现代 OpenGL MacOS 只有黑屏

Question

我正在关注 C++ 中的 OpenGL 教程（Youtube 上的 The Cherno）。我有以下代码，但无论我尝试什么，我都无法绘制三角形。创建了一个窗口，我没有收到任何错误等，我什至可以使用 glClearColor 更改背景颜色。但没有三角形！

有关信息，我通过 Homebrew 安装了 GLFW/GLEW，并且我正在使用 CLion。

CMakeList.txt

cmake_minimum_required(VERSION 3.3)
project(Lib_Test)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -framework Cocoa -framework OpenGL -framework IOKit")

set(SOURCE_FILES src/main.cpp CMakeLists.txt)

# add extra include directories
include_directories(/usr/local/include)

# add extra lib directories
link_directories(/usr/local/lib)

add_executable(Lib_Test main.cpp)
target_link_libraries(Lib_Test glfw)
target_link_libraries(Lib_Test glew)
find_package (GLM REQUIRED)
include_directories(include)

ma​​in.cpp

#include <stdio.h>
#include <iostream>
#include <GL/glew.h>
#include <GLFW/glfw3.h>


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") << 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(){

    // Initialise GLFW
    if( !glfwInit() )
    {
        fprintf( stderr, "Failed to initialize GLFW\n" );
        return -1;
    }

    glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); // We want OpenGL 3.3
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window; // (In the accompanying source code, this variable is global for simplicity)
    window = glfwCreateWindow( 640, 480, "My App", NULL, NULL);
    if( window == NULL ){
        fprintf( stderr, "Failed to open GLFW window.\n" );
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    glewExperimental=true; // Needed in core profile
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        return -1;
    }

    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";
        "\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) )
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0 ,3);
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

Answer 1

您必须在核心上下文中创建和绑定 VAO，它不像在兼容性上下文中那样是可选的。

Answer 2

除了 genpflaut 的回答，我提到你的着色器代码根本无法编译。

您必须删除字符串文字之间的分号，并且在color = vec4(1.0, 0.0, 0.0, 1.0) 之后缺少分号。

你的代码应该是这样的：

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"
    "\n"
    "void main()\n"
    "{\n"
    "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
    "}\n";

如果您生成并绑定顶点数组对象，则在生成缓冲区对象之前，您的代码将正常运行。

在glBindBuffer(GL_ARRAY_BUFFER, buffer)之前添加以下行：

unsigned int vao;
glGenVertexArrays( 1, &vao );
glBindVertexArray( vao ); 

进一步看OpenGL 3.3 core profile specification, E.2.2 Removed Features, page 344

默认的顶点数组对象（名称为零）也已弃用。在没有绑定缓冲区对象或没有绑定顶点数组对象时调用VertexAttribPointer会产生一个INVALID_OPERATION错误，当没有绑定顶点数组对象时调用任何数组绘制命令也会产生错误。