Use assimp library to read MTL file data

Recently in use opengl Do school homework , When reading the model, I encountered the problem that the material cannot be displayed , Through research obj And mtl The reason is found in the file format .

Because I used to use the reading class made by others , Models with maps can be processed normally , But this time the model has no mapping , Materials are directly assigned by attributes , Such as

among ,Ka Represents ambient light ,Kd Represents diffuse light ,Ks Represents specular highlights .

In order to read these data , It has been modified in the existing code （ The code is at the bottom ）.assimp In fact, it provides a method to read these data , We just keep it in mesh In information , And pass in shaders to use .

		aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];
		Material mat;
		aiColor3D color;
		// Read mtl File vertex data 
		material->Get(AI_MATKEY_COLOR_AMBIENT, color);
		mat.Ka = glm::vec4(color.r, color.g, color.b,1.0);

among AI_MATKEY_COLOR_AMBIENT That is, the information corresponding to the ambient light .

When data is passed into the shader , Used ubo object , because vbo The vertex, normal and other information of the model have been saved in , So deal with materials separately .

 

The code is as follows ：

mesh.h

#pragma once
#ifndef MESH_H
#define MESH_H

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

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

#include "shader_m.h"

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <vector>
using namespace std;

struct Vertex {
	// position
	glm::vec3 Position;
	// normal
	glm::vec3 Normal;
	// texCoords
	glm::vec2 TexCoords;
	// tangent
	glm::vec3 Tangent;
	// bitangent
	glm::vec3 Bitangent;
};

struct Material {
	// Material color illumination 
	glm::vec4 Ka;
	// Diffuse reflection 
	glm::vec4 Kd;
	// Specular reflex 
	glm::vec4 Ks;
};

struct Texture {
	unsigned int id;
	string type;
	string path;
};

class Mesh {
public:
	/*  Mesh Data  */
	vector<Vertex> vertices;
	vector<unsigned int> indices;
	vector<Texture> textures;
	Material mats;
	unsigned int VAO;
	unsigned int uniformBlockIndex;
	/*  Functions  */
	// constructor
	Mesh(vector<Vertex> vertices, vector<unsigned int> indices, vector<Texture> textures, Material mat)
	{
		this->vertices = vertices;
		this->indices = indices;
		this->textures = textures;
		this->mats = mat;
		// now that we have all the required data, set the vertex buffers and its attribute pointers.
		setupMesh();
	}

	// render the mesh
	void Draw(Shader shader)
	{
		// bind appropriate textures
		unsigned int diffuseNr = 1;
		unsigned int specularNr = 1;
		unsigned int normalNr = 1;
		unsigned int heightNr = 1;
		for (unsigned int i = 0; i < textures.size(); i++)
		{
			glActiveTexture(GL_TEXTURE0 + i); // active proper texture unit before binding
											  // retrieve texture number (the N in diffuse_textureN)
			string number;
			string name = textures[i].type;
			if (name == "texture_diffuse")
				number = std::to_string(diffuseNr++);
			else if (name == "texture_specular")
				number = std::to_string(specularNr++); // transfer unsigned int to stream
			else if (name == "texture_normal")
				number = std::to_string(normalNr++); // transfer unsigned int to stream
			else if (name == "texture_height")
				number = std::to_string(heightNr++); // transfer unsigned int to stream

													 // now set the sampler to the correct texture unit

			glUniform1i(glGetUniformLocation(shader.ID, (name + number).c_str()), i);
			// and finally bind the texture
			glBindTexture(GL_TEXTURE_2D, textures[i].id);
		}

		// draw mesh
		glBindVertexArray(VAO);
		glBindBufferRange(GL_UNIFORM_BUFFER,0, uniformBlockIndex,0,sizeof(Material));
		glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0);
		glBindVertexArray(0);

		// always good practice to set everything back to defaults once configured.
		glActiveTexture(GL_TEXTURE0);
	}

private:
	/*  Render data  */
	unsigned int VBO, EBO;

