c++ - 如何在Ubuntu 18.04.3上将 “upgrade”转换为OpenGL 3.3

我已经阅读了很多关于此的内容，但还无法解决任何问题。我正在尝试使用OpenGL3绘制彩色三角形，但出现以下错误:

引发'std::runtime_error'实例之后终止调用what():顶点着色器的编译错误(来自文件./TP1/shaders/triangle.vs.glsl):0:1(10):错误:GLSL 3.30不支持。 支持的版本是:1.10、1.20、1.30、1.00 ES，3.00 ES，3.10 ES和3.20 ES

当我运行 glxinfo | grep -i opengl 我得到:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 6000 (Broadwell GT3)
OpenGL core profile version string: 3.3 (Core Profile) Mesa 19.0.8
OpenGL core profile shading language version string: 4.50
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL version string: 3.0 Mesa 19.0.8
OpenGL shading language version string: 4.50
OpenGL context flags: (none)
OpenGL profile mask: compatibility profile
OpenGL extensions:
OpenGL ES profile version string:
OpenGL ES 3.1 Mesa 19.0.8
OpenGL ES profile shading language version string:
OpenGL ES GLSL ES 3.10
OpenGL ES profile extensions:

我尝试了导出MESA_GL_VERSION_OVERRIDE = 3.3 ，这使我能够执行代码，但是我只得到了一个怪异的三角形，而不是漂亮的等边多色三角形。
这是我的完整代码:

#include <glimac/SDLWindowManager.hpp>
#include <GL/glew.h>
#include <iostream>
#include <glimac/Program.hpp>
#include <glimac/FilePath.hpp>

using namespace glimac;

int main(int argc, char** argv) {

    // Initialize SDL and open a window
    SDLWindowManager windowManager(800, 600, "GLImac");

    // Initialize glew for OpenGL3+ support
    GLenum glewInitError = glewInit();
    if(GLEW_OK != glewInitError) {
        std::cerr << glewGetErrorString(glewInitError) << std::endl;
        return EXIT_FAILURE;
    }

    std::cout << "OpenGL Version : " << glGetString(GL_VERSION) << std::endl;
    std::cout << "GLEW Version : " << glewGetString(GLEW_VERSION) << std::endl;

    //load shaders and tell OpenGL to use them
    FilePath applicationPath(argv[0]);
    Program program = loadProgram(applicationPath.dirPath() + "shaders/triangle.vs.glsl",
                                    applicationPath.dirPath() + "shaders/triangle.fs.glsl");
    program.use();

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    //triangle data
    GLfloat vertices[] = { -0.5f, -0.5f, 1.f, 0.f, 0.f, //2 coordinates + 1 0 0 color
                         0.5f, -0.5f, 0.f, 1.f, 0.f,
                         0.0f, 0.5f, 0.f, 0.f, 1.f };

    glBufferData(GL_ARRAY_BUFFER, (15*(sizeof(float))), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    const GLuint VERTEX_ATTR_POSITION = 3;
    const GLuint VERTEX_ATTR_COLOR = 8;
    glEnableVertexAttribArray(VERTEX_ATTR_POSITION);
    glEnableVertexAttribArray(VERTEX_ATTR_COLOR);

    const GLvoid* bouche;
    glVertexAttribPointer(VERTEX_ATTR_POSITION, 2, GL_FLOAT, GL_FALSE, (0*sizeof(GL_FLOAT)), bouche);
    glVertexAttribPointer(VERTEX_ATTR_COLOR, 3, GL_FLOAT, GL_FALSE, (2*sizeof(GL_FLOAT)), bouche);

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glVertexAttribPointer(VERTEX_ATTR_POSITION, 2, GL_FLOAT, GL_FALSE, (2*sizeof(GL_FLOAT)), 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glBindVertexArray(0);


