我无法让我的 OpenGL 程序渲染三角形

Question

所以我在 OpenGL 中编写了一个模型加载器，它确实加载了模型，但由于某种原因，我在屏幕上看不到生成的三角形。自己看看吧：

#define GLEW_STATIC

#include <GL\glew.h>    // Graphics Libraries
#include <GLFW\glfw3.h>

#include <iostream>
#include <fstream>
#include <vector>
#include <string>

int main()
{
    std::cout << "Please enter the name of the mesh file: ";
    std::string FileName;
    std::cin >> FileName;

    std::cout << "You entered: " << FileName << std::endl;

    if (!glfwInit())
    {
        std::cout << "Failed to initialize GLFW" << std::endl;
        system("Pause");
        return EXIT_FAILURE;
    }

    std::cout << "GLFW 3.0.4 Initialized" << std::endl;

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);

    GLFWwindow* Window = glfwCreateWindow(800, 600, "Window", NULL, NULL);
    glfwMakeContextCurrent(Window);

    if (Window == NULL)
    {
        std::cout << "Failed to create an OpenGL 3.3 context" << std::endl;
        system("Pause");
        return EXIT_FAILURE;
    }

    std::cout << "Created an OpenGL 3.3 context" << std::endl;

    glewExperimental = GL_TRUE; 

    if (glewInit() != GLEW_OK)
    {
        std::cout << "Failed to initialize GLEW 1.11.0" << std::endl;
        system("Pause");
        return EXIT_FAILURE;
    }

    std::ifstream FileStream(FileName);
    std::vector <float> Vertices;

    if (!FileStream)
    {
        std::cout << "An error was encountered while opening "<< FileName << std::endl;
        system("Pause");
        return EXIT_FAILURE;
    }

    float coordinateX, coordinateY, coordinateZ;
    std::string Character;

    while (!FileStream.eof())
    {
        FileStream >> Character;

        if (Character == "v")
        {
            FileStream >> coordinateX >> coordinateY >> coordinateZ;
            std::cout << "Loading in " << coordinateX << " " << coordinateY << " " << coordinateZ << std::endl;
            Vertices.push_back(coordinateX);
            Vertices.push_back(coordinateY);
            Vertices.push_back(coordinateZ);
        }

        else
        {
            std::cout << "Skipping " << Character << std::endl;
            continue;
        }
    }

    std::cout << "Loaded " << FileName << std::endl;

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    unsigned int VBO;
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(float) * Vertices.size(), &Vertices.front(), GL_STATIC_DRAW);

    unsigned int VAO;
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

    const char* Vertex_Shader =
        "#version 330\n"
        "in vec3 vp;"
        "void main () {"
        "  gl_Position = vec4 (vp, 1.0);"
        "}";

    const char* Fragment_Shader =
        "#version 330\n"
        "out vec4 frag_colour;"
        "void main () {"
        "  frag_colour = vec4 (0.5, 0.0, 0.5, 1.0);"
        "}";

    unsigned int VertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(VertexShader, 1, &Vertex_Shader, NULL);
    glCompileShader(VertexShader);

    unsigned int FragmentShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(FragmentShader, 1, &Fragment_Shader, NULL);
    glCompileShader(FragmentShader);

    unsigned int Shader_Program = glCreateProgram();
    glAttachShader(Shader_Program, FragmentShader);
    glAttachShader(Shader_Program, VertexShader);
    glLinkProgram(Shader_Program);

    while (!glfwWindowShouldClose(Window))
    {

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glUseProgram(Shader_Program);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, Vertices.size());

        glfwPollEvents();
        glfwSwapBuffers(Window);
    }

    return EXIT_SUCCESS;
}

而加载的文件如下：

v 0.0 0.5 0.0
v 0.5 -0.5 0.0
v -0.5 -0.5 0.0

Answer 1

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

const char* Vertex_Shader =
    "#version 330\n"
    "in vec3 vp;"
    "void main () {"
    "  gl_Position = vec4 (vp, 1.0);"
    "}";

不保证属性将按声明顺序分配属性槽。

您需要告诉 OpenGL（通过 a location qualifier 或 glBindAttribLocation() pre-link）将它放在哪里或询问（glGetAttribLocation() post-link）它放在哪里。

Answer 2

这段代码至少有3个问题：

1. 它创建了两个顶点着色器对象，并且没有片段着色器对象。替换：

   unsigned int FragmentShader = glCreateShader(GL_VERTEX_SHADER);
   

   作者：

   unsigned int FragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
   

2. glDrawArrays() 的第三个参数必须是顶点数，而此代码传入坐标总数。由于此处使用每个顶点 3 个坐标，因此将调用更改为：

   glDrawArrays(GL_TRIANGLES, 0, Vertices.size() / 3);
   

3. 没有指定顶点属性的位置。这可能会因“意外”而起作用，特别是只要只有一个属性。但是指定位置要安全得多。最简单的方法是将位置添加到顶点着色器vp 的声明中：

   "layout(location = 0) in vec3 vp;"
   

Answer 3

1. 你绑定GL_ARRAY_BUFFER错了
2. 您的着色器创建中有错误
3. 您的着色器错误

1) 只需绑定（并创建）您的GL_ARRAY_BUFFER在您的glBindVertexArray 调用之后。

2）正如在另一个答案中已经说过的，您的片段着色器创建是错误的，应该是：unsigned int FragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

3) 您理所当然地认为您将在着色器中获得正确的属性，这是不好的做法。你应该是明确的并且有一个类似于这样的布局：layout(location = X) in vec3 myVec;

---

也作为一些提示：

无需在循环中重新绑定您的 VAO，只需在 while(!glfwWindowShouldClose(Window)) 之前绑定即可。您的着色器程序也是如此。

您应该检查您的着色器是否正确编译以及您的程序是否正确链接！分别查看glGetShaderiv、glGetProgramiv 和GL_COMPILE_STATUS 和GL_LINK_STATUS；和glGetShaderInfoLog 和glGetProgramInfoLog，如果您没有获得GL_TRUE 的任何一种状态。

这将为您提供一条消息，告诉您在编译/链接时遇到的确切问题，以便您可以轻松调试着色器代码而无需猜测。