From fc011576a21251bd1e78c5f5e1104673f8712020 Mon Sep 17 00:00:00 2001
From: Michieru <Michieru@users.noreply.github.com>
Date: Sat, 4 Oct 2014 10:46:42 +0200
Subject: Pathfinding now works exactly as on the client

- This should solve most of the position lag problems, especially ones that caused monsters to suddenly appear next to you (happened especially often when using icewall)
- Added a new heap implementation to db.h (POP2, PUSH2, SIFTUP, SIFTDOWN, UPDATE) that simulates the heap that the client uses, there was no other way to reproduce 100% exact behavior
- I recommend using the old heap implementation for everything else
- Updated path.c to use the new heap macros and also fixed the order in which the different possible directions are pushed into heap
- Special thanks to rversteegen for helping me with various tests and the heap implementation
- Special thanks to ultramage for providing info that helped us narrowing down the possible variables

Mega thanks to Playtester (rathena:c009b3f4a)
---
 src/common/db.h | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)

(limited to 'src/common/db.h')

diff --git a/src/common/db.h b/src/common/db.h
index bf59e37d6..f807188eb 100644
--- a/src/common/db.h
+++ b/src/common/db.h
@@ -1347,6 +1347,7 @@ void  linkdb_foreach (struct linkdb_node** head, LinkDBFunc func, ...);
 /////////////////////////////////////////////////////////////////////
 // Binary heap library based on defines. (uses the vector defines above)
 // uses aMalloc, aRealloc, aFree
+// WARNING: BHEAP implementation details affect behaviour of A* pathfinding
 
 
 
@@ -1459,6 +1460,21 @@ void  linkdb_foreach (struct linkdb_node** head, LinkDBFunc func, ...);
 
 
 
+/// See BHEAP_PUSH. Version used by A* implementation, matching client bheap.
+///
+/// @param __heap Binary heap
+/// @param __val Value
+/// @param __topcmp Comparator
+/// @param __swp Swapper
+#define BHEAP_PUSH2(__heap,__val,__topcmp,__swp) \
+	do{ \
+		size_t _i_ = VECTOR_LENGTH(__heap); \
+		VECTOR_PUSH(__heap,__val); /* insert at end */ \
+		BHEAP_SIFTDOWN(__heap,0,_i_,__topcmp,__swp); \
+	}while(0)
+
+
+
 /// Removes the top value of the heap. (using the '=' operator)
 /// Assumes the heap is not empty.
 ///
@@ -1474,6 +1490,21 @@ void  linkdb_foreach (struct linkdb_node** head, LinkDBFunc func, ...);
 
 
 
+/// See BHEAP_POP. Version used by A* implementation, matching client bheap.
+///
+/// @param __heap Binary heap
+/// @param __topcmp Comparator
+/// @param __swp Swapper
+#define BHEAP_POP2(__heap,__topcmp,__swp) \
+	do{ \
+		VECTOR_INDEX(__heap,0) = VECTOR_POP(__heap); /* put last at index */ \
+		if( !VECTOR_LENGTH(__heap) ) /* removed last, nothing to do */ \
+			break; \
+		BHEAP_SIFTUP(__heap,0,__topcmp,__swp);	\
+	}while(0)
+
+
+
 /// Removes the target value of the heap. (using the '=' operator)
 /// Assumes the index exists.
 ///
@@ -1522,6 +1553,74 @@ void  linkdb_foreach (struct linkdb_node** head, LinkDBFunc func, ...);
 
 
 
+/// Follow path up towards (but not all the way to) the root, swapping nodes until finding
+/// a place where the new item that was placed at __idx fits.
+/// Only goes as high as __startidx (usually 0).
+///
+/// @param __heap Binary heap
+/// @param __startidx Index of an ancestor of __idx
+/// @param __idx Index of an inserted element
+/// @param __topcmp Comparator
+/// @param __swp Swapper
+#define BHEAP_SIFTDOWN(__heap,__startidx,__idx,__topcmp,__swp)	\
+	do{ \
+		size_t _i2_ = __idx; \
+		while( _i2_ > __startidx ) \
+		{ /* restore heap property in parents */ \
+			size_t _parent_ = (_i2_-1)/2; \
+			if( __topcmp(VECTOR_INDEX(__heap,_parent_),VECTOR_INDEX(__heap,_i2_)) <= 0 ) \
+				break; /* done */ \
+			__swp(VECTOR_INDEX(__heap,_parent_),VECTOR_INDEX(__heap,_i2_)); \
+			_i2_ = _parent_; \
+		} \
+	}while(0)
+
+
+
+/// Repeatedly swap the smaller child with parent, after placing a new item at __idx.
+///
+/// @param __heap Binary heap
+/// @param __idx Index of an inserted element
+/// @param __topcmp Comparator
+/// @param __swp Swapper
+#define BHEAP_SIFTUP(__heap,__idx,__topcmp,__swp) \
+	do{ \
+		size_t _i_ = __idx; \
+		size_t _lchild_ = _i_*2 + 1; \
+		while( _lchild_ < VECTOR_LENGTH(__heap) ) \
+		{ /* restore heap property in childs */ \
+			size_t _rchild_ = _i_*2 + 2; \
+			if( _rchild_ >= VECTOR_LENGTH(__heap) || __topcmp(VECTOR_INDEX(__heap,_lchild_),VECTOR_INDEX(__heap,_rchild_)) < 0 ) \
+			{ /* left child */ \
+				__swp(VECTOR_INDEX(__heap,_i_),VECTOR_INDEX(__heap,_lchild_)); \
+				_i_ = _lchild_; \
+			} \
+			else \
+			{ /* right child */ \
+				__swp(VECTOR_INDEX(__heap,_i_),VECTOR_INDEX(__heap,_rchild_)); \
+				_i_ = _rchild_; \
+			} \
+			_lchild_ = _i_*2 + 1; \
+		} \
+		BHEAP_SIFTDOWN(__heap,__idx,_i_,__topcmp,__swp); \
+	}while(0)
+
+
+
+/// Call this after modifying the item at __idx__ to restore the heap
+///
+/// @param __heap Binary heap
+/// @param __idx Index
+/// @param __topcmp Comparator
+/// @param __swp Swapper
+#define BHEAP_UPDATE(__heap,__idx,__topcmp,__swp) \
+	do{ \
+		BHEAP_SIFTDOWN(__heap,0,__idx,__topcmp,__swp); \
+		BHEAP_SIFTUP(__heap,__idx,__topcmp,__swp); \
+	}while(0)
+
+
+
 /// Clears the binary heap, freeing allocated data.
 ///
 /// @param __heap Binary heap
-- 
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