OpenGL三角形未渲染

问题描述

当我遇到一个没有得到预期结果的问题时，我正在学习 OpenGL 教程。我期待在窗口中看到一个三角形，但结果却是一个空窗口。我对代码进行了许多更改以帮助它在我的机器上运行，但没有解决问题。其中一些更改包括添加：

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR,3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MInor,3);
glfwWindowHint(GLFW_OPENGL_PROFILE,GLFW_OPENGL_CORE_PROFILE);

为了请求核心配置文件上下文，使用 VBO 添加 VAO，我什至从教程中下载了代码，但无济于事。有人知道解决我的问题的方法吗？

代码：

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

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)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;
        
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR,3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MInor,3);
    glfwWindowHint(GLFW_OPENGL_PROFILE,GLFW_OPENGL_CORE_PROFILE);

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640,480,"Hello World",NULL,NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context  current */
    glfwMakeContextCurrent(window);
    
    if(glewInit() != GLEW_OK){
        std::cout << "REEEEEEEEEEE" << std::endl;
    }
    
    float vertices[6] = {
        -0.5f,-0.5f,0.0f,0.5f,-0.5f
    };
    
    unsigned int buf;
    glGenBuffers(1,&buf);
    glBindBuffer(GL_ARRAY_BUFFER,buf);
    glBufferData(GL_ARRAY_BUFFER,6 * sizeof(float),vertices,GL_STATIC_DRAW);
    
    glEnabLevertexAttribArray(0);
    glVertexAttribPointer(0,2,GL_FLOAT,GL_FALSE,sizeof(float) * 2,0);
    
    std::string vertexshader = 
    "#version 330 core\n"
    "\n"
    "in vec4 position;\n"
    "out vec4 color;\n"
    "\n"
    "void main(){\n"
    "   gl_Position = position;\n"
    "   color = position;\n"
    "}\n";
    
    std::string fragmentshader = 
    "#version 330 core\n"
    "\n"
    "in vec4 in_color;\n"
    "out vec4 color;\n"
    "\n"
    "void main(){\n"
    "   color = in_color;\n"
    "}\n";
    
    unsigned int shader = CreateShader(vertexshader,fragmentshader);
    gluseProgram(shader);
    
    glClearColor(0.33f,0.33f,1.0f);
    
    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES,3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

CMakeLists:

cmake_minimum_required (VERSION 3.5)

if(POLICY CMP0072)
    cmake_policy(SET CMP0072 NEW)
else(NOT POLICY CMP0072)
    message(STATUS "Error")
endif(POLICY CMP0072)

project (opengl-learning)

find_package(PkgConfig required)
pkg_search_module(GLFW required glfw3)
include_directories(${GLFW_INCLUDE_Dirs} ${OPENGL_INCLUDE_DIR})

set (GCC_COVERAGE_LINK_FLAGS "-lglfw3 -pthread -ldl -lglu -lGL -lrt -lXrandr -lXxf86vm -lXi -lXinerama -lX11 -lGLEW -lglu -lGL")

add_deFinitions(${GCC_COVERAGE_COMPILE_FLAGS})

set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++14")
set (source_dir "${PROJECT_SOURCE_DIR}/src/")

file (GLOB source_files "${source_dir}/*.cpp")

add_executable (opengl-learning ${source_files})

find_package(OpenGL required)
find_package(GLEW required)

target_link_libraries(opengl-learning ${GLFW_LIBRARIES} ${GLEW_LIBRARIES} ${OPENGL_LIBRARIES})

版本（请求核心配置文件）

glGetString(GL_VERSION) >> 3.3 (Core Profile) Mesa 18.3.6
glGetString(GL_SHADING_LANGUAGE_VERSION) >> 3.30

操作系统：Linux Debian 10

如果需要任何额外信息，请随时询问。

解决方法

当您使用核心配置文件 OpenGL Context 时，您必须创建一个 Vertex Array Object：

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

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

默认的顶点数组对象 (0) 仅在使用兼容性配置文件 OpenGL 上下文时才有效：

glfwWindowHint(GLFW_OPENGL_PROFILE,GLFW_OPENGL_COMPAT_PROFILE);

我推荐阅读Vertex Specification。