sneak/Shared/Geometry.cs

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C#
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using Microsoft.Xna.Framework;
using System;
// Design largely from https://noonat.github.io/intersect/.
namespace SemiColinGames {
// Math functions that return floats rather than doubles, for convenience.
public static class FMath {
public const float PI = (float) Math.PI;
private readonly static float[] degToRad = new float[360];
static FMath() {
for (int i = 0; i < degToRad.Length; i++) {
degToRad[i] = PI / 180 * i;
}
}
// Converts degrees to radians using a look-up table. Expects the input to be near [0, 360)
// and will loop for potentially a long while if that's not the case.
public static float DegToRad(int degrees) {
while (degrees < 0) {
degrees += 360;
}
while (degrees >= 360) {
degrees -= 360;
}
return degToRad[degrees];
}
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public static float Sin(double radians) {
return (float) Math.Sin(radians);
}
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public static float Cos(double radians) {
return (float) Math.Cos(radians);
}
public static T Clamp<T>(T value, T min, T max) where T : IComparable {
if (value.CompareTo(min) == -1) {
return min;
} else if (value.CompareTo(max) == 1) {
return max;
} else {
return value;
}
}
}
public readonly struct Hit {
public readonly AABB Collider;
public readonly Vector2 Position;
public readonly Vector2 Delta;
public readonly Vector2 Normal;
public readonly float Time; // ranges from [0, 1].
public Hit(AABB collider, Vector2 position, Vector2 delta, Vector2 normal) :
this(collider, position, delta, normal, 0.0f) {
}
public Hit(AABB collider, Vector2 position, Vector2 delta, Vector2 normal, float time) {
Collider = collider;
Position = position;
Delta = delta;
Normal = normal;
Time = time;
}
public static bool operator ==(Hit a, Hit b) {
return a.Position == b.Position && a.Delta == b.Delta && a.Normal == b.Normal
&& a.Time == b.Time && a.Collider == b.Collider;
}
public static bool operator !=(Hit a, Hit b) {
return !(a == b);
}
public override bool Equals(object o) {
return o is Hit h && this == h;
}
public override int GetHashCode() {
return (Collider, Position, Delta, Normal, Time).GetHashCode();
}
}
public readonly struct Sweep {
public readonly Hit? Hit;
public readonly Vector2 Position;
public readonly float Time;
public Sweep(Hit? hit, Vector2 position, float time) {
Hit = hit;
Position = position;
Time = time;
}
public static bool operator ==(Sweep a, Sweep b) {
return a.Hit == b.Hit && a.Position == b.Position && a.Time == b.Time;
}
public static bool operator !=(Sweep a, Sweep b) {
return !(a == b);
}
public override bool Equals(object o) {
return o is Sweep s && this == s;
}
public override int GetHashCode() {
return (Hit, Position, Time).GetHashCode();
}
}
public readonly struct AABB {
public readonly Vector2 Position; // centroid
public readonly Vector2 HalfSize;
public readonly Tile Tile;
public AABB(Vector2 position, Vector2 halfSize) : this(position, halfSize, null) {
}
public AABB(Vector2 position, Vector2 halfSize, Tile tile) {
Position = position;
HalfSize = halfSize;
Tile = tile;
}
public static bool operator ==(AABB a, AABB b) {
return a.Position == b.Position && a.HalfSize == b.HalfSize && a.Tile == b.Tile;
}
public static bool operator !=(AABB a, AABB b) {
return !(a == b);
}
public override bool Equals(object o) {
return o is AABB a && this == a;
}
public override int GetHashCode() {
return (Position, HalfSize, Tile).GetHashCode();
}
public float Top {
get { return Position.Y - HalfSize.Y; }
}
public float Bottom {
get { return Position.Y + HalfSize.Y; }
}
public float Left {
get { return Position.X - HalfSize.X; }
}
public float Right {
