From f70cbc0dade14cf07cad774ffc8f5c903b1a5ea8 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 12 Mar 2025 02:59:12 +0000
Subject: Split Terrain::generateMeshes into smaller functions

Also removes incorrect optimisation that a tile's AABB could be assumed
from tile base position; in fact some faces cross the boundaries and the
AABB needs to account for this.
---
 game/terrain.cpp | 54 +++++++++++++++++++++++++++++++++++++-----------------
 game/terrain.h   |  9 ++++++++-
 2 files changed, 45 insertions(+), 18 deletions(-)

(limited to 'game')

diff --git a/game/terrain.cpp b/game/terrain.cpp
index d3c1d1a..f10aac6 100644
--- a/game/terrain.cpp
+++ b/game/terrain.cpp
@@ -30,19 +30,26 @@ Terrain::SurfaceKey::operator<(const SurfaceKey & other) const
 			< std::tie(other.surface, other.basePosition.x, other.basePosition.y);
 }
 
-void
-Terrain::generateMeshes()
+inline void
+Terrain::copyVerticesToBuffer() const
 {
 	std::ranges::transform(all_vertices(), glMappedBufferWriter<Vertex> {GL_ARRAY_BUFFER, verticesBuffer, n_vertices()},
 			[this](const auto & vertex) {
 				return Vertex {point(vertex), normal(vertex)};
 			});
+}
 
-	std::map<SurfaceKey, std::vector<GLuint>> surfaceIndices;
-	const auto getTile = [this](FaceHandle face) {
-		return point(*fv_begin(face)).xy() / TILE_SIZE;
-	};
-	const auto indexBySurfaceAndTile = std::views::transform([this, &getTile](const auto & faceItr) {
+inline GlobalPosition2D
+Terrain::getTile(const FaceHandle & face) const
+{
+	return point(*cfv_begin(face)).xy() / TILE_SIZE;
+};
+
+Terrain::SurfaceIndices
+Terrain::mapSurfaceFacesToIndices() const
+{
+	SurfaceIndices surfaceIndices;
+	const auto indexBySurfaceAndTile = std::views::transform([this](const auto & faceItr) {
 		return std::pair<SurfaceKey, FaceHandle> {{getSurface(*faceItr), getTile(*faceItr)}, *faceItr};
 	});
 	const auto chunkBySurfaceAndTile = std::views::chunk_by([](const auto & face1, const auto & face2) {
@@ -61,7 +68,12 @@ Terrain::generateMeshes()
 			std::ranges::transform(fv_range(face), push, &OpenMesh::VertexHandle::idx);
 		}
 	}
+	return surfaceIndices;
+}
 
+void
+Terrain::copyIndicesToBuffers(const SurfaceIndices & surfaceIndices)
+{
 	for (const auto & [surfaceKey, indices] : surfaceIndices) {
 		auto meshItr = meshes.find(surfaceKey);
 		if (meshItr == meshes.end()) {
@@ -77,17 +89,16 @@ Terrain::generateMeshes()
 					.data(verticesBuffer, GL_ARRAY_BUFFER);
 		}
 		meshItr->second.count = static_cast<GLsizei>(indices.size());
-		if (!surfaceKey.surface) {
-			meshItr->second.aabb = {{surfaceKey.basePosition * TILE_SIZE || getExtents().min.z},
-					{(surfaceKey.basePosition + 1) * TILE_SIZE || getExtents().max.z}};
-		}
-		else {
-			meshItr->second.aabb = AxisAlignedBoundingBox<GlobalDistance>::fromPoints(
-					indices | std::views::transform([this](const auto vertex) -> GlobalPosition3D {
-						return this->point(VertexHandle {static_cast<int>(vertex)});
-					}));
-		}
+		meshItr->second.aabb = AxisAlignedBoundingBox<GlobalDistance>::fromPoints(
+				indices | std::views::transform([this](const auto vertex) {
+					return this->point(VertexHandle {static_cast<int>(vertex)});
+				}));
 	}
+}
+
+void
+Terrain::pruneOrphanMeshes(const SurfaceIndices & surfaceIndices)
+{
 	if (meshes.size() > surfaceIndices.size()) {
 		std::erase_if(meshes, [&surfaceIndices](const auto & mesh) {
 			return !surfaceIndices.contains(mesh.first);
@@ -95,6 +106,15 @@ Terrain::generateMeshes()
 	}
 }
 
+void
+Terrain::generateMeshes()
+{
+	copyVerticesToBuffer();
+	const auto surfaceIndices = mapSurfaceFacesToIndices();
+	copyIndicesToBuffers(surfaceIndices);
+	pruneOrphanMeshes(surfaceIndices);
+}
+
 void
 Terrain::tick(TickDuration)
 {
diff --git a/game/terrain.h b/game/terrain.h
index eaec01d..1a63296 100644
--- a/game/terrain.h
+++ b/game/terrain.h
@@ -41,9 +41,16 @@ private:
 	struct SurfaceKey {
 		const Surface * surface;
 		GlobalPosition2D basePosition;
-		bool operator<(const SurfaceKey &) const;
+		inline bool operator<(const SurfaceKey &) const;
 	};
 
+	using SurfaceIndices = std::map<SurfaceKey, std::vector<GLuint>>;
+	void copyVerticesToBuffer() const;
+	[[nodiscard]] SurfaceIndices mapSurfaceFacesToIndices() const;
+	void copyIndicesToBuffers(const SurfaceIndices &);
+	void pruneOrphanMeshes(const SurfaceIndices &);
+	[[nodiscard]] inline GlobalPosition2D getTile(const FaceHandle &) const;
+
 	glBuffer verticesBuffer;
 	std::map<SurfaceKey, SurfaceArrayBuffer> meshes;
 	Texture::Ptr grass = std::make_shared<Texture>("grass.png");
-- 
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