GLfloat vertices[] = {
    -1.0f, -1.0f,  1.0f,
     1.0f, -1.0f,  1.0f,
    -1.0f,  1.0f,  1.0f,
     1.0f,  1.0f,  1.0f,
    -1.0f, -1.0f, -1.0f,
     1.0f, -1.0f, -1.0f,
     1.0f,  1.0f, -1.0f,
    -1.0f,  1.0f, -1.0f,
};

    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
    glClearDepth( 1.0f );
    glEnable( GL_DEPTH_TEST );
    glDepthFunc( GL_LEQUAL );

    glViewport( 0, 0, static_cast<GLsizei>(width), static_cast<GLsizei>(height) ); // 640 x 480

    glUseProgram(prog) // already successfully compiled and linked
    glUniform1f(glGetAttribLocation(prog, "height"), 2.0f);
    glUniform1f(glGetAttribLocation(prog, "aspect"), 4.0f/3.0f);
    glUniform1f(glGetAttribLocation(prog, "zNear"), -2.0f);
    glUniform1f(glGetAttribLocation(prog, "zFar"), 2.0f);
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    GLuint name = glGetAttribLocation(prog, "position");
    glEnableVertexAttribArray(name);
    glVertexAttribPointer(name, 3, GL_FLOAT, GL_FALSE, 0, reinterpret_cast<void*>(0));