"A reference to a non-static member must be relative to the specific object" when calling method of the c ++ class itself

I have a class where, within a non-static method, I want to make a call to another non-static call. However, in doing so, Visual Studio already gives this alert: "A reference to a non-static member must be relative to the specific object."

The point is that I'm calling the method from the same class, inside itself. In Java I do this without having to declare an instance of the class itself inside it (this would be a dumb redundancy).

How to solve this?

Here are my methods:

Method that is called:

//4- Cria os vértices e seu VBO e VAO. Define a cor a partir de um Uniform
void SceneManager::setupScene()
{



    GLuint VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);


    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // Position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);



    glBindVertexArray(0); 


    GLint colorLoc = glGetUniformLocation(shader->Program, "color");
    //assert(colorLoc > -1);
    glUseProgram(shader->Program);
    glUniform4f(colorLoc, 1.0f, 0.0, 0.2f, 1.0f);

Calling method:

    void SceneManager::key_callback(GLFWwindow * window, int key, int scancode, int action, int mode)
    {
        if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
            glfwSetWindowShouldClose(window, GL_TRUE);
        if (key >= 0 && key < 1024)
        {
            if (action == GLFW_PRESS)
                keys[key] = true;
            else if (action == GLFW_RELEASE)
                keys[key] = false;
        }

// O ERRO É SINALIZADO PELA IDE AQUI: QUANDO EU CHAMO O SETUPSCENE
        setupScene();
        switch (key)
        {
        case 65: //tecla A
        case 97: //tecla a
        vertices[0] = vertices[0]--;

            break;
        case 68: //tecla D
        case 100: //tecla d
            cout << "direita" << endl;
            break;
        case 83: //tecla S
        case 115: //tecla s
            cout << "baixo" << endl;
            break;
        case 87: //tecla W
        case 119: //tecla w
            cout << "cima" << endl;
        }


    }

In an earlier method, within the same class, setupScene () was already being called, without any error. Why in the other method accuse this error? ::

    *2 -INICIALIZA A JANELA GRÁFICA, INICIA O MÉTODO addShader() BUSCA OS DOIS SHADERS E SALVA NUMA VARIÁVEL,
    , INICIA O MÉTODO setupScene(), que cira o VBO e VAO dos vértices e define a cor via Uniform*/

void SceneManager::initializeGraphics()
    {
        // Init GLFW
        glfwInit();

        // Create a GLFWwindow object that we can use for GLFW's functions
        window = glfwCreateWindow(width, height, "Hello Transform", nullptr, nullptr);
        glfwMakeContextCurrent(window);

        // Set the required callback functions
        glfwSetKeyCallback(window, key_callback);

        //Setando a callback de redimensionamento da janela
        glfwSetWindowSizeCallback(window, resize);

        // Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions
        glewExperimental = GL_TRUE;

        // Initialize GLEW to setup the OpenGL Function pointers
        glewInit();

        // Build and compile our shader program
        addShader("../shaders/transformations.vs", "../shaders/transformations.frag");

        //setup the scene -- LEMBRANDO QUE A DESCRIÇÃO DE UMA CENA PODE VIR DE ARQUIVO(S) DE 
        // CONFIGURAÇÃO
        setupScene();

        resized = true; //para entrar no setup da câmera na 1a vez

    }