From ef00fc9ae1323b64d5e167d04a987887c60c6ec0 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 10 May 2023 00:02:50 +0100
Subject: Make Mesh into a template to support any vertex type

Customisation point VertexArrayObject to define the layout for the type
---
 gfx/gl/vertexArrayObject.h |  3 +++
 gfx/models/mesh.cpp        | 22 +++-------------------
 gfx/models/mesh.h          | 30 ++++++++++++++++++++++++------
 gfx/models/vertex.cpp      | 10 ++++++++++
 4 files changed, 40 insertions(+), 25 deletions(-)
 create mode 100644 gfx/models/vertex.cpp

diff --git a/gfx/gl/vertexArrayObject.h b/gfx/gl/vertexArrayObject.h
index 085cba6..1d27588 100644
--- a/gfx/gl/vertexArrayObject.h
+++ b/gfx/gl/vertexArrayObject.h
@@ -46,6 +46,9 @@ public:
 		return *this;
 	}
 
+	// Customisation point
+	template<typename VertexT> VertexArrayObject & addAttribsFor(const GLuint arrayBuffer, const GLuint divisor = 0);
+
 	template<typename Indices>
 	VertexArrayObject &
 	addIndices(const GLuint arrayBuffer, const Indices & indices)
diff --git a/gfx/models/mesh.cpp b/gfx/models/mesh.cpp
index a1ce991..1f4dc09 100644
--- a/gfx/models/mesh.cpp
+++ b/gfx/models/mesh.cpp
@@ -1,28 +1,12 @@
 #include "mesh.h"
-#include "gfx/gl/vertexArrayObject.h"
 #include "glArrays.h"
 #include "vertex.h"
 #include <cstddef>
 
-Mesh::Mesh(const std::span<const Vertex> vertices, const std::span<const unsigned int> indices, GLenum m) :
-	m_numIndices {static_cast<GLsizei>(indices.size())}, mode {m}
-{
-	VertexArrayObject::data(vertices, m_vertexArrayBuffers[0], GL_ARRAY_BUFFER);
-	VertexArrayObject::data(indices, m_vertexArrayBuffers[1], GL_ARRAY_BUFFER);
-	configureVAO(m_vertexArrayObject);
-}
-
-VertexArrayObject &
-Mesh::configureVAO(VertexArrayObject && vao) const
-{
-	return vao
-			.addAttribs<Vertex, &Vertex::pos, &Vertex::texCoord, &Vertex::normal, &Vertex::colour, &Vertex::material>(
-					m_vertexArrayBuffers[0])
-			.addIndices(m_vertexArrayBuffers[1]);
-}
+MeshBase::MeshBase(GLsizei m_numIndices, GLenum mode) : m_numIndices {m_numIndices}, mode {mode} { }
 
 void
-Mesh::Draw() const
+MeshBase::Draw() const
 {
 	glBindVertexArray(m_vertexArrayObject);
 
@@ -32,7 +16,7 @@ Mesh::Draw() const
 }
 
 void
-Mesh::DrawInstanced(GLuint vao, GLsizei count) const
+MeshBase::DrawInstanced(GLuint vao, GLsizei count) const
 {
 	glBindVertexArray(vao);
 
diff --git a/gfx/models/mesh.h b/gfx/models/mesh.h
index f022c2a..972fe30 100644
--- a/gfx/models/mesh.h
+++ b/gfx/models/mesh.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "gfx/gl/vertexArrayObject.h"
 #include <GL/glew.h>
 #include <glArrays.h>
 #include <memory>
@@ -7,19 +8,36 @@
 #include <stdTypeDefs.h>
 
 class Vertex;
-class VertexArrayObject;
 
-class Mesh : public ConstTypeDefs<Mesh> {
+class MeshBase {
 public:
-	Mesh(const std::span<const Vertex> vertices, const std::span<const unsigned int> indices, GLenum = GL_TRIANGLES);
-
 	void Draw() const;
 	void DrawInstanced(GLuint vao, GLsizei count) const;
-	VertexArrayObject & configureVAO(VertexArrayObject &&) const;
 
-private:
+protected:
+	MeshBase(GLsizei m_numIndices, GLenum mode);
+
 	glVertexArray m_vertexArrayObject;
 	glBuffers<2> m_vertexArrayBuffers;
 	GLsizei m_numIndices;
 	GLenum mode;
 };
+
+template<typename V> class MeshT : public MeshBase, public ConstTypeDefs<MeshT<V>> {
+public:
+	MeshT(const std::span<const V> vertices, const std::span<const unsigned int> indices, GLenum mode = GL_TRIANGLES) :
+		MeshBase {static_cast<GLsizei>(indices.size()), mode}
+	{
+		VertexArrayObject::data(vertices, m_vertexArrayBuffers[0], GL_ARRAY_BUFFER);
+		VertexArrayObject::data(indices, m_vertexArrayBuffers[1], GL_ARRAY_BUFFER);
+		configureVAO(m_vertexArrayObject);
+	}
+
+	VertexArrayObject &
+	configureVAO(VertexArrayObject && vao) const
+	{
+		return vao.addAttribsFor<V>(m_vertexArrayBuffers[0]).addIndices(m_vertexArrayBuffers[1]);
+	}
+};
+
+using Mesh = MeshT<Vertex>;
diff --git a/gfx/models/vertex.cpp b/gfx/models/vertex.cpp
new file mode 100644
index 0000000..c144db3
--- /dev/null
+++ b/gfx/models/vertex.cpp
@@ -0,0 +1,10 @@
+#include "vertex.h"
+#include "gfx/gl/vertexArrayObject.h"
+
+template<>
+VertexArrayObject &
+VertexArrayObject::addAttribsFor<Vertex>(const GLuint arrayBuffer, const GLuint divisor)
+{
+	return addAttribs<Vertex, &Vertex::pos, &Vertex::texCoord, &Vertex::normal, &Vertex::colour, &Vertex::material>(
+			arrayBuffer, divisor);
+}
-- 
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