summary>
/// Efficiently transforms the AABB by a Transform2D.
/// </summary>
/// <param name="aabb"></param>
/// <param name="transform"></param>
/// <returns></returns>
public static AABB Transformed(AABB aabb, Transform2D transform)
{
var center = (aabb.Min + aabb.Max) / 2f;
var extent = (aabb.Max - aabb.Min) / 2f;
var newCenter = Vector2.Transform(center, transform.TransformMatrix);
var newExtent = Vector2.TransformNormal(extent, AbsoluteMatrix(transform.TransformMatrix));
return new AABB(newCenter - newExtent, newCenter + newExtent);
}
/// <summary>
/// Creates an AABB for an arbitrary collection of positions.
/// This is less efficient than defining a custom AABB method for most shapes, so avoid using this if possible.
/// </summary>
/// <param name="vertices"></param>
/// <returns></returns>
public static AABB FromVertices(IEnumerable<Position2D> vertices)
{
var minX = float.MaxValue;
var minY = float.MaxValue;
var maxX = float.MinValue;
var maxY = float.MinValue;
foreach (var vertex in vertices)
{
if (vertex.X < minX)
{
minX = vertex.X;
}
if (vertex.Y < minY)
{
minY = vertex.Y;
}
if (vertex.X > maxX)
{
maxX = vertex.X;
}
if (vertex.Y > maxY)
{
maxY = vertex.Y;
}
}
return new AABB(minX, minY, maxX, maxY);
}
public static bool TestOverlap(AABB a, AABB b)
{
return a.Left <= b.Right && a.Right >= b.Left && a.Top <= b.Bottom && a.Bottom >= b.Top;
}
public override bool Equals(object obj)
{
return obj is AABB aabb && Equals(aabb);
}
public bool Equals(AABB other)
{
return Min == other.Min &&
Max == other.Max;
}
public override int GetHashCode()
{
return HashCode.Combine(Min, Max);
}
public static bool operator ==(AABB left, AABB right)
{
return left.Equals(right);
}
public static bool operator !=(AABB left, AABB right)
{
return !(left == right);
}
}
}