I am trying to create a text class witch has its own vertex array, vertex buffer, index buffer and draw them on a function call. It looks like so:

class Text {
private:
    std::string m_FontFilePath;
    std::string m_Text;
    Texture* m_FontTexture;

    VertexBuffer* m_Vbo;
    IndexBuffer* m_Ibo;
    VertexArray* m_Va;
    float* m_TextPos;
    unsigned int* m_Index;
    unsigned int m_IndexCount;
public:
    Text(std::string fontFilePath, std::string text, float posX, float posY);
    ~Text();

    void drawText();
};

void Text::drawText()
{
    m_Va->Bind();
    glDrawElements(GL_TRIANGLES, m_IndexCount, GL_UNSIGNED_INT, nullptr);
}

This is the constructor that creates everything:

Text::Text(std::string fontFilePath, std::string text, float posX, float posY)
    : m_FontFilePath(fontFilePath), m_Text(text)
{
    VertexArray va2;
    va2.Bind();

    m_TextPos = new float[m_Text.size() * 24];

    std::cout << posX << " " << posY<<"\n";
    
    float unitH = 0.1f, unitW = 0.1f;
    int countNow = 0;
    for (auto letter : m_Text)
    {
        addLetter(m_TextPos, {
            // posX          posY poZ       TextureCoord, TextureIndex
               posX,          posY, 0,          0.0f, 0.0f, 0.0f,
               posX   unitW, posY,  0,          1.0f, 0.0f, 0.0f,
               posX   unitW, posY   unitH, 0,  1.0f, 1.0f, 0.0f,
               posX,          posY   unitH, 0,  0.0f, 1.0f, 0.0f
            }, countNow);

        posX  = unitW;
        countNow  = 24;
    }
    // this creates a square for every letter of the word    

    VertexBuffer vb2(m_TextPos, sizeof(float) * 24 * m_Text.size());
    VertexBufferLayout vbl2;
    vbl2.Push<float>(3);
    vbl2.Push<float>(2);
    vbl2.Push<float>(1);
    va2.AddBuffer(vb2, vbl2);
    
    m_Index = new unsigned int[m_Text.size() * 6];
    for (int i = 0; i < m_Text.size(); i  ) {
        m_Index[i * 6   0] = i * 4   0;
        m_Index[i * 6   1] = i * 4   1;
        m_Index[i * 6   2] = i * 4   2;
        m_Index[i * 6   3] = i * 4   2;
        m_Index[i * 6   4] = i * 4   3;
        m_Index[i * 6   5] = i * 4   0;
    }
    // this creates the m_Index array
    IndexBuffer ibo2(m_Index, m_Text.size() * 6);

    m_Vbo = &vb2;
    m_Ibo = &ibo2;
    m_Va = &va2;
    m_IndexCount = 6 * m_Text.size();

    std::cout << "INDEXES:\n";
    for (int i = 0; i < m_Text.size() * 6; i  ) {
        std::cout << m_Index[i] << " ";
        if ((i   1) % 6 == 0) std::cout << "\n";
    }
    std::cout << "\nINSIDE VBO:\n";
    for (int i = 0; i < 24 * m_Text.size(); i  ) {
        std::cout << m_TextPos[i] << " ";
        if ((i   1) % 6 == 0)std::cout << "\n";
    }

    va2.Unbind();
}

The IndexBuffer and VertexBuffer have the right data in them(I checked both). If I take all the data from this class and move it in main.cpp and draw it there it works fine witch I find weird. The main loop looks like so:

Text test(filePath, "randomText", 0.1f, 0.1f);
while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
        
        // va = vertex array I created above this while loop, contains
        va.Bind(); // 2 squares, it draws good
        glDrawElements(GL_TRIANGLES, 12, GL_UNSIGNED_INT, nullptr);

        test.drawText(); // nothing draws on screen

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

CodePudding user response：

Your buffers objects are local in scope of Text::Text. The attributes are dangling pointers. You have to create dynamic objects. Remove the local variables va2, vb2 and ibo2 but allocate dynamic memory and create the objects with the new operator:

Text::Text(std::string fontFilePath, std::string text, float posX, float posY)
    : m_FontFilePath(fontFilePath), m_Text(text)
{
    m_Va = new VertexArray(); 
    m_Va->Bind();

    // [...]

    m_Vbo = new VertexBuffer(m_TextPos, sizeof(float) * 24 * m_Text.size());
    
    // [...]

    m_Ibo = new IndexBuffer(m_Index, m_Text.size() * 6);
    
    // [...]
}

Don't forget to delete the objects in the class's destructor.