Mesh.hpp

#pragma once

/*
 * In this code, "Mesh" is a range of vertices that should be sent through
 *  the OpenGL pipeline together.
 * A "MeshBuffer" holds a collection of such meshes (loaded from a file) in
 *  a single OpenGL array buffer. Individual meshes can be looked up by name
 *  using the MeshBuffer::lookup() function.
 *
 */

#include "GL.hpp"
#include <glm/glm.hpp>
#include <map>
#include <limits>
#include <string>


struct Mesh {
	//Meshes are vertex ranges (and primitive types) in their MeshBuffer:

	GLenum type = GL_TRIANGLES; //type of primitives in mesh
	GLuint start = 0; //index of first vertex
	GLuint count = 0; //count of vertices

	//Bounding box.
	//useful for debug visualization and (perhaps, eventually) collision detection:
	glm::vec3 min = glm::vec3( std::numeric_limits< float >::infinity());
	glm::vec3 max = glm::vec3(-std::numeric_limits< float >::infinity());
};

struct MeshBuffer {
	//construct from a file:
	// note: will throw if file fails to read.
	MeshBuffer(std::string const &filename);

	//look up a particular mesh by name:
	// note: will throw if mesh not found.
	const Mesh &lookup(std::string const &name) const;
	
	//build a vertex array object that links this vbo to attributes to a program:
	// note: will throw if program defines attributes not contained in this buffer
	GLuint make_vao_for_program(GLuint program) const;

	//This is the OpenGL vertex buffer object containing the mesh data:
	GLuint buffer = 0;

	//-- internals ---

	//used by the lookup() function:
	std::map< std::string, Mesh > meshes;

	//These 'Attrib' structures describe the location of various attributes within the buffer (in exactly format wanted by glVertexAttribPointer). They are set when the file is loaded and are used by the "make_vao_for_program" call:
	struct Attrib {
		GLint size = 0;
		GLenum type = 0;
		GLboolean normalized = GL_FALSE;
		GLsizei stride = 0;
		GLsizei offset = 0;

		Attrib() = default;
		Attrib(GLint size_, GLenum type_, GLboolean normalized_, GLsizei stride_, GLsizei offset_)
		: size(size_), type(type_), normalized(normalized_), stride(stride_), offset(offset_) { }
	};

	Attrib Position;
	Attrib Normal;
	Attrib Color;
	Attrib TexCoord;
};