    // Application loop:
    bool done = false;
    while(!done) {
        // Event loop:
        SDL_Event e;
        while(windowManager.pollEvent(e)) {
            if(e.type == SDL_QUIT) {
                done = true; // Leave the loop after this iteration
            }
        }

        //clean window
        glClear(GL_COLOR_BUFFER_BIT);
        glBindVertexArray(vao);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glBindVertexArray(0);

        // Update the display
        windowManager.swapBuffers();
    }

    //liberate allocated memory on GPU (the vbo and vao)
    glDeleteBuffers(1, &vbo);
    glDeleteVertexArrays(1, &vao);
    return EXIT_SUCCESS;
}

最佳答案

使用glew时，请通过glewExperimental = GL_TRUE;启用其他扩展名。参见GLEW documentation，其中说:

glewExperimental = GL_TRUE;
GLenum glewInitError = glewInit();
if(GLEW_OK != glewInitError) {
    std::cerr << glewGetErrorString(glewInitError) << std::endl;
    return EXIT_FAILURE;
}

当命名缓冲区对象绑定(bind)到目标GL_ARRAY_BUFFER时， glVertexAttribPointer 的最后一个参数被视为该缓冲区的字节偏移量。
调用 glVertexAttribPointer 时，顶点数组规范将存储在当前绑定(bind)的顶点数组对象的状态 vector 中。当前绑定(bind)到目标GL_ARRAY_BUFFER的缓冲区与属性关联，并且对象的名称(值)存储在VAO的状态 vector 中。
还要注意，glVertexAttribPointer的第5个参数(跨度)指定了连续通用顶点属性之间的字节偏移。

这意味着在调用glVertexAttribPointer之前，必须绑定(bind)Vertex Array Object和Vertex Buffer Object。
stride参数必须为5*sizeof(Glfloat)，因为顶点属性由5个GLfloat值(x，y，r，g，b)组成。VERTEX_ATTR_POSITION的偏移量是0，而VERTEX_ATTR_COLOR的偏移量是2*sizeof(GLfloat)，因为(r，g b)在(x，y)之后。请注意，GL_FLOAT是枚举器常量，而不是数据类型，因此2*sizeof(GL_FLOAT)不会执行您期望的操作。

//triangle data
GLfloat vertices[] = { -0.5f, -0.5f, 1.f, 0.f, 0.f, //2 coordinates + 1 0 0 color
                        0.5f, -0.5f, 0.f, 1.f, 0.f,
                        0.0f, 0.5f,  0.f, 0.f, 1.f };

// create vertex buffer object
GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

// vertex array object
 GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

// specify the array of generic vertex attribute data
glBindBuffer(GL_ARRAY_BUFFER, vbo); // if "vbo" is still bound then that would not be necessary
glVertexAttribPointer(VERTEX_ATTR_POSITION, 2, GL_FLOAT, GL_FALSE, 5*sizeof(GLfloat), nullptr);
glVertexAttribPointer(VERTEX_ATTR_COLOR,    3, GL_FLOAT, GL_FALSE, 5*sizeof(GLfloat), 2*sizeof(GLfloat));

glEnableVertexAttribArray(VERTEX_ATTR_POSITION);
glEnableVertexAttribArray(VERTEX_ATTR_COLOR);

// the following is not necessary, you can let them bound
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);

确保顶点属性索引正确:

const GLuint VERTEX_ATTR_POSITION = 3;
const GLuint VERTEX_ATTR_COLOR = 8;

3和8是可能的，但看起来很奇怪。这不应该是属性的资源索引，该属性索引可以由Layout qualifier设置或可以在链接程序后由 glGetAttribLocation 获取。

顺便说一下，等边三角形的坐标为:

GLfloat vertices[] = {
     x        y      r    g    b
    -0.866f, -0.5f,  1.f, 0.f, 0.f,
     0.866f, -0.5f,  0.f, 1.f, 0.f,
     0.0f,    1.0f,  0.f, 0.f, 1.f };