Problem rendering any sf::Drawable*

[nullByte]

Ive been trying to work out the best way to manage the drawing of all sprites, text or any sf::Drawable for that matter within my game.

I wanted all the drawables to be displayed stored in a vector so that I can draw them all at once within the main function instead of passing around a reference to the RenderWindow.

To solve this I created a vector of sf::Drawable pointers so that I can fill the vector with the any object that is derived from sf::Drawable

Here is my solution:

main.cpp

#include <vector>
#include "title_screen.h"

int main()
{
    sf::RenderWindow window(...);
    std::vector<sf::Drawable*> drawBuffer;

    TitleScreen titleScreen(window.getSize());
    titleScreen.pushDrawablesToVector(drawBuffer);

    // Event Handler
    while (window.isOpen) {...}

    window.clear(sf::Color::White);
    for (std::vector<sf::Drawable*>::iterator i = drawBuffer.begin(); i < drawBuffer.end(); i++)
    {
        window.draw(**i);
    }
    window.display();
}
 

title_screen.h

#include <vector>
#include <SFML/Graphics.hpp>

class TitleScreen
{
    sf::Text title;
    sf::Text newGame;

public:
    // Constructor which sets text position using winSize and strings
    TitleScreen(sf::Vector2u winSize) {...}
   
    void pushDrawablesToVector(std::vector<sf::Drawable*> &dB)
    {
        dB.push_back(&title);
        dB.push_back(&newGame);
    }
};
 

The code compiles and runs fine, the problem is I get a black white screen without any text.

Im assuming this has something to do with the size of sf::Drawable* vs sf::Text* (and sf::Text private member data not inherited from sf::Drawable).

Any ideas or suggestions?
Thanks in advance

[eXpl0it3r]

You could debug your application to see what goes wrong, if you don't know how to debug things, learn it, it's the most important tool of adeveloper!
Do you set some strings to the sf::Text in your TitleScreen class?
Does the for-loop ever get executed?

[Laurent]

Im assuming this has something to do with the size of sf::Drawable* vs sf::Text* (and sf::Text private member data not inherited from sf::Drawable).

All pointers have the same size (a pointer is a 32 or 64-bit memory address, regardless of what it points to). This would be a problem if you stored sf::Drawable instances and not pointers; in this case the problem is called slicing (you only keep the sf::Drawable members and lose all the derived class' data). But when you copy pointers, you never lose anything.

So there's definitely something wrong in the code that you don't show.

I wanted all the drawables to be displayed stored in a vector so that I can draw them all at once within the main function instead of passing around a reference to the RenderWindow.

What you're trying to avoid would be a much better design. A class should implement services ("draw yourself"), not provide data ("what drawables do you want to draw?"). This is more abstract and intuitive.

By the way, this is a code that works:

#include <SFML/Graphics.hpp>
#include <vector>

int main()
{
    sf::RenderWindow window(sf::VideoMode(640, 480), "SFML test");

    sf::Font font;
    font.loadFromFile("C:/Windows/Fonts/Arial.ttf");
    sf::Text text1("hello", font);
    sf::Text text2("world", font);
    text2.move(0, 50);

    std::vector<sf::Drawable*> drawables;
    drawables.push_back(&text1);
    drawables.push_back(&text2);

    while (window.isOpen())
    {
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
                window.close();
        }

        window.clear();
        for (std::vector<sf::Drawable*>::const_iterator it = drawables.begin(); it != drawables.end(); ++it)
            window.draw(**it);
        window.display();
    }

    return 0;
}

[nullByte]

Thanks for the advice.

It turns out the problem was I never set the text color to black (I guess it defaults to white and because my clear color is white I couldn't see it, duh  )

Im glad I got it working, and thanks for the information from Laurent about slicing (it helped me understand parts of my code better).
I am going to change my draw code back to what it was before by passing a RenderWindow reference to a member function of titleScreen in order to draw the text as Laurent suggested.