From 217fd7045ed54d5df7cdd13c9ac6a488e9237ead Mon Sep 17 00:00:00 2001
From: Erich Schubert <erich.schubert@tu-dortmund.de>
Date: Sat, 9 Nov 2024 23:14:20 +0100
Subject: [PATCH] collision fixes

---
 src/collision.cpp | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/collision.cpp b/src/collision.cpp
index 87c091515689d..355703ed785b9 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -33,7 +33,8 @@ struct NearbyCollisionInfo {
 		position(pos),
 		bouncy(bouncy),
 		is_unloaded(is_ul),
-		is_step_up(false)
+		is_step_up(false),
+		has_collided(false)
 	{}
 
 	// object
@@ -42,7 +43,8 @@ struct NearbyCollisionInfo {
 		box(box),
 		bouncy(bouncy),
 		is_unloaded(false),
-		is_step_up(false)
+		is_step_up(false),
+		has_collided(false)
 	{}
 
 	inline bool isObject() const { return obj != nullptr; }
@@ -50,9 +52,14 @@ struct NearbyCollisionInfo {
 	ActiveObject *obj;
 	aabb3f box;
 	v3s16 position;
+	f32 distance;
 	u8 bouncy;
 	// bitfield to save space
-	bool is_unloaded:1, is_step_up:1;
+	bool is_unloaded:1, is_step_up:1, has_collided:1;
+
+	bool operator<(const NearbyCollisionInfo& b) {
+		return distance < b.distance;
+	}
 };
 
 // Helper functions:
@@ -407,12 +414,19 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		add_object_boxes(env, box_0, dtime, *pos_f, aspeed_f, self, cinfo);
 	}
 
+	// Sort boxes by distance once, as we are more likely to collide with near boxes
+	v3f center_0 = box_0.getCenter();
+	for (auto box = cinfo.begin(); box != cinfo.end(); box++) {
+		box->distance = (box->box.getCenter() - center_0).getLengthSQ();
+	}
+	std::sort(cinfo.begin(), cinfo.end());
+
 	// Collision detection
 	f32 d = 0.0f;
 	for (int loopcount = 0;; loopcount++) {
 		if (loopcount >= 100) {
 			warningstream << "collisionMoveSimple: Loop count exceeded, aborting to avoid infinite loop" << std::endl;
-			g_collision_problems_encountered = true;
+			g_collision_problems_encountered = true; // for unit tests
 			break;
 		}
 
@@ -428,7 +442,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		for (u32 boxindex = 0; boxindex < cinfo.size(); boxindex++) {
 			const NearbyCollisionInfo &box_info = cinfo[boxindex];
 			// Ignore if already stepped up this nodebox.
-			if (box_info.is_step_up)
+			if (box_info.is_step_up || box_info.has_collided)
 				continue;
 
 			// Find nearest collision of the two boxes (raytracing-like)
@@ -454,6 +468,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		}
 		// Otherwise, a collision occurred.
 		NearbyCollisionInfo &nearest_info = cinfo[nearest_boxindex];
+		nearest_info.has_collided = true;
 		const aabb3f& cbox = nearest_info.box;
 
 		//movingbox except moved to the horizontal position it would be after step up
@@ -555,7 +570,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 			}
 			result.collides = true;
 		} else {
-			is_collision = false;
+			is_collision = false; // unreachable, actually
 		}
 
 		info.new_speed = *speed_f;
@@ -595,7 +610,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 				cbox.MaxEdge.Z - d > box.MinEdge.Z &&
 				cbox.MinEdge.Z + d < box.MaxEdge.Z) {
 			if (box_info.is_step_up) {
-				pos_f->Y += cbox.MaxEdge.Y - box.MinEdge.Y;
+				pos_f->Y += cbox.MaxEdge.Y - box.MinEdge.Y + 0.01f; // avoid glitching into the floor
 				box = box_0;
 				box.MinEdge += *pos_f;
 				box.MaxEdge += *pos_f;