OpenGL：不能不渲染三角形

Question

编写代码并运行后，没有任何效果。我设法填充了背景，但没有别的。

这是我的代码：

#include <iostream>
#include <glad\glad.h>
#include <GLFW\glfw3.h>

const int WINDOW_WIDTH = 800;
const int WINDOW_HEIGHT = 600;

const char *vertexShaderSource = "#version 450 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";

const char *fragmentShaderSource = "#version 450 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
    "FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\0";

void framebuffer_size_callback(GLFWwindow* window, int width, int height);

int main()
{
    // Initializes GLFW and passes window hints 
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 5);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // Creates GLFWwindow called window
    GLFWwindow* window = glfwCreateWindow(WINDOW_WIDTH, WINDOW_HEIGHT, "LearningOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // Check if GLAD is initialized
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f,  0.5f, 0.0f
    };

    int success;
    char infoLog[512];


    // Creating Vertex Shader Object
    unsigned int vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    // Creating Fragment Shader Object
    unsigned int fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    // Shader program
    unsigned int shaderProgram;
    shaderProgram = glCreateProgram();

    // Attatching both shaders to the program and then linking them
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // Interpreting vertex data 
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // Generating a Vertex Array Object
    unsigned int VAO;
    unsigned int VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // Size of rendering window 
    glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); 

    // While window is open
    while (!glfwWindowShouldClose(window))
    {
        // Finally
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glBindVertexArray(VAO);
        glUseProgram(shaderProgram);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    // If loop is exited, terminate all allocated resources and close the program
    glfwTerminate();
    return 0;
}

// Frame buffer function that resizes the viewport when the window gets resized
void framebuffer_size_callback(GLFWwindow * window, int width, int height)
{
    glViewport(0, 0, width, height);
}

Answer 1

在绑定 VAO 之前，不要尝试启用或设置顶点属性指针。在 Core 上下文中不会做任何有用的事情。

绑定一个VAO然后启用/设置属性：

unsigned int VBO;
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

// Generating a Vertex Array Object
unsigned int VAO;
glGenVertexArrays(1, &VAO);
glBindVertexArray( VAO );

// Interpreting vertex data 
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);

Answer 2

我注意到您的代码存在一些错误或问题：第一个明显的错误是在您调用以下代码后：

glfwMakeContextCurrent(window);

你应该打电话给：

glfwSetFramebufferSizeCallback( window, framebuffer_size_callback );

这应该在使窗口成为当前上下文之后并且在所有 OpenGL 内容之前完成。

---

我看到的第二个问题是在您的 VAO 和 VBO 的设置中，在从您的着色器中读取信息后，您的某些东西的顺序不正确，您甚至错过了一两个电话从您的代码的这一部分：

// Interpreting vertex data 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

// Generating a Vertex Array Object
unsigned int VAO;
unsigned int VBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

// Size of rendering window 
glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); 

• 首先，您应该在调用glVertexAttribPointer() 和glEnableVertexAtrribArray() 之前创建和初始化VBO 和VAO。从 API - 库的角度来考虑这一点。如何启用指向内存中尚不存在的东西的指针？

• 其次，您错过了对glBindVertexArray(VAO); 的调用，这应该是在您生成VAO 和VBO 之后。

• 第三，最后两行代码我已经解释了函数glfwSetFramebufferSizeCallback()和它应该放在哪里；但对于这一部分，我将解释原因。这是设置视口的函数，因为它是回调类型的函数。将窗口设置为当前上下文后；这是你想告诉 OpenGL 你的视口或窗口的大小，以便它知道Screen Size 在将所有顶点数据转换为屏幕空间坐标时使用。通过修复此问题，您将不必单独调用glViewport()；因为这就是回调函数为您所做的。

这部分代码应该如下所示：

unsigned int VBO, VAO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
glBindVertexArray(VAO);

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

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
glBindBuffer(GL_ARRAY_BUFFER, 0); 

// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
glBindVertexArray(0); 

---

我看到的最后一件事是在你的 while 循环中进行渲染，并且在你的循环之后：

// While window is open
while (!glfwWindowShouldClose(window))
{
   // Finally
   glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
   glClear(GL_COLOR_BUFFER_BIT);
   glBindVertexArray(VAO);
   glUseProgram(shaderProgram);
   glDrawArrays(GL_TRIANGLES, 0, 3);

   glfwSwapBuffers(window);
   glfwPollEvents();
}
// If loop is exited, terminate all allocated resources and close the program
glfwTerminate();
return 0;

我在这里看到两个问题：

首先，使用程序和绑定顶点数组的顺序是倒序的，应该是：

glUseProgram(shaderProgram);
glBindVertexArray(VAO);

在你的while循环之后和glfwTerimate()调用之前，你应该删除你的顶点数组和缓冲区

glDeleteVertexArrays( 1, &VAO );
glDeleteBuffers( 1, &VBO );

---

如果这些简单的更正不能解决您的问题，您可以尝试另一件事。您可以尝试将OpenGL 的版本从4.5 更改为3.3，因为他们的GLSL Shader 语言的版本略有不同。

如果这不起作用，那么它可能与您设置正在使用的外部库的方式有关。

---

总结

在尝试设置任何顶点数据之前，您首先必须设置视口。接下来，您必须先设置您的VAO 和VBO 信息，然后才能调用glVertexAtrribPointer() 和glEnableVertexAttribArray()，并且不要忘记在调用后调用glBindVertexArray(VAO) 以生成它们。在所有初始化都按正确顺序之后，在渲染循环中使用它时，您应该在glBindVertexArray 之前调用glUseProgram。最后，在您的渲染循环之后，您应该进行适当的调用以删除您的顶点数组和缓冲区。如果这些都失败了，那么您可以尝试更改OpenGl - GLSL 的版本并检查所有正在使用的外部库的设置。