OpenGL学习笔记之纹理

学习地址：纹理

文章推荐的库在ubuntu下运行出现错误，本文解析文件采用的是OpenCV库。

最终运行结果如下：

 

第一步：OpenGL必备三要素

    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", nullptr, nullptr);
    if (window == nullptr)
    {
        qDebug() << "Failed to create GLFW window";
        glfwTerminate();
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback_texture1);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        qDebug() << "Failed to initialize GLAD";
    }

 

第二步：顶点着色器和片段着色器

    // 顶点着色器
    unsigned int vertexShader, fragmentShader;
    int success;
    char infoLog[512];

    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSourceTexture1, nullptr);
    glCompileShader(vertexShader);
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog);
        qDebug() << "COMPILATION FAILED: " << infoLog;
    }

    // 片段着色器
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSourceTexture1, nullptr);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog);
        qDebug() << "COMPILATION FAILED: " << infoLog;
    }

 

第三步：创建VBO,VAO,EBO对象

我又忘记EBO具体是什么作用了。。

EBO索引缓冲数组存储索引到缓冲中，然后供OpenGL绘制的时候调用，决定要调用的点的顺序。

// 通过顶点缓冲对象VBO管理存放顶点的内存
    unsigned int VBO, VAO, EBO;
    // VAO, 顶点数组对象，批量管理以上属性
    glGenVertexArrays(1,&VAO);
    glGenBuffers(1, &EBO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

 

第四步：设置解析规则

    // 解析位置属性
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // 解析颜色属性
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    // 解析纹理属性
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

 

第五步：绑定纹理以及设置纹理属性

    unsigned int texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    // 设置横向和竖向的重复模式
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // 设置纹理过滤属性，这里设置的是线性过滤，看起来会平滑一些
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

第六步：使用OpenCV解析图片并生成纹理

    cv::Mat imgSource;
    imgSource = cv::imread("container.jpg");
    if (imgSource.empty()) {
        qDebug() << "read image error";
    }
    int width, height, nrChannels;
    width = imgSource.cols;
    height = imgSource.rows;
    nrChannels = imgSource.channels();

    // 生成纹理
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, imgSource.data);

    // 为当前绑定的纹理自动生成所有需要的多级渐远纹理
    glGenerateMipmap(GL_TEXTURE_2D);

 

第七步：绘制

glBindTexture(GL_TEXTURE_2D, texture);
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

 

总结：纹理的使用和之前绘制三角形类似，流程都是：顶点着色器、片段着色器、着色器程序、创建VAO、VBO、EBO(VBO是用来管理存放顶点的内存、VAO是批量管理VBO，EBO是决定绘制的点的顺序)、设置解析规则、创建纹理，最后通过glDrawElements（或者DrawArrays)绘制。

完整代码如下：

#include "texturetest1.h"
#include 
#include 
#include 
#include 

const char* vertexShaderSourceTexture1 = "#version 330 core\n"
        "layout (location = 0) in vec3 aPos;\n"
        "layout (location = 1) in vec3 aColor;\n"
        "layout (location = 2) in vec2 aTexCoord;\n"
        "out vec3 ourColor;\n"
        "out vec2 TexCoord;\n"
        "void main()\n"
        "{\n"
            "gl_Position = vec4(aPos, 1.0);\n"
            "ourColor = aColor;\n"
            "TexCoord = vec2(aTexCoord.x, aTexCoord.y);\n"
        "}";

const char* fragmentSourceTexture1 = "#version 330 core\n"
        "out vec4 FragColor;\n"
        "in vec3 ourColor;\n"
        "in vec2 TexCoord;\n"
        "uniform sampler2D texture1;\n"
        "void main()\n"
        "{\n"
            "FragColor = texture(texture1, TexCoord) * vec4(ourColor, 1.0) ;\n"
        "}";

void framebuffer_size_callback_texture1(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}

void processInputTexture1(GLFWwindow * window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, true);
    }
}
TextureTest1::TextureTest1()
{

    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", nullptr, nullptr);
    if (window == nullptr)
    {
        qDebug() << "Failed to create GLFW window";
        glfwTerminate();
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback_texture1);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        qDebug() << "Failed to initialize GLAD";
    }


    // 顶点着色器
    unsigned int vertexShader, fragmentShader;
    int success;
    char infoLog[512];

    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSourceTexture1, nullptr);
    glCompileShader(vertexShader);
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog);
        qDebug() << "COMPILATION FAILED: " << infoLog;
    }

    // 片段着色器
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSourceTexture1, nullptr);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog);
        qDebug() << "COMPILATION FAILED: " << infoLog;
    }

    float vertices[] = {
    //     ---- 位置 ----       ---- 颜色 ----     - 纹理坐标 -
         0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f,   // 右上
         0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f,   // 右下
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f,   // 左下
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f    // 左上
    };

    unsigned int indices[] = {
        0, 1, 3, // first triangle
        1, 2, 3  // second triangle
    };

    // 创建着色器程序
    unsigned int shaderProgram = glCreateProgram();
    // 现在我们需要把之前编译的着色器附加到程序对象上，然后用glLinkProgram链接它们
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    // 在glUseProgram函数调用之后, 删除着色器对象，我们不再需要它们了
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);


    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    // 通过顶点缓冲对象VBO管理存放顶点的内存
    unsigned int VBO, VAO, EBO;
    // VAO, 顶点数组对象，批量管理以上属性
    glGenVertexArrays(1,&VAO);
    glGenBuffers(1, &EBO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // color attribute
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    // texture coord attribute
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    unsigned int texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    // 设置横向和竖向的重复模式
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // 设置纹理过滤属性，这里设置的是线性过滤，看起来会平滑一些
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    cv::Mat imgSource;
    imgSource = cv::imread("container.jpg");
    if (imgSource.empty()) {
        qDebug() << "read image error";
    }
    int width, height, nrChannels;
    width = imgSource.cols;
    height = imgSource.rows;
    nrChannels = imgSource.channels();

    // 生成纹理
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, imgSource.data);

    // 为当前绑定的纹理自动生成所有需要的多级渐远纹理
    glGenerateMipmap(GL_TEXTURE_2D);

    while (!glfwWindowShouldClose(window)) {
        processInputTexture1(window);
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glBindTexture(GL_TEXTURE_2D, texture);
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);
        glfwSwapBuffers(window);
        glfwPollEvents();
    }


    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    glfwTerminate();
}