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