model.h

#ifndef MODEL_H
#define MODEL_H

#include <glad/glad.h> // holds all OpenGL type declarations

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>

#include "stb_image.h"
#include "shader.h"
#include "mesh.h"

#include <string>
#include <vector>

unsigned int TextureFromFile(const char *path, const std::string &directory, bool gamma = false);

class Model{
    public:
        //model data
        std::vector<Texture> textures_loaded; //stores all textures loaded so we don't reload already loaded
        std::vector<Mesh> meshes;
        std::string directory;
        bool gammaCorrection;

        //constructor expects filepath to 3D model
        Model(std::string const &path, bool gamma = false) : gammaCorrection(gamma){
            loadModel(path);
        }

        //draws all the meshes
        void Draw(Shader &shader){
            for(unsigned int i = 0; i < meshes.size(); i++){
                meshes[i].Draw(shader);
            }
        }
    private:
        void loadModel(std::string path){
            Assimp::Importer importer;
            const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);

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

            processNode(scene->mRootNode, scene);
        }

        //recursivelly call itself untill all mesh indices have been fufilled
        void processNode(aiNode* node, const aiScene* scene){
            //process all the meshes of node
            for(unsigned int i = 0; i  < node->mNumMeshes; i++){
                aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
                meshes.push_back(processMesh(mesh, scene));
            }

            //if node has child nodes we want to process them aswell
            for(unsigned int i = 0; i < node->mNumChildren; i++){
                processNode(node->mChildren[i], scene);
            }
        };

        Mesh processMesh(aiMesh* mesh, const aiScene* scene){
            std::vector<Vertex> vertices;
            std::vector<unsigned int> indices;
            std::vector<Texture> textures;

            for(unsigned int i = 0; i < mesh->mNumVertices; i++){
                Vertex vertex;
                //process positions, normals, and texCoords
                glm::vec3 vector;
                vector.x = mesh->mVertices[i].x;
                vector.y = mesh->mVertices[i].y;
                vector.z = mesh->mVertices[i].z;
                vertex.Position = vector;

                //normals
                if (mesh->HasNormals())
                {
                    vector.x = mesh->mNormals[i].x;
                    vector.y = mesh->mNormals[i].y;
                    vector.z = mesh->mNormals[i].z;
                    vertex.Normal = vector;
                }

                //textures (2d array since assimp allows for a max of 8 different set of TexCoords)
                if(mesh->mTextureCoords[0]){
                    glm::vec2 vec;
                    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);
            }

            //process indices
            for(unsigned int i = 0; i < mesh->mNumFaces; i++){
                aiFace face = mesh->mFaces[i];//triangle
                for(unsigned int j = 0; j < face.mNumIndices; j++){
                    indices.push_back(face.mIndices[j]);
                }
            }

            //process textures
            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
            std::vector<Texture> diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
            textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());
            // 2. specular maps
            std::vector<Texture> specularMaps = 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);
        }
        
        //helper to retrieve texture file location, loads, generates, and stores them in a Vertex Struct
        std::vector<Texture> loadMaterialTextures(aiMaterial* mat, aiTextureType type, std::string typeName){
            std::vector<Texture> textures;
            for(unsigned int i = 0; i < mat->GetTextureCount(type); i++){
                aiString str;
                mat->GetTexture(type, i, &str);
                bool skip = false;
                for(unsigned int j = 0; j < textures_loaded.size(); j++){
                    if(std::strcmp(textures_loaded[j].path.data(), str.C_Str()) == 0)
                    {
                        textures.push_back(textures_loaded[j]);
                        skip = true;
                        break;
                    }
                }
                if(!skip){
                    //if a texture has not been loaded we can load it
                    Texture texture;
                    texture.id = TextureFromFile(str.C_Str(), this->directory);
                    texture.type = typeName;
                    texture.path = str.C_Str();
                    textures.push_back(texture);
                    textures_loaded.push_back(texture); //store as texture for entire model
                }
            }
            return textures;
        }

};

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int TextureFromFile(const char *path, const std::string &directory, bool gamma)
{
    std::string filename = std::string(path);
    filename = directory + '/' + filename;

    unsigned int textureID;
    glGenTextures(1, &textureID);
    
    int width, height, nrComponents;
    unsigned char *data = stbi_load(filename.c_str(), &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        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);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}



#endif