From a4b3f04803aceb9c750d4317a3e7cf3e56996518 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 1 Apr 2024 20:07:00 +0100
Subject: Replace face 4-way split

Fixes integer rounding issue and returns the new face handles
---
 game/geoData.cpp | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 game/geoData.h   |  3 +++
 2 files changed, 59 insertions(+)

(limited to 'game')

diff --git a/game/geoData.cpp b/game/geoData.cpp
index ccad9e0..059b03d 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -396,6 +396,62 @@ GeoData::triangleContainsTriangle(const Triangle<2> & a, const Triangle<2> & b)
 	return triangleContainsPoint(a.x, b) && triangleContainsPoint(a.y, b) && triangleContainsPoint(a.z, b);
 }
 
+std::array<GeoData::FaceHandle, 4>
+GeoData::split(FaceHandle _fh)
+{
+	// Collect halfedges of face
+	const HalfedgeHandle he0 = halfedge_handle(_fh);
+	const HalfedgeHandle he1 = next_halfedge_handle(he0);
+	const HalfedgeHandle he2 = next_halfedge_handle(he1);
+
+	const EdgeHandle eh0 = edge_handle(he0);
+	const EdgeHandle eh1 = edge_handle(he1);
+	const EdgeHandle eh2 = edge_handle(he2);
+
+	// Collect points of face
+	const VertexHandle p0 = to_vertex_handle(he0);
+	const VertexHandle p1 = to_vertex_handle(he1);
+	const VertexHandle p2 = to_vertex_handle(he2);
+
+	// Calculate midpoint coordinates
+	const Point new0 = centre(he0);
+	const Point new1 = centre(he1);
+	const Point new2 = centre(he2);
+
+	// Add vertices at midpoint coordinates
+	const VertexHandle v0 = add_vertex(new0);
+	const VertexHandle v1 = add_vertex(new1);
+	const VertexHandle v2 = add_vertex(new2);
+
+	const bool split0 = !is_boundary(eh0);
+	const bool split1 = !is_boundary(eh1);
+	const bool split2 = !is_boundary(eh2);
+
+	// delete original face
+	delete_face(_fh, false);
+
+	// split boundary edges of deleted face ( if not boundary )
+	if (split0) {
+		split(eh0, v0);
+	}
+
+	if (split1) {
+		split(eh1, v1);
+	}
+
+	if (split2) {
+		split(eh2, v2);
+	}
+
+	// Retriangulate
+	return {
+			add_face(v0, p0, v1),
+			add_face(p2, v0, v2),
+			add_face(v2, v1, p1),
+			add_face(v2, v0, v1),
+	};
+}
+
 void
 GeoData::setHeights(const std::span<const GlobalPosition3D> triangleStrip)
 {
diff --git a/game/geoData.h b/game/geoData.h
index 88eb304..6dacd9a 100644
--- a/game/geoData.h
+++ b/game/geoData.h
@@ -115,6 +115,9 @@ protected:
 
 	void update_vertex_normals_only();
 
+	using OpenMesh::TriMesh_ArrayKernelT<GeoDataTraits>::split;
+	std::array<FaceHandle, 4> split(FaceHandle);
+
 private:
 	GlobalPosition3D lowerExtent {}, upperExtent {};
 };
-- 
cgit v1.2.3