Model.h

#pragma once
#include "../Mesh.h"

GLint TextureFromFile(const char* path, string directory);


class Model
{
public:
	/*  Functions   */
	Model(GLchar* path)
	{
		this->loadModel(path);
	}
	void Draw(Shader shader);
private:
	/*  Model Data  */
	vector<Mesh> meshes;
	string directory;
	vector<Texture> textures_loaded;
	/*  Functions   */
	void loadModel(string path);
	void processNode(aiNode* node, const aiScene* scene);
	Mesh processMesh(aiMesh* mesh, const aiScene* scene);
	vector<Texture> loadMaterialTextures(aiMaterial* mat, aiTextureType type,
		string typeName);
};

void Model::Draw(Shader shader)
{
	for (GLuint i = 0; i < this->meshes.size(); i++)
		this->meshes[i].Draw(shader);
}

void Model::loadModel(string path)
{
	Assimp::Importer import;
	const aiScene* scene = import.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs);

	if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode)
	{
		cout << "ERROR::ASSIMP::" << import.GetErrorString() << endl;
		return;
	}
	this->directory = path.substr(0, path.find_last_of('/'));

	this->processNode(scene->mRootNode, scene);
}

void Model::processNode(aiNode* node, const aiScene* scene)
{
	// Process all the node's meshes (if any)
	for (GLuint i = 0; i < node->mNumMeshes; i++)
	{
		aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
		this->meshes.push_back(this->processMesh(mesh, scene));
	}
	// Then do the same for each of its children
	for (GLuint i = 0; i < node->mNumChildren; i++)
	{
		this->processNode(node->mChildren[i], scene);
	}
}

Mesh Model::processMesh(aiMesh* mesh, const aiScene* scene)
{
	// Data to fill
	vector<Vertex> vertices;
	vector<GLuint> indices;
	vector<Texture> textures;

	// Walk through each of the mesh's vertices
	for (GLuint i = 0; i < mesh->mNumVertices; i++)
	{
		Vertex vertex;
		glm::vec3 vector; // We declare a placeholder vector since assimp uses its own vector class that doesn't directly convert to glm's vec3 class so we transfer the data to this placeholder glm::vec3 first.
						  // Positions
		vector.x = mesh->mVertices[i].x;
		vector.y = mesh->mVertices[i].y;
		vector.z = mesh->mVertices[i].z;
		vertex.Position = vector;
		// Normals
		vector.x = mesh->mNormals[i].x;
		vector.y = mesh->mNormals[i].y;
		vector.z = mesh->mNormals[i].z;
		vertex.Normal = vector;
		// Texture Coordinates
		if (mesh->mTextureCoords[0]) // Does the mesh contain texture coordinates?
		{
			glm::vec2 vec;
			// A vertex can contain up to 8 different texture coordinates. We thus make the assumption that we won't 
			// use models where a vertex can have multiple texture coordinates so we always take the first set (0).
			vec.x = mesh->mTextureCoords[0][i].x;
			vec.y = mesh->mTextureCoords[0][i].y;
			vertex.TexCoords = vec;
		}
		else
			vertex.TexCoords = glm::vec2(0.0f, 0.0f);
		vertices.push_back(vertex);
	}
	// Now wak through each of the mesh's faces (a face is a mesh its triangle) and retrieve the corresponding vertex indices.
	for (GLuint i = 0; i < mesh->mNumFaces; i++)
	{
		aiFace face = mesh->mFaces[i];
		// Retrieve all indices of the face and store them in the indices vector
		for (GLuint j = 0; j < face.mNumIndices; j++)
			indices.push_back(face.mIndices[j]);
	}
	// Process materials
	if (mesh->mMaterialIndex >= 0)
	{
		aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];
		// We assume a convention for sampler names in the shaders. Each diffuse texture should be named
		// as 'texture_diffuseN' where N is a sequential number ranging from 1 to MAX_SAMPLER_NUMBER. 
		// Same applies to other texture as the following list summarizes:
		// Diffuse: texture_diffuseN
		// Specular: texture_specularN
		// Normal: texture_normalN

		// 1. Diffuse maps
		vector<Texture> diffuseMaps = this->loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
		textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());
		// 2. Specular maps
		vector<Texture> specularMaps = this->loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");
		textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());
	}

	// Return a mesh object created from the extracted mesh data
	return Mesh(vertices, indices, textures);
}

vector<Texture> Model::loadMaterialTextures(aiMaterial* mat, aiTextureType type, string typeName){
	vector<Texture> textures;
	for (GLuint i = 0; i < mat->GetTextureCount(type); i++)
	{
		aiString str;
		mat->GetTexture(type, i, &str);
		// Check if texture was loaded before and if so, continue to next iteration: skip loading a new texture
		GLboolean skip = false;
		for (GLuint j = 0; j < textures_loaded.size(); j++)
		{
			if (std::strcmp(textures_loaded[j].path.C_Str(), str.C_Str()) == 0)
			{
				textures.push_back(textures_loaded[j]);
				skip = true; // A texture with the same filepath has already been loaded, continue to next one. (optimization)
				break;
			}
		}
		if (!skip)
		{   // If texture hasn't been loaded already, load it
			Texture texture;
			texture.id = TextureFromFile(str.C_Str(), this->directory);
			texture.type = typeName;
			texture.path = str;
			textures.push_back(texture);
			this->textures_loaded.push_back(texture);  // Store it as texture loaded for entire model, to ensure we won't unnecesery load duplicate textures.
		}
	}
	return textures;
}


GLint TextureFromFile(const char* path, string directory)
{
	//Generate texture ID and load texture data 
	string filename = string(path);
	filename = directory + '/' + filename;
	GLuint textureID;
	glGenTextures(1, &textureID);
	int width, height;
	unsigned char* image = SOIL_load_image(filename.c_str(), &width, &height, 0, SOIL_LOAD_RGB);
	// Assign texture to ID
	glBindTexture(GL_TEXTURE_2D, textureID);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
	glGenerateMipmap(GL_TEXTURE_2D);

	// Parameters
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, 0);
	SOIL_free_image_data(image);
	return textureID;
}