	/*  Functions    */
	// initializes all the buffer objects/arrays
	void setupMesh()
	{
		// create buffers/arrays
		glGenVertexArrays(1, &VAO);
		glGenBuffers(1, &VBO);
		glGenBuffers(1, &EBO);
		glGenBuffers(1, &uniformBlockIndex);

		glBindVertexArray(VAO);
		// load data into vertex buffers
		glBindBuffer(GL_ARRAY_BUFFER, VBO);
		// A great thing about structs is that their memory layout is sequential for all its items.
		// The effect is that we can simply pass a pointer to the struct and it translates perfectly to a glm::vec3/2 array which
		// again translates to 3/2 floats which translates to a byte array.
		glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(Vertex)+ sizeof(mats), &vertices[0], GL_STATIC_DRAW);
		glBindBuffer(GL_UNIFORM_BUFFER, uniformBlockIndex);
		glBufferData(GL_UNIFORM_BUFFER,sizeof(mats),(void*)(&mats), GL_STATIC_DRAW);

		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned int), &indices[0], GL_STATIC_DRAW);

		// set the vertex attribute pointers
		// vertex Positions
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)0);
		// vertex normals
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Normal));
		// vertex texture coords
		glEnableVertexAttribArray(2);
		glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, TexCoords));
		// vertex tangent
		glEnableVertexAttribArray(3);
		glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Tangent));
		// vertex bitangent
		glEnableVertexAttribArray(4);
		glVertexAttribPointer(4, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Bitangent));
		
	}
};
#endif

model.h

#pragma once
#ifndef MODEL_H
#define MODEL_H

#include <glad/glad.h> 

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

#define STB_IMAGE_IMPLEMENTATION 
#include "stb_image.h"

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

#include "mesh.h"
#include "shader_m.h"

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <map>
#include <vector>
using namespace std;

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

class Model
{
public:
	/*  Model Data */
	vector<Texture> textures_loaded;	// stores all the textures loaded so far, optimization to make sure textures aren't loaded more than once.
	vector<Mesh> meshes;
	string directory;
	bool gammaCorrection;

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

	// draws the model, and thus all its meshes
	void Draw(Shader shader)
	{
		for (unsigned int i = 0; i < meshes.size(); i++)
			meshes[i].Draw(shader);
	}

private:
	/*  Functions   */
	// loads a model with supported ASSIMP extensions from file and stores the resulting meshes in the meshes vector.
	void loadModel(string const &path)
	{
		// read file via ASSIMP
		Assimp::Importer importer;
		const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);
		
		// check for errors
		if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) // if is Not Zero
		{
			cout << "ERROR::ASSIMP:: " << importer.GetErrorString() << endl;
			return;
		}
		// retrieve the directory path of the filepath
		directory = path.substr(0, path.find_last_of('/'));

		// process ASSIMP's root node recursively
		processNode(scene->mRootNode, scene);
		
	}

	// processes a node in a recursive fashion. Processes each individual mesh located at the node and repeats this process on its children nodes (if any).
	void processNode(aiNode *node, const aiScene *scene)
	{
		// process each mesh located at the current node
		for (unsigned int i = 0; i < node->mNumMeshes; i++)
		{
			// the node object only contains indices to index the actual objects in the scene. 
			// the scene contains all the data, node is just to keep stuff organized (like relations between nodes).
			aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
			meshes.push_back(processMesh(mesh, scene));
		}
		// after we've processed all of the meshes (if any) we then recursively process each of the children nodes
		for (unsigned int i = 0; i < node->mNumChildren; i++)
		{
			processNode(node->mChildren[i], scene);
		}

