From c403a71564def731f4d3b80d6ff63f08aa3c7ea3 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 11 Mar 2026 20:45:05 +0000
Subject: Reuse vertex array objects for common structures with DSA

Slashes the number of VAOs required and the amount of setup required.
---
 gfx/models/mesh.cpp | 11 ++++++++---
 gfx/models/mesh.h   | 26 ++++++++++++++++++++------
 2 files changed, 28 insertions(+), 9 deletions(-)

(limited to 'gfx/models')

diff --git a/gfx/models/mesh.cpp b/gfx/models/mesh.cpp
index 88314ae..6a53f52 100644
--- a/gfx/models/mesh.cpp
+++ b/gfx/models/mesh.cpp
@@ -1,7 +1,8 @@
 #include "mesh.h"
 
-MeshBase::MeshBase(GLsizei m_numIndices, GLenum mode, const std::vector<RelativePosition3D> & positions) :
-	numIndices {m_numIndices}, mode {mode}, dimensions {positions}
+MeshBase::MeshBase(
+		GLsizei m_numIndices, GLenum mode, const std::vector<RelativePosition3D> & positions, GLsizei vertexStride) :
+	vertexStride {vertexStride}, numIndices {m_numIndices}, mode {mode}, dimensions {positions}
 {
 }
 
@@ -31,7 +32,9 @@ MeshBase::Dimensions::extents(const std::span<const RelativePosition3D> position
 void
 MeshBase::draw() const
 {
-	glBindVertexArray(vertexArrayObject);
+	glBindVertexArray(*vertexArrayObject);
+	glVertexArrayVertexBuffer(*vertexArrayObject, 0, vertexArrayBuffers[0], 0, vertexStride);
+	glVertexArrayElementBuffer(*vertexArrayObject, vertexArrayBuffers[1]);
 
 	glDrawElements(mode, numIndices, GL_UNSIGNED_INT, nullptr);
 
@@ -42,6 +45,8 @@ void
 MeshBase::drawInstanced(GLuint vao, GLsizei count, GLuint base) const
 {
 	glBindVertexArray(vao);
+	glVertexArrayVertexBuffer(vao, 0, vertexArrayBuffers[0], 0, vertexStride);
+	glVertexArrayElementBuffer(vao, vertexArrayBuffers[1]);
 
 	glDrawElementsInstancedBaseInstance(mode, numIndices, GL_UNSIGNED_INT, nullptr, count, base);
 
diff --git a/gfx/models/mesh.h b/gfx/models/mesh.h
index d4dbd68..fa12ae8 100644
--- a/gfx/models/mesh.h
+++ b/gfx/models/mesh.h
@@ -2,13 +2,15 @@
 
 #include "config/types.h"
 #include "gfx/gl/glBuffer.h"
-#include "gfx/models/vertex.h"
+#include "gfx/gl/gldebug.h"
 #include <gfx/gl/glVertexArray.h>
 #include <glad/gl.h>
 #include <ranges>
 #include <span>
 #include <stdTypeDefs.h>
 
+class Vertex;
+
 class MeshBase {
 public:
 	class Dimensions {
@@ -35,10 +37,11 @@ public:
 	}
 
 protected:
-	MeshBase(GLsizei numIndices, GLenum mode, const std::vector<RelativePosition3D> &);
+	MeshBase(GLsizei numIndices, GLenum mode, const std::vector<RelativePosition3D> &, GLsizei vertexStride);
 
-	glVertexArray vertexArrayObject;
+	std::shared_ptr<glVertexArray> vertexArrayObject;
 	glBuffers<2> vertexArrayBuffers;
+	GLsizei vertexStride;
 	GLsizei numIndices;
 	GLenum mode;
 	Dimensions dimensions;
@@ -50,18 +53,29 @@ public:
 		MeshBase {static_cast<GLsizei>(indices.size()), mode,
 				materializeRange(vertices | std::views::transform([](const auto & vertex) {
 					return static_cast<RelativePosition3D>(vertex.pos);
-				}))}
+				})),
+				sizeof(V)}
 	{
+		glDebugScope _ {0};
 		vertexArrayBuffers[0].storage(vertices, 0);
 		vertexArrayBuffers[1].storage(indices, 0);
-		configureVAO(vertexArrayObject, 0);
+		if (!(vertexArrayObject = commonVertexArrayObject.lock())) {
+			commonVertexArrayObject = vertexArrayObject = std::make_shared<glVertexArray>();
+			configureVAO(*vertexArrayObject, 0);
+		}
 	}
 
 	auto
 	configureVAO(glVertexArray & vao, GLuint divisor) const
 	{
-		return vao.configure().addAttribsFor<V>(divisor, vertexArrayBuffers[0]).addIndices(vertexArrayBuffers[1]);
+		glDebugScope _ {0};
+		return vao.configure().addAttribsFor<V>(divisor);
 	}
+
+protected:
+	static std::weak_ptr<glVertexArray> commonVertexArrayObject;
 };
 
+template<typename T> std::weak_ptr<glVertexArray> MeshT<T>::commonVertexArrayObject;
+
 using Mesh = MeshT<Vertex>;
-- 
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