From f9962b0db5072870864a1f758687106139f740dc Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Tue, 25 Feb 2025 00:23:11 +0000
Subject: Improve Terrain::generateMeshes performance

Creates mesh per surface based on a single buffer of all vertices and a collection of per surfuce indices.
Makes ColourBias a uniform instead of a vertex attribute.
---
 game/terrain.cpp | 79 +++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 50 insertions(+), 29 deletions(-)

(limited to 'game/terrain.cpp')

diff --git a/game/terrain.cpp b/game/terrain.cpp
index 01af163..c28f7ee 100644
--- a/game/terrain.cpp
+++ b/game/terrain.cpp
@@ -1,12 +1,11 @@
 #include "terrain.h"
-#include "game/geoData.h"
 #include <algorithm>
-#include <cstddef>
 #include <gfx/gl/sceneShader.h>
 #include <gfx/gl/shadowMapper.h>
 #include <gfx/image.h>
 #include <gfx/models/mesh.h>
 #include <gfx/models/vertex.h>
+#include <glMappedBufferWriter.h>
 #include <glm/glm.hpp>
 #include <iterator>
 #include <location.h>
@@ -20,37 +19,51 @@ template<>
 VertexArrayObject &
 VertexArrayObject::addAttribsFor<Terrain::Vertex>(const GLuint arrayBuffer, const GLuint divisor)
 {
-	return addAttribs<Terrain::Vertex, &Terrain::Vertex::pos, &Terrain::Vertex::normal, &Terrain::Vertex::colourBias>(
-			arrayBuffer, divisor);
+	return addAttribs<Terrain::Vertex, &Terrain::Vertex::pos, &Terrain::Vertex::normal>(arrayBuffer, divisor);
 }
 
 void
 Terrain::generateMeshes()
 {
-	meshes.removeAll();
-	std::vector<unsigned int> indices;
-	indices.reserve(n_faces() * 3);
-	std::vector<Vertex> vertices;
-	vertices.reserve(n_vertices());
-	std::map<std::pair<VertexHandle, const Surface *>, size_t> vertexIndex;
-	std::ranges::for_each(this->vertices(), [this, &vertexIndex, &vertices](const auto vertex) {
-		std::ranges::for_each(vf_range(vertex), [&vertexIndex, vertex, this, &vertices](const auto face) {
-			const auto * const surface = getSurface(face);
-			if (const auto vertexIndexRef = vertexIndex.emplace(std::make_pair(vertex, surface), 0);
-					vertexIndexRef.second) {
-				vertexIndexRef.first->second = vertices.size();
+	std::ranges::transform(all_vertices(), glMappedBufferWriter<Vertex> {GL_ARRAY_BUFFER, verticesBuffer, n_vertices()},
+			[this](const auto & vertex) {
+				return Vertex {point(vertex), normal(vertex)};
+			});
 
-				vertices.emplace_back(point(vertex), normal(vertex), surface ? surface->colorBias : OPEN_SURFACE);
+	std::map<const Surface *, std::vector<GLuint>> surfaceIndices;
+	for (const auto face : faces()) {
+		const auto * const surface = getSurface(face);
+		auto indexItr = surfaceIndices.find(surface);
+		if (indexItr == surfaceIndices.end()) {
+			indexItr = surfaceIndices.emplace(surface, std::vector<GLuint> {}).first;
+			if (!surface) {
+				indexItr->second.reserve(n_vertices() * 3);
 			}
+		}
+		std::ranges::transform(fv_range(face), std::back_inserter(indexItr->second), &OpenMesh::VertexHandle::idx);
+	}
+
+	for (const auto & [surface, indices] : surfaceIndices) {
+		auto meshItr = meshes.find(surface);
+		if (meshItr == meshes.end()) {
+			meshItr = meshes.emplace(surface, SurfaceArrayBuffer {});
+			VertexArrayObject {meshItr->second.vertexArray}
+					.addAttribsFor<Vertex>(verticesBuffer)
+					.addIndices(meshItr->second.indicesBuffer, indices)
+					.data(verticesBuffer, GL_ARRAY_BUFFER);
+		}
+		else {
+			VertexArrayObject {meshItr->second.vertexArray}
+					.addIndices(meshItr->second.indicesBuffer, indices)
+					.data(verticesBuffer, GL_ARRAY_BUFFER);
+		}
+		meshItr->second.count = static_cast<GLsizei>(indices.size());
+	}
+	if (meshes.size() > surfaceIndices.size()) {
+		std::erase_if(meshes, [&surfaceIndices](const auto & mesh) {
+			return !surfaceIndices.contains(mesh.first);
 		});
-	});
-	std::ranges::for_each(faces(), [this, &vertexIndex, &indices](const auto face) {
-		std::ranges::transform(
-				fv_range(face), std::back_inserter(indices), [&vertexIndex, face, this](const auto vertex) {
-					return vertexIndex[std::make_pair(vertex, getSurface(face))];
-				});
-	});
-	meshes.create<MeshT<Vertex>>(vertices, indices);
+	}
 }
 
 void
@@ -61,20 +74,28 @@ Terrain::tick(TickDuration)
 void
 Terrain::afterChange()
 {
-		generateMeshes();
+	generateMeshes();
 }
 
 void
 Terrain::render(const SceneShader & shader) const
 {
-	shader.landmass.use();
 	grass->bind();
-	meshes.apply(&Mesh::Draw);
+	for (const auto & [surface, sab] : meshes) {
+		shader.landmass.use(surface ? surface->colorBias : OPEN_SURFACE);
+		glBindVertexArray(sab.vertexArray);
+		glDrawElements(GL_TRIANGLES, sab.count, GL_UNSIGNED_INT, nullptr);
+	}
+	glBindVertexArray(0);
 }
 
 void
 Terrain::shadows(const ShadowMapper & shadowMapper) const
 {
 	shadowMapper.landmess.use();
-	meshes.apply(&Mesh::Draw);
+	for (const auto & [surface, sab] : meshes) {
+		glBindVertexArray(sab.vertexArray);
+		glDrawElements(GL_TRIANGLES, sab.count, GL_UNSIGNED_INT, nullptr);
+	}
+	glBindVertexArray(0);
 }
-- 
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