c++ - OpenGL 不会绘制三角形，遵循精确的格式

Question

我能够创建一个窗口并且一切正常，但是当我尝试制作一个三角形时，它不会显示。

我已经创建了一个缓冲区并绑定(bind)它，还制作了我的着色器，所以我不明白为什么它不起作用。

我正在使用 MacOSX 和 Xcode。

#include <iostream>

using namespace std;
//GLEW
#define GLEW_STATIC
#include <GL/glew.h>

//GLFW
#include <GLFW/glfw3.h>

const GLint WIDTH = 800, HEIGHT = 600;


static unsigned int CompileShader(unsigned int type, const std::string& source)
{
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);

    if (result == GL_FALSE)
    {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile" << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" <<std::endl;
        std::cout << message << std::endl;
        glDeleteShader(id);
        return 0;
    }

    return id;
}

static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader)
{
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);


    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;


}

int main(void)
{
    //glfwInit();


    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint( GLFW_RESIZABLE, GL_FALSE );

    GLFWwindow * window;

    if (!glfwInit())
        return -1;

    window = glfwCreateWindow( WIDTH, HEIGHT, "Learn OpenGL", NULL, NULL);

    int screenWidth, screenHeight;
    glfwGetFramebufferSize( window, &screenWidth, & screenHeight);

    if (!window)
    {
        cout << "Failed to create" << endl;
        glfwTerminate();

        return -1;
    }

    glfwMakeContextCurrent( window );

    glewExperimental = GL_TRUE;

    if ( glewInit() != GLEW_OK )
    {
        cout << "Failed to Initialize Glew" << endl;

        return -1;
    }

    glViewport ( 0, 0, screenWidth, screenHeight);

    //vertex buffer

    float positions[6] = {
       -0.5f, -0.5f,
        0.0f, 0.5f,
        0.5f, -0.5f
    };


    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, (6 * sizeof(float)), positions, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, (sizeof(float)*2), 0);


    std::string vertexShader =
    "#version 330 core\n"
    "\n"
    "layout(location = 0) in vec4 position;\n"
    "\n"
    "void main()\n"
    "{\n"
    "   gl_Position = position;\n"
    "}\n";

    std::string fragmentShader =
    "#version 330 core\n"
    "\n"
    "   layout(location = 0) out vec4 color;"
    "\n"
    "void main()\n"
    "{\n"
    "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
    "}\n";

    unsigned int shader = CreateShader(vertexShader, fragmentShader);
    glUseProgram(shader);

    while ( !glfwWindowShouldClose ( window ))
    {

        glClearColor(0.2f, 0.3F, 0.3, 1.0f);
        glClear( GL_COLOR_BUFFER_BIT );


        glDrawArrays(GL_TRIANGLES, 0, 3);


        glfwSwapBuffers( window );
        glfwPollEvents();

    }

    glfwTerminate( );
    return 0;

}

Answer 1

几件事:

1. 在调用 glfwWindowHint() 之前调用 glfwInit()。否则它不会有任何效果，你会(可能)以 a Compatibility context instead of the Core context 结束。你在问。

   如果你设置an error callback :

   int main(void)
   {
       glfwSetErrorCallback( []( int, const char* str )
       {
           std::cerr << "GLFW error: " << str << std::endl;
       });
   
       glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3);
       glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3);
       glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
       glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
       glfwWindowHint( GLFW_RESIZABLE, GL_FALSE );
   
       if (!glfwInit())
           return -1;
   ...
   

   ...您可以看到调用 (most) 导致的 GLFW 错误流glfwInit() 之前的 GLFW 函数:

   GLFW error: The GLFW library is not initialized
   GLFW error: The GLFW library is not initialized
   GLFW error: The GLFW library is not initialized
   GLFW error: The GLFW library is not initialized
   GLFW error: The GLFW library is not initialized
   

2. Vertex Array Objects (VAOs)在核心上下文中不是可选的。

   在尝试启用/设置顶点属性和绘图之前创建并绑定(bind)一个 VAO:

   ...
   GLuint vao = 0;
   glGenVertexArrays( 1, &vao );
   glBindVertexArray( vao );
   
   glEnableVertexAttribArray(0);
   ...
   

一起:

#include <iostream>

using namespace std;
//GLEW
#define GLEW_STATIC
#include <GL/glew.h>

//GLFW
#include <GLFW/glfw3.h>

const GLint WIDTH = 800, HEIGHT = 600;


static unsigned int CompileShader(unsigned int type, const std::string& source)
{
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);

    if (result == GL_FALSE)
    {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile" << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" <<std::endl;
        std::cout << message << std::endl;
        glDeleteShader(id);
        return 0;
    }

    return id;
}

static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader)
{
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);


    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;


}

int main(void)
{
    if (!glfwInit())
        return -1;

    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint( GLFW_RESIZABLE, GL_FALSE );

    GLFWwindow * window;
    window = glfwCreateWindow( WIDTH, HEIGHT, "Learn OpenGL", NULL, NULL);

    int screenWidth, screenHeight;
    glfwGetFramebufferSize( window, &screenWidth, & screenHeight);

    if (!window)
    {
        cout << "Failed to create" << endl;
        glfwTerminate();

        return -1;
    }

    glfwMakeContextCurrent( window );

    glewExperimental = GL_TRUE;

    if ( glewInit() != GLEW_OK )
    {
        cout << "Failed to Initialize Glew" << endl;

        return -1;
    }

    glViewport ( 0, 0, screenWidth, screenHeight);

    //vertex buffer

    float positions[6] = {
       -0.5f, -0.5f,
        0.0f, 0.5f,
        0.5f, -0.5f
    };


    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, (6 * sizeof(float)), positions, GL_STATIC_DRAW);

    GLuint vao = 0;
    glGenVertexArrays( 1, &vao );
    glBindVertexArray( vao );

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, (sizeof(float)*2), 0);


    std::string vertexShader =
    "#version 330 core\n"
    "\n"
    "layout(location = 0) in vec4 position;\n"
    "\n"
    "void main()\n"
    "{\n"
    "   gl_Position = position;\n"
    "}\n";

    std::string fragmentShader =
    "#version 330 core\n"
    "\n"
    "   layout(location = 0) out vec4 color;"
    "\n"
    "void main()\n"
    "{\n"
    "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
    "}\n";

    unsigned int shader = CreateShader(vertexShader, fragmentShader);
    glUseProgram(shader);

    while ( !glfwWindowShouldClose ( window ))
    {

        glClearColor(0.2f, 0.3F, 0.3, 1.0f);
        glClear( GL_COLOR_BUFFER_BIT );


        glDrawArrays(GL_TRIANGLES, 0, 3);


        glfwSwapBuffers( window );
        glfwPollEvents();

    }

    glfwTerminate( );
    return 0;
}