From 666f4603ee94148e41b4433a7f7a02d2f79d4651 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Thu, 4 Apr 2024 19:57:41 +0100
Subject: Update normals only as required

---
 game/geoData.cpp | 22 ++++++++++++++++------
 game/geoData.h   |  1 +
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/game/geoData.cpp b/game/geoData.cpp
index 1d11fda..9211369 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -373,11 +373,19 @@ GeoData::centre(const HalfedgeHandle heh) const
 void
 GeoData::update_vertex_normals_only()
 {
-	for (auto vh : all_vertices()) {
-		Normal3D n;
-		calc_vertex_normal_correct(vh, n);
-		this->set_normal(vh, glm::normalize(n));
-	}
+	update_vertex_normals_only(vertices_sbegin());
+}
+
+void
+GeoData::update_vertex_normals_only(VertexIter start)
+{
+	std::for_each(start, vertices_end(), [this](const auto vh) {
+		if (normal(vh) == Normal3D {}) {
+			Normal3D n;
+			calc_vertex_normal_correct(vh, n);
+			this->set_normal(vh, glm::normalize(n));
+		}
+	});
 }
 
 bool
@@ -462,6 +470,8 @@ GeoData::setHeights(const std::span<const GlobalPosition3D> triangleStrip)
 		return;
 	}
 
+	const auto initialVertexCount = static_cast<unsigned int>(n_vertices());
+
 	// Create new vertices
 	std::vector<VertexHandle> newVerts;
 	newVerts.reserve(newVerts.size());
@@ -653,6 +663,6 @@ GeoData::setHeights(const std::span<const GlobalPosition3D> triangleStrip)
 	});
 
 	// Tidy up
+	update_vertex_normals_only(VertexIter {*this, vertex_handle(initialVertexCount), true});
 	garbage_collection();
-	update_vertex_normals_only();
 }
diff --git a/game/geoData.h b/game/geoData.h
index 03bc159..021b4c7 100644
--- a/game/geoData.h
+++ b/game/geoData.h
@@ -180,6 +180,7 @@ protected:
 	[[nodiscard]] GlobalPosition3D centre(const HalfedgeHandle) const;
 
 	void update_vertex_normals_only();
+	void update_vertex_normals_only(VertexIter start);
 
 	using OpenMesh::TriMesh_ArrayKernelT<GeoDataTraits>::split;
 	std::array<FaceHandle, 4> split(FaceHandle);
-- 
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