From 200058a61160bf3ec305bf871c97dd4431fcab57 Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Sun, 7 Mar 2021 22:03:29 +0100
Subject: [PATCH] added a method to make sidescrolling collision detection
 easier with TiledMapCollisions

---
 MLEM.Extended/Extensions/NumberExtensions.cs |  7 ++++++
 MLEM.Extended/Tiled/TiledMapCollisions.cs    | 26 ++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/MLEM.Extended/Extensions/NumberExtensions.cs b/MLEM.Extended/Extensions/NumberExtensions.cs
index 94d4fb2..b85f9a4 100644
--- a/MLEM.Extended/Extensions/NumberExtensions.cs
+++ b/MLEM.Extended/Extensions/NumberExtensions.cs
@@ -1,3 +1,5 @@
+using Microsoft.Xna.Framework;
+using MLEM.Extensions;
 using MonoGame.Extended;
 
 namespace MLEM.Extended.Extensions {
@@ -24,5 +26,10 @@ namespace MLEM.Extended.Extensions {
             return new Misc.RectangleF(rect.X, rect.Y, rect.Width, rect.Height);
         }
 
+        /// <inheritdoc cref="MLEM.Extensions.NumberExtensions.Penetrate"/>
+        public static bool Penetrate(this RectangleF rect, RectangleF other, out Vector2 normal, out float penetration) {
+            return rect.ToMlem().Penetrate(other.ToMlem(), out normal, out penetration);
+        }
+
     }
 }
\ No newline at end of file
diff --git a/MLEM.Extended/Tiled/TiledMapCollisions.cs b/MLEM.Extended/Tiled/TiledMapCollisions.cs
index 563ddf7..91cad36 100644
--- a/MLEM.Extended/Tiled/TiledMapCollisions.cs
+++ b/MLEM.Extended/Tiled/TiledMapCollisions.cs
@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.Xna.Framework;
+using MLEM.Extended.Extensions;
 using MLEM.Extensions;
 using MLEM.Misc;
 using MonoGame.Extended.Tiled;
@@ -110,6 +111,31 @@ namespace MLEM.Extended.Tiled {
             return this.GetCollidingTiles(area, included).Any();
         }
 
+        /// <summary>
+        /// Returns a set of normals and penetration amounts for each <see cref="TileCollisionInfo"/> that intersects with the given <see cref="RectangleF"/> area.
+        /// The normals and penetration amounts are based on <see cref="MLEM.Extensions.NumberExtensions.Penetrate"/>.
+        /// Note that all x penetrations are returned before all y penetrations, which improves collision detection in sidescrolling games with gravity.
+        /// </summary>
+        /// <param name="getArea">The area to penetrate</param>
+        /// <returns>A set of normals and penetration amounts</returns>
+        public IEnumerable<(Vector2, float)> GetPenetrations(Func<RectangleF> getArea) {
+            foreach (var col in this.GetCollidingAreas(getArea())) {
+                if (getArea().Penetrate(col, out var normal, out var penetration) && normal.X != 0)
+                    yield return (normal, penetration);
+            }
+            foreach (var col in this.GetCollidingAreas(getArea())) {
+                if (getArea().Penetrate(col, out var normal, out var penetration) && normal.Y != 0)
+                    yield return (normal, penetration);
+            }
+        }
+
+        private IEnumerable<RectangleF> GetCollidingAreas(RectangleF area, Func<TileCollisionInfo, bool> included = null) {
+            foreach (var tile in this.GetCollidingTiles(area, included)) {
+                foreach (var col in tile.Collisions)
+                    yield return col;
+            }
+        }
+
         /// <summary>
         /// A delegate method used to override the default collision checking behavior.
         /// </summary>