obj + mlt 3d model 呈現錯誤的顏色

Question

我正在使用 OpenGL v.3.3。 以及來自 learnopengl.com 的完整源代碼示例。 我可以從教程（nanosuit.obj）中運行帶紋理的 model，但是當我嘗試加載另一個沒有紋理但帶有.mtl 文件的.obj 模型時，它顯示為深色。 我認為問題可能出在我用來加載模型的着色器中，但我不知道如何重做着色器的代碼來解決我的問題。

這是我用來渲染 model 的主要功能：

 void COpenGLControl::oglInitialize(void)
    {

        static PIXELFORMATDESCRIPTOR pfd =
        {
            sizeof(PIXELFORMATDESCRIPTOR),
            1,
            PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
            PFD_TYPE_RGBA,
            32, // bit depth
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            16, // z-buffer depth
            0, 0, 0, 0, 0, 0, 0,
        };

        // Get device context only once.
        hdc = GetDC()->m_hDC;

        // Pixel format.
        m_nPixelFormat = ChoosePixelFormat(hdc, &pfd);
        SetPixelFormat(hdc, m_nPixelFormat, &pfd);

        // Create the OpenGL Rendering Context.
        hrc = wglCreateContext(hdc);
        wglMakeCurrent(hdc, hrc);

        if (!gladLoadGL())
        {
            AfxMessageBox(L"Error loading glad");
            return;
        }
        // configure global opengl state
        // -----------------------------
        glEnable(GL_DEPTH_TEST);

        // build and compile shaders
        ourShader = Shader("resource/shaders/modelLoading.vs", "resource/shaders/modelLoading.frag");

        // load models
        ourModel = Model("resource/models/car12/LaFerrari.obj");



        // Send draw request
        OnDraw(NULL);
    }

    void COpenGLControl::oglDrawScene(void)
    {

        // render
        // ------
        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // don't forget to enable shader before setting uniforms
        ourShader.use();

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)900 / (float)900, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        ourShader.setMat4("projection", projection);
        ourShader.setMat4("view", view);

        // render the loaded model
        glm::mat4 model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));
        model = glm::scale(model, glm::vec3(0.010f, 0.010f, 0.010f));
        model = glm::rotate(model, glm::radians(-30.0f), glm::vec3(0.0f, 1.0f, 0.0f));
        model = glm::rotate(model, glm::radians(20.0f), glm::vec3(1.0f, 0.0f, 0.0f));
        ourShader.setMat4("model", model);
        ourModel.Draw(ourShader);
    }

model.cpp

 #include "pch.h"
    #include "model.h"

    Model::Model(void)
    {

    }

    Model::Model(string const& path, bool gamma) 
    {
        loadModel(path);
    }


    void Model::Draw(Shader shader)
    {
        for (unsigned int i = 0; i < meshes.size(); i++)
            meshes[i].Draw(shader);
    }

    void Model::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);
    }

    void Model::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 Model::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
            if (!mesh->mVertices == NULL)
            {
                vector.x = mesh->mVertices[i].x;
                vector.y = mesh->mVertices[i].y;
                vector.z = mesh->mVertices[i].z;
                vertex.Position = vector;
            }
            else
            {
                vertex.Position = glm::vec3(0.0f, 0.0f, 0.0f);
                //AfxMessageBox(L"Positions is NULL");
            }

            // normals
            if (!mesh->mNormals == NULL)
            {
                vector.x = mesh->mNormals[i].x;
                vector.y = mesh->mNormals[i].y;
                vector.z = mesh->mNormals[i].z;
                vertex.Normal = vector;
            }
            else
            {
                vertex.Normal = glm::vec3(0.0f, 0.0f, 0.0f);
                //AfxMessageBox(L"Normals is NULL");
            }

            // 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);
                //AfxMessageBox(L"TextCoords is NULL");
            }

            // tangent
            if (!mesh->mTangents == NULL)
            {
                vector.x = mesh->mTangents[i].x;
                vector.y = mesh->mTangents[i].y;
                vector.z = mesh->mTangents[i].z;
                vertex.Tangent = vector;
            }
            else
            {
                vertex.Tangent = glm::vec3(0.0f, 0.0f, 0.0f);
                //AfxMessageBox(L"TextCoords is NULL");
            }

            // bitangent
            if (!mesh->mBitangents == NULL)
            {
                vector.x = mesh->mBitangents[i].x;
                vector.y = mesh->mBitangents[i].y;
                vector.z = mesh->mBitangents[i].z;
                vertex.Bitangent = vector;
            }
            else
            {
                vertex.Bitangent = glm::vec3(0.0f, 0.0f, 0.0f);
                //AfxMessageBox(L"Bitangent is NULL");
            }

            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];


        aiColor3D color;
        Material mat;
        // 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);
    }

    vector<Texture> Model::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, false);
                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 Model::TextureFromFile(const char* path, const string& directory, bool gamma)
    {
        //string filename = string(path);
        //filename = directory + '/' + filename;

        string filename = string(path);
        if (directory.find(R"(/)") != std::string::npos)
        {
            filename = directory + R"(/)" + filename;
        }
        else if (directory.find(R"(\\)") != std::string::npos)
        {
            filename = directory + R"(\\)" + filename;
        }

        stbi_set_flip_vertically_on_load(false);
        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;

    }

着色器： frag

#version 330 core
in vec2 TexCoords;
out vec4 color;

uniform sampler2D texture_diffuse;
void main( )
{
    color = vec4( texture( texture_diffuse, TexCoords ));
}

對比

#version 330 core
layout ( location = 0 ) in vec3 position;
layout ( location = 1 ) in vec3 normal;
layout ( location = 2 ) in vec2 texCoords;

out vec2 TexCoords;

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

void main( )
{
    gl_Position = projection * view * model * vec4( position, 1.0f );
    TexCoords = texCoords;
}

還附上圖片（深色圖片是我程序的結果，彩色圖片是AbViewer free obj viewer 結果）。 請幫我找到解決方案，我做錯了什么？

Answer 1

您需要在繪制調用之前綁定當前紋理。 您沒有代碼可以為頂點緩沖區的頂點設置任何顏色信息。

因此，如果沒有任何燈光、顏色和粘合紋理，您的 model 將是黑色的:-)。