From 07f478ba964464ff6a6f6bc6855acc8353b4594b Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 2 Jan 2023 15:10:27 +0000
Subject: Add helper for configuring vertex array objects/buffers of arbitrary
 things

---
 gfx/gl/vertexArrayObject.hpp | 76 ++++++++++++++++++++++++++++++++++++++++++++
 gfx/models/mesh.cpp          | 27 +++-------------
 2 files changed, 80 insertions(+), 23 deletions(-)
 create mode 100644 gfx/gl/vertexArrayObject.hpp

diff --git a/gfx/gl/vertexArrayObject.hpp b/gfx/gl/vertexArrayObject.hpp
new file mode 100644
index 0000000..d90cc59
--- /dev/null
+++ b/gfx/gl/vertexArrayObject.hpp
@@ -0,0 +1,76 @@
+#pragma once
+
+#include "collections.hpp"
+#include "gl_traits.hpp"
+#include <GL/glew.h>
+#include <glm/common.hpp>
+
+template<typename Vertex> class VertexArrayObject {
+public:
+	template<auto Vertex::*... attribs>
+	static void
+	configure(const GLuint arrayObject, const GLuint arrayBuffer, const GLuint indexBuffer,
+			const SequentialCollection<Vertex> auto & vertices, const SequentialCollection<unsigned int> auto & indices)
+	{
+		glBindVertexArray(arrayObject);
+
+		configure_attribs<attribs...>(arrayBuffer);
+		data(vertices, arrayBuffer, GL_ARRAY_BUFFER);
+		data(indices, indexBuffer, GL_ELEMENT_ARRAY_BUFFER);
+
+		glBindVertexArray(0);
+	}
+
+	template<auto Vertex::*... attribs>
+	static void
+	configure(const GLuint arrayObject, const GLuint arrayBuffer, const SequentialCollection<Vertex> auto & vertices)
+	{
+		glBindVertexArray(arrayObject);
+
+		configure_attribs<attribs...>(arrayBuffer);
+		data(vertices, arrayBuffer, GL_ARRAY_BUFFER);
+
+		glBindVertexArray(0);
+	}
+
+	template<auto Vertex::*... attribs>
+	static void
+	configure(const GLuint arrayObject, const GLuint arrayBuffer)
+	{
+		glBindVertexArray(arrayObject);
+
+		configure_attribs<attribs...>(arrayBuffer);
+		glBufferData(GL_ARRAY_BUFFER, static_cast<GLsizeiptr>(sizeof(Vertex)), nullptr, GL_DYNAMIC_DRAW);
+
+		glBindVertexArray(0);
+	}
+
+private:
+	template<typename Data>
+	static void
+	data(const Data & data, const GLuint arrayBuffer, GLenum target)
+	{
+		using Value = typename Data::element_type;
+		glBindBuffer(target, arrayBuffer);
+		glBufferData(target, static_cast<GLsizeiptr>(sizeof(Value) * data.size()), data.data(), GL_STATIC_DRAW);
+	}
+
+	template<auto Vertex::*attrib>
+	static void
+	set_pointer(GLuint & vertexArrayId)
+	{
+		glEnableVertexAttribArray(vertexArrayId);
+		using traits = gl_traits<std::decay_t<decltype(std::declval<Vertex>().*attrib)>>;
+		glVertexAttribPointer(vertexArrayId++, traits::size, traits::type, GL_FALSE, sizeof(Vertex),
+				&(static_cast<const Vertex *>(nullptr)->*attrib));
+	}
+
+	template<auto Vertex::*... attribs>
+	static void
+	configure_attribs(const GLuint arrayBuffer)
+	{
+		glBindBuffer(GL_ARRAY_BUFFER, arrayBuffer);
+		GLuint vertexArrayId {};
+		(set_pointer<attribs>(vertexArrayId), ...);
+	}
+};
diff --git a/gfx/models/mesh.cpp b/gfx/models/mesh.cpp
index f13e242..85be84c 100644
--- a/gfx/models/mesh.cpp
+++ b/gfx/models/mesh.cpp
@@ -1,33 +1,14 @@
 #include "mesh.h"
+#include "gfx/gl/vertexArrayObject.hpp"
 #include "glArrays.h"
 #include "vertex.hpp"
 #include <cstddef>
 
-#define offset_ptr(T, m) ((reinterpret_cast<char *>(1)) + offsetof(T, m) - 1)
-
 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}
 {
-	glBindVertexArray(m_vertexArrayObject);
-
-	glBindBuffer(GL_ARRAY_BUFFER, m_vertexArrayBuffers[0]);
-	glBufferData(GL_ARRAY_BUFFER, static_cast<GLsizeiptr>(sizeof(Vertex) * vertices.size()), vertices.data(),
-			GL_STATIC_DRAW);
-
-	glEnableVertexAttribArray(0);
-	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), offset_ptr(Vertex, pos));
-
-	glEnableVertexAttribArray(1);
-	glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), offset_ptr(Vertex, texCoord));
-
-	glEnableVertexAttribArray(2);
-	glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), offset_ptr(Vertex, normal));
-
-	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_vertexArrayBuffers[1]);
-	glBufferData(GL_ELEMENT_ARRAY_BUFFER, static_cast<GLsizeiptr>(sizeof(indices[0]) * indices.size()), indices.data(),
-			GL_STATIC_DRAW);
-
-	glBindVertexArray(0);
+	VertexArrayObject<Vertex>::configure<&Vertex::pos, &Vertex::texCoord, &Vertex::normal>(
+			m_vertexArrayObject, m_vertexArrayBuffers[0], m_vertexArrayBuffers[1], vertices, indices);
 }
 
 void
@@ -35,7 +16,7 @@ Mesh::Draw() const
 {
 	glBindVertexArray(m_vertexArrayObject);
 
-	glDrawElementsBaseVertex(mode, m_numIndices, GL_UNSIGNED_INT, nullptr, 0);
+	glDrawElements(mode, m_numIndices, GL_UNSIGNED_INT, nullptr);
 
 	glBindVertexArray(0);
 }
-- 
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