无法获得简单的 2D 着色器以在 C++ openGL 中绘制红色三角形（无编译器错误）

Posted 2023-02-16

【中文标题】无法获得简单的 2D 着色器以在 C++ openGL 中绘制红色三角形（无编译器错误）

【英文标题】：Unable to get trivial 2D shader to draw red triangle in C++ openGL (No compiler errors)

【发布时间】：2020-04-26 14:32:34

【问题描述】：

我使用了 openGL、GLEW 和 GLFW3。在 openGl 3.0 mesa 中，使用了默认着色器并绘制了一个白色三角形。在 4.2 中，屏幕保持黑色。未生成任何错误消息。

问题不是由于将片段着色器错误标记为顶点着色器，反之亦然。

该程序包含3个功能：

(1) compileShader，它应该将shader类型和源代码作为std::string，并返回一个带有编译代码的shader ID。

(2) createProgram，获取顶点着色器和片段着色器的源代码，并返回一个程序ID，着色器已编译并附加。

(3) 和 main，其中两个着色器源代码都定义为字符串。

对不起，谢谢。

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

#include <iostream>
#include <string>

static unsigned int compileShader(unsigned int type, std::string const& sourceCode)
    unsigned int shaderId = glCreateShader(type);
    const char* source = sourceCode.c_str();
    glShaderSource(shaderId, 1, &source, nullptr);
    glCompileShader(shaderId);

    int result;
    glGetShaderiv(shaderId, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE)

        if (type == GL_FRAGMENT_SHADER) std::cout<<"Fragment\n";
        else std::cout<<"Vertex";
        std::cout<<"SHADER COMPILATION FAILED!"<<std::endl;
        int logLength;
        glGetShaderiv(shaderId, GL_INFO_LOG_LENGTH, &logLength);
        char* infoLog = new char[logLength];
        glGetShaderInfoLog(shaderId, logLength, NULL, infoLog);
        std::cout<<infoLog<<std::endl;
        delete[] infoLog;

        glDeleteShader(shaderId);
        return 0;
    

    return shaderId;


static unsigned int createProgram(std::string const& vertexCode, std::string const& fragmentCode)
    unsigned int vsId = compileShader(GL_VERTEX_SHADER, vertexCode);
    unsigned int fsId = compileShader(GL_FRAGMENT_SHADER, fragmentCode);

    unsigned int programId = glCreateProgram();
    glAttachShader(programId, vsId);
    glAttachShader(programId, fsId);
    glLinkProgram(programId);
    glValidateProgram(programId);

    glDeleteShader(vsId);
    glDeleteShader(fsId);
    return programId;


int main()


    GLFWwindow* window;

    if (!glfwInit())
    
        std::cout<<"GLFW initialization failed";
        return -1;
    

    ///switches to opengl 4.2!
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
    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);
    glewInit();

    std::cout << "OpenGL " << glGetString(GL_VERSION) << "\n" << std::endl;
    float positions[6] = 
        0.5f, 0.5f,
        -0.5f, 0.5f,
        0.0f, 0.0f
    ;

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

    glEnableVertexAttribArray(0);                                        //enables the xy attrib of position
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2*sizeof(float), 0); //specifies layout of xy attrib

    std::string vertexSource =   R"(
#version 330 core
layout(location=0) in vec4 position;

void main()
    gl_Position = position;

)";
    std::string fragmentSource = R"(
#version 330 core

layout(location=0) out vec4 color;

void main()
    color = vec4(1.0, 0.0, 0.0, 1.0);

)";

    unsigned int programId = createProgram(vertexSource, fragmentSource);
    glUseProgram(programId);

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

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

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

    glfwTerminate();
    return 0;

【参考方案1】：

问题不在于着色器程序，而是您使用的是核心配置文件OpenGL Context (GLFW_OPENGL_CORE_PROFILE)。因此，您必须创建一个名为Vertex Array Object。默认 VAO (0) 在核心配置文件上下文中无效。

glGenVertexArrays生成顶点数组对象名，glBindVertexArray创建并绑定对象：

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

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

glEnableVertexAttribArray(0);                                        //enables the xy attrib of position
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2*sizeof(float), 0); //specifies layout of xy attrib

【讨论】：

谢谢，它成功了。毫不奇怪，我是 OpenGL 的初学者，所以我还没有遇到顶点数组对象。你有什么好的教程推荐吗？

@VivekPanchagnula 谢谢。别客气。我推荐LearnOpenGL