charcoal/OpenGLEngine/Batch.h

#pragma once

#include "stdafx.h"

#include <cstddef>
#include <vector>

#include "Exception.h"

namespace
{
	struct EmptyElement {};
}

template <typename VertexType, typename IndexType, typename ElementType = EmptyElement, typename RenderableType = Renderable<VertexType, IndexType> >
class Batch
{
public:
	typedef GLsizei SizeType;

	Batch(
		const RenderableType* renderable,
		const SizeType& element_count,
		const SizeType& element_render_count
	)
		: m_p_renderable(renderable), m_elements(element_count), m_element_render_count(element_render_count)
	{
		if (std::is_same<unsigned int, IndexType>::value)
		{
			m_gl_index_type = GL_UNSIGNED_INT;
		}
		else if (std::is_same<unsigned short, IndexType>::value)
		{
			m_gl_index_type = GL_UNSIGNED_SHORT;
		}
		else if (std::is_same<unsigned char, IndexType>::value)
		{
			m_gl_index_type = GL_UNSIGNED_BYTE;
		}
		else
		{
			throw EXCEPTION("Invalid Batch IndexType");
		}

		glGenVertexArrays(1, &m_vao);
		glGenBuffers(1, &m_vertex_vbo);
		glGenBuffers(1, &m_index_vbo);
	}

	virtual ~Batch()
	{
		glDeleteVertexArrays(1, &m_vao);
		glDeleteBuffers(1, &m_vertex_vbo);
		glDeleteBuffers(1, &m_index_vbo);
	}

	void init()
	{
		glBindBuffer(GL_ARRAY_BUFFER, m_vertex_vbo);
		glBufferData(GL_ARRAY_BUFFER, m_p_renderable->get_mesh()->vertex_count * sizeof(VertexType), m_p_renderable->get_mesh()->vertices, GL_STATIC_DRAW);
		glBindBuffer(GL_ARRAY_BUFFER, NULL);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_index_vbo);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, m_p_renderable->get_mesh()->index_count * sizeof(IndexType), m_p_renderable->get_mesh()->indices, GL_STATIC_DRAW);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, NULL);

		setup_element_buffer();

		glBindVertexArray(m_vao); // Possibly want to move these three lines into the init function
		glBindBuffer(GL_ARRAY_BUFFER, m_vertex_vbo);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_index_vbo);

		setup_vao();

		glBindVertexArray(NULL);
	}

	void render() const
	{
		glBindVertexArray(m_vao);
		glDrawElementsInstanced(
			m_p_renderable->get_draw_mode(),
			m_p_renderable->get_mesh()->index_count,
			m_gl_index_type,
			0,
			(GLsizei)m_element_render_count
		);
		glBindVertexArray(NULL);
	}

	void set_element_render_count(const SizeType& element_render_count)
	{
		m_element_render_count = element_render_count;
	}

	ElementType& get_element() { return m_elements[0]; }

	ElementType& get_element(const SizeType& index) { return m_elements[index]; }

	const ElementType& get_element() const { return m_elements[0]; }

	const ElementType& get_element(const SizeType& index) const { return m_elements[index]; }

protected:
	virtual void setup_element_buffer() {}

	virtual void setup_vao() = 0;

	const RenderableType* m_p_renderable;
	std::vector<ElementType> m_elements;
	SizeType m_element_render_count;

private:
	GLuint m_vao;
	GLuint m_vertex_vbo;
	GLuint m_index_vbo;
	GLenum m_gl_index_type;
};