	}

	Mesh processMesh(aiMesh *mesh, const aiScene *scene)
	{
		// data to fill
		vector<Vertex> vertices;
		vector<unsigned int> indices;
		vector<Texture> textures;
		// Walk through each of the mesh's vertices
		for (unsigned int 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);
			// tangent
			vector.x = mesh->mTangents[i].x;
			vector.y = mesh->mTangents[i].y;
			vector.z = mesh->mTangents[i].z;
			vertex.Tangent = vector;
			// bitangent
			vector.x = mesh->mBitangents[i].x;
			vector.y = mesh->mBitangents[i].y;
			vector.z = mesh->mBitangents[i].z;
			vertex.Bitangent = vector;
			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 (unsigned int 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 (unsigned int j = 0; j < face.mNumIndices; j++)
				indices.push_back(face.mIndices[j]);
		}
		// process materials
		aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];
		Material mat;
		aiColor3D color;

		// Read mtl File vertex data 

		material->Get(AI_MATKEY_COLOR_AMBIENT, color);
		mat.Ka = glm::vec4(color.r, color.g, color.b,1.0);
		material->Get(AI_MATKEY_COLOR_DIFFUSE, color);
		mat.Kd = glm::vec4(color.r, color.g, color.b,1.0);
		material->Get(AI_MATKEY_COLOR_SPECULAR, color);
		mat.Ks = glm::vec4(color.r, color.g, color.b,1.0);



		// 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 = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
		textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());
		// 2. specular maps
		vector<Texture> specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");
		textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());
		// 3. normal maps
		std::vector<Texture> normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");
		textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());
		// 4. height maps
		std::vector<Texture> heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");
		textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());

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

	// checks all material textures of a given type and loads the textures if they're not loaded yet.
	// the required info is returned as a Texture struct.
	vector<Texture> loadMaterialTextures(aiMaterial *mat, aiTextureType type, string typeName)
	{
		vector<Texture> textures;
		for (unsigned int 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
			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; // 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.C_Str();
				textures.push_back(texture);
				textures_loaded.push_back(texture);  // store it as texture loaded for entire model, to ensure we won't unnecesery load duplicate textures.
			}
		}
		return textures;
	}
};


unsigned int TextureFromFile(const char *path, const string &directory, bool gamma)
{
	string filename = 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

Vertex shader ：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;

uniform Mat{
	vec4 aAmbient;
	vec4 aDiffuse;
	vec4 aSpecular;
};
out vec3 FragPos;
out vec3 Normal;

out vec4 Ambient;
out vec4 Diffuse;
out vec4 Specular;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{

    FragPos = vec3( model * vec4(aPos, 1.0));
    //Normal =vec3(projection * vec4(mat3(transpose(inverse(view * model))) * aNormal,0.0));  
	Normal = mat3(transpose(inverse(model))) * aNormal;  
	Ambient = aAmbient;
	Diffuse = aDiffuse;
	Specular = aSpecular;

	
    gl_Position = projection * view * vec4(FragPos, 1.0);
}

Fragment Shader ：

#version 330 core
out vec4 FragColor;

struct Light {
    vec3 position;  
  
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
	
    float constant;
    float linear;
    float quadratic;
};

in vec3 FragPos;  
in vec3 Normal;  
in vec2 TexCoords;
// from Mtl Data read in 
//Material
in vec4 Ambient;
in vec4 Diffuse;
in vec4 Specular;

uniform vec3 viewPos;
uniform Light light;

uniform float shininess;

void main()
{    
	// ambient
    vec3 ambient = light.ambient * Diffuse.rgb;
  	
    // diffuse 
    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(light.position - FragPos);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse =light.diffuse * diff *Diffuse.rgb;  
      
    // attenuation
    float distance    = length(light.position - FragPos);
    float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));    
	// specular
    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);  
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), shininess);
    vec3 specular = light.specular * spec *   Specular.rgb;  
	
    //ambient  *= attenuation;  
    diffuse   *= attenuation; 
    specular *= attenuation; 
	  
    vec3 result = ambient + diffuse +specular;
    FragColor = vec4(result ,1.0);
}