get { return Position.X + HalfSize.X; }
}
public Vector2 TopLeft {
get { return new Vector2(Left, Top); }
}
public Vector2 TopRight {
get { return new Vector2(Right, Top); }
}
public Vector2 BottomLeft {
get { return new Vector2(Left, Bottom); }
}
public Vector2 BottomRight {
get { return new Vector2(Right, Bottom); }
}
public Hit? Intersect(AABB box) {
float dx = box.Position.X - Position.X;
float px = box.HalfSize.X + HalfSize.X - Math.Abs(dx);
if (px <= 0) {
return null;
}
float dy = box.Position.Y - Position.Y;
float py = box.HalfSize.Y + HalfSize.Y - Math.Abs(dy);
if (py <= 0) {
return null;
}
if (px < py) {
int sign = Math.Sign(dx);
Vector2 delta = new Vector2(px * sign, 0);
Vector2 normal = new Vector2(sign, 0);
Vector2 hitPos = new Vector2(Position.X + HalfSize.X * sign, box.Position.Y);
return new Hit(box, hitPos, delta, normal);
} else {
int sign = Math.Sign(dy);
Vector2 delta = new Vector2(0, py * sign);
Vector2 normal = new Vector2(0, sign);
Vector2 hitPos = new Vector2(box.Position.X, Position.Y + HalfSize.Y * sign);
return new Hit(this, hitPos, delta, normal);
}
}
public Hit? IntersectSegment(Vector2 pos, Vector2 delta) {
return IntersectSegment(pos, delta, Vector2.Zero);
}
public Hit? IntersectSegment(Vector2 pos, Vector2 delta, Vector2 padding) {
float scaleX = 1.0f / delta.X;
float scaleY = 1.0f / delta.Y;
int signX = Math.Sign(scaleX);
int signY = Math.Sign(scaleY);
float nearTimeX = (Position.X - signX * (HalfSize.X + padding.X) - pos.X) * scaleX;
float nearTimeY = (Position.Y - signY * (HalfSize.Y + padding.Y) - pos.Y) * scaleY;
float farTimeX = (Position.X + signX * (HalfSize.X + padding.X) - pos.X) * scaleX;
float farTimeY = (Position.Y + signY * (HalfSize.Y + padding.Y) - pos.Y) * scaleY;
if (nearTimeX > farTimeY || nearTimeY > farTimeX) {
return null;
}
float nearTime = Math.Max(nearTimeX, nearTimeY);
float farTime = Math.Min(farTimeX, farTimeY);
if (nearTime >= 1 || farTime <= 0) {
return null;
}
// If we've gotten this far, a collision is happening. If the near time is greater than zero,
// the segment starts outside and is entering the box. Otherwise, the segment starts inside
// the box, so we set the hit time to zero.
float hitTime = Math.Max(0, nearTime);
Vector2 normal = nearTimeX > nearTimeY ?
new Vector2(-signX, 0) :
new Vector2(0, -signY);
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Vector2 hitDelta = Vector2.Multiply(delta, -(1.0f - hitTime));
Vector2 hitPos = Vector2.Add(pos, Vector2.Multiply(delta, hitTime));
return new Hit(this, hitPos, hitDelta, normal, hitTime);
}
public Sweep Sweep(AABB box, Vector2 delta) {
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// Fast-path case if the other box is static.
if (delta.X == 0 && delta.Y == 0) {
Hit? staticHit = Intersect(box);
// TODO: I don't understand the original source here, but I think this is correct.
return new Sweep(staticHit, box.Position, staticHit?.Time ?? 1);
}
Hit? maybeHit = IntersectSegment(box.Position, delta, box.HalfSize);
if (maybeHit == null) {
return new Sweep(null, Vector2.Add(box.Position, delta), 1);
}
Hit hit = (Hit) maybeHit;
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Vector2 hitPos = Vector2.Add(box.Position, Vector2.Multiply(delta, hit.Time));
// TODO: why is this calculation made, and then thrown away?
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// Vector2 direction = Vector2.Normalize(delta);
// Vector2 sweepHitPos = new Vector2(
// FMath.Clamp(hit.Position.X + direction.X * box.HalfSize.X,
// Position.X - HalfSize.X,
// Position.X + HalfSize.X),
// FMath.Clamp(hit.Position.Y + direction.Y * box.HalfSize.Y,
// Position.Y - HalfSize.Y,
// Position.Y + HalfSize.Y));
return new Sweep(hit, hitPos, hit.Time);
}
}
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}