opengl - assimp 未正确加载

Question

我在使用 Assimp 加载网格体时遇到问题。即使在环境照明后，某些面孔也不会显示。我正在使用 learnopengl.com 教程中提供的代码来加载网格。我在下面提供了我的网格和模型源以及屏幕截图。如果有人可以帮助解决问题，我将非常感激。

网格.h

#pragma once
// Std. Includes
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <vector>
using namespace std;
// GL Includes
#include <GL/glew.h> // Contains all the necessery OpenGL includes
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>


struct Vertex {
    // Position
    glm::vec3 Position;
    // Normal
    glm::vec3 Normal;
    // TexCoords
    glm::vec2 TexCoords;
};

struct Texture {
    GLuint id;
    string type;
    aiString path;
};

class Mesh {
public:
    /*  Mesh Data  */
    vector<Vertex> vertices;
    vector<GLuint> indices;
    vector<Texture> textures;

    /*  Functions  */
    // Constructor
    Mesh(vector<Vertex> vertices, vector<GLuint> indices, vector<Texture> textures)
    {
        this->vertices = vertices;
        this->indices = indices;
        this->textures = textures;

        // Now that we have all the required data, set the vertex buffers and its attribute pointers.
        this->setupMesh();
    }

    // Render the mesh
    void Draw(Shader shader)
    {
        // Bind appropriate textures
        GLuint diffuseNr = 1;
        GLuint specularNr = 1;
        GLuint reflectionNr = 1;

        for (GLuint i = 0; i < this->textures.size(); i++)
        {
            glActiveTexture(GL_TEXTURE0 + i); // Active proper texture unit before binding
            // Retrieve texture number (the N in diffuse_textureN)
            stringstream ss;
            string number;
            string name = this->textures[i].type;
            if (name == "texture_diffuse")
                ss << diffuseNr++; // Transfer GLuint to stream
            else if (name == "texture_specular")
                ss << specularNr++; // Transfer GLuint to stream
            else if (name == "texture_reflection")  // We'll now also need to add the code to set and bind to reflection textures
                ss << reflectionNr++;
            number = ss.str();
            // Now set the sampler to the correct texture unit
            glUniform1i(glGetUniformLocation(shader.program, (name + number).c_str()), i);

            // And finally bind the texture
            glBindTexture(GL_TEXTURE_2D, this->textures[i].id);
        }
        glActiveTexture(GL_TEXTURE0); // Always good practice to set everything back to defaults once configured.

        // Also set each mesh's shininess property to a default value (if you want you could extend this to another mesh property and possibly change this value)
        //glUniform1f(glGetUniformLocation(shader.Program, "material.shininess"), 16.0f);

        // Draw mesh
        glBindVertexArray(this->VAO);
        glDrawElements(GL_TRIANGLES, this->indices.size(), GL_UNSIGNED_INT, 0);
        glBindVertexArray(0);
    }

private:
    /*  Render data  */
    GLuint VAO, VBO, EBO;

    /*  Functions    */
    // Initializes all the buffer objects/arrays
    void setupMesh()
    {
        // Create buffers/arrays
        glGenVertexArrays(1, &this->VAO);
        glGenBuffers(1, &this->VBO);
        glGenBuffers(1, &this->EBO);

        glBindVertexArray(this->VAO);
        // Load data into vertex buffers
        glBindBuffer(GL_ARRAY_BUFFER, this->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, this->vertices.size() * sizeof(Vertex), &this->vertices[0], GL_STATIC_DRAW);

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->EBO);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, this->indices.size() * sizeof(GLuint), &this->indices[0], GL_STATIC_DRAW);

        // Set the vertex attribute pointers
        // Vertex Positions
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)0);
        // Vertex Normals
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, Normal));
        // Vertex Texture Coords
        glEnableVertexAttribArray(2);
        glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, TexCoords));

        glBindVertexArray(0);
    }
};

模型.h

#pragma once
// Std. Includes
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <map>
#include <vector>
using namespace std;
// GL Includes
#include <GL/glew.h> // Contains all the necessery OpenGL includes
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <SOIL.h>
#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>

#include "Mesh.h"

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

class Model
{
public:
    /*  Functions   */
    // Constructor, expects a filepath to a 3D model.
    Model(GLchar* path)
    {
        this->loadModel(path);
    }

    // Draws the model, and thus all its meshes
    void Draw(Shader shader)
    {
        for (GLuint i = 0; i < this->meshes.size(); i++)
            this->meshes[i].Draw(shader);
    }

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

    /*  Functions   */
    // Loads a model with supported ASSIMP extensions from file and stores the resulting meshes in the meshes vector.
    void loadModel(string path)
    {
        // Read file via ASSIMP
        Assimp::Importer importer;
        const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs);
        // 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
        this->directory = path.substr(0, path.find_last_of('/'));

        // Process ASSIMP's root node recursively
        this->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 (GLuint 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.
            aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
            this->meshes.push_back(this->processMesh(mesh, scene));
        }
        // After we've processed all of the meshes (if any) we then recursively process each of the children nodes
        for (GLuint i = 0; i < node->mNumChildren; i++)
        {
            // Child nodes are actually stored in the node, not in the scene (which makes sense since nodes only contain
            // links and indices, nothing more, so why store that in the scene)
            this->processNode(node->mChildren[i], scene);
        }

    }

    Mesh 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());
            // 3. Reflection maps (Note that ASSIMP doesn't load reflection maps properly from wavefront objects, so we'll cheat a little by defining the reflection maps as ambient maps in the .obj file, which ASSIMP is able to load)
            vector<Texture> reflectionMaps = this->loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_reflection");
            textures.insert(textures.end(), reflectionMaps.begin(), reflectionMaps.end());
        }

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

    // 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 (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 (textures_loaded[j].path == str)
                {
                    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;
}

截图

1st screenshot

2nd screenshot

Answer 1

正如我在这里看到的

glDrawElements(GL_TRIANGLES, this->indices.size(), GL_UNSIGNED_INT, 0);

将所有顶点绘制为三角形。这就是从 assimp 加载索引的方式

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

这里有一个问题 - 脸部没有恰好 3 个顶点(即使您在加载时使用 aiProcess_Triangulate)，这会破坏 GL_TRIANGLES 的绘制。使用 aiProcess_Triangulate 将会出现具有 <= 3 个顶点的面(例如三角形和直线)。您可以忽略不是三角形的面，这应该可以修复绘图。这是一个固定的不定填充周期:

    for (GLuint i = 0; i < mesh->mNumFaces; i++)
    {
        aiFace face = mesh->mFaces[i];
        if (face.mNumIndices < 3) {
            continue;
        }
        assert(face.mNumIndices == 3);
        for (GLuint j = 0; j < face.mNumIndices; j++)
            indices.push_back(face.mIndices[j]);
    }