From 2f9776d495f6a5c7bedccc3566b81d41d28e09f6 Mon Sep 17 00:00:00 2001
From: Kawe Mazidjatari <48657826+Mauler125@users.noreply.github.com>
Date: Fri, 12 Jul 2024 21:38:50 +0200
Subject: [PATCH] Recast: properly set dtPoly::surfaceArea

This field has been reverse engineered and set correctly in this commit. The field contains the quantized surface area of the polygon.
---
 .../recast/Detour/Include/DetourNavMesh.h       | 15 +++++++++++++--
 .../recast/Detour/Source/DetourNavMesh.cpp      | 17 +++++++++++++++++
 .../Detour/Source/DetourNavMeshBuilder.cpp      |  3 ++-
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/src/thirdparty/recast/Detour/Include/DetourNavMesh.h b/src/thirdparty/recast/Detour/Include/DetourNavMesh.h
index 0f45e65d..f46c5317 100644
--- a/src/thirdparty/recast/Detour/Include/DetourNavMesh.h
+++ b/src/thirdparty/recast/Detour/Include/DetourNavMesh.h
@@ -82,6 +82,9 @@ static const int DT_MIN_POLY_GROUP_COUNT = 3;
 /// The maximum number of traversal tables per navmesh that will be used for static pathing.
 static const int DT_MAX_TRAVERSAL_TABLES = 5;
 
+/// The cached poly surface area quantization factor.
+static const float DT_POLY_AREA_QUANT_FACTOR = 50.f;
+
 /// @{
 /// @name Tile Serialization Constants
 /// These constants are used to detect whether a navigation tile's data
@@ -205,11 +208,13 @@ struct dtPoly
 	/// The poly group id determining to which island it belongs, and to which it connects.
 	unsigned short groupId;
 
-	// These 3 are most likely related, it needs to be reversed still.
+	/// The poly surface area. (Quantized by #DT_POLY_AREA_QUANT_FACTOR).
+	unsigned short surfaceArea;
+
+	// These 2 are most likely related, it needs to be reversed still.
 	// No use case has been found in the executable yet, its possible these are
 	// used internally in the editor. Dynamic reverse engineering required to
 	// confirm this.
-	unsigned short unk0;
 	unsigned short unk1;
 	unsigned short unk2;
 
@@ -229,6 +234,12 @@ struct dtPoly
 	inline unsigned char getType() const { return areaAndtype >> 6; }
 };
 
+/// Calculates the surface area of the polygon.
+///  @param[in]		poly	The polygon.
+///  @param[in]		verts	The polygon vertices.
+/// @return The total surface are of the polygon.
+float dtCalcPolySurfaceArea(const dtPoly* poly, const float* verts);
+
 /// Defines the location of detail sub-mesh data within a dtMeshTile.
 struct dtPolyDetail
 {
diff --git a/src/thirdparty/recast/Detour/Source/DetourNavMesh.cpp b/src/thirdparty/recast/Detour/Source/DetourNavMesh.cpp
index cbac26dc..962c760c 100644
--- a/src/thirdparty/recast/Detour/Source/DetourNavMesh.cpp
+++ b/src/thirdparty/recast/Detour/Source/DetourNavMesh.cpp
@@ -1695,6 +1695,23 @@ dtStatus dtNavMesh::getPolyArea(dtPolyRef ref, unsigned char* resultArea) const
 	return DT_SUCCESS;
 }
 
+float dtCalcPolyArea(const dtPoly* poly, const float* verts)
+{
+	float polyArea = 0.0f;
+
+	// Only run if we have more than 2 verts since poly's with 2 verts
+	// (off-mesh connections) don't have any surface area.
+	for (int j = 2; j < poly->vertCount; ++j)
+	{
+		const float* va = &verts[poly->verts[0]*3];
+		const float* vb = &verts[poly->verts[j]*3];
+		const float* vc = &verts[poly->verts[j-1]*3];
+		polyArea += dtTriArea2D(va,vb,vc);
+	}
+
+	return polyArea;
+}
+
 float dtCalcOffMeshRefYaw(const float* spos, const float* epos)
 {
 	float dx = epos[0]-spos[0];
diff --git a/src/thirdparty/recast/Detour/Source/DetourNavMeshBuilder.cpp b/src/thirdparty/recast/Detour/Source/DetourNavMeshBuilder.cpp
index cfe8389d..ca91197c 100644
--- a/src/thirdparty/recast/Detour/Source/DetourNavMeshBuilder.cpp
+++ b/src/thirdparty/recast/Detour/Source/DetourNavMeshBuilder.cpp
@@ -303,7 +303,6 @@ bool dtCreateDisjointPolyGroups(dtNavMesh* nav, dtDisjointSet& disjoint)
 
 			// NOTE: these fields are unknown and need to be reversed.
 			// It is possible these are used internally only.
-			poly.unk0 = (unsigned short)-1;
 			poly.unk1 = (unsigned short)-1;
 			poly.unk2 = (unsigned short)-1;
 		}
@@ -815,6 +814,8 @@ bool dtCreateNavMeshData(dtNavMeshCreateParams* params, unsigned char** outData,
 			p->vertCount++;
 		}
 		dtVscale(p->center, p->center, 1 / (float)(p->vertCount));
+		p->surfaceArea = (unsigned short)dtMathRoundf(dtCalcPolySurfaceArea(p,navVerts) / DT_POLY_AREA_QUANT_FACTOR);
+
 		src += nvp*2;
 	}
 	// Off-mesh connection vertices.