Would a buffer help me?

[BorisDieKlinge]

Hey.
I'm sorry but i couldn't think of a better subject.
Here is my Porblem:

Code: [Select]


#include <SFML/Graphics.hpp>

int main()
{
    sf::RenderWindow App(sf::VideoMode(800,600),"lala");
    App.UseVerticalSync(true);

    sf::Event Event;
    sf::Image Image;
    Image.LoadFromFile("E:/again_i_try_to/test/bin/Debug/x.bmp");

    sf::Sprite Sprite;
    Sprite.SetImage(Image);

    while(App.IsOpened())
    {
        while(App.GetEvent(Event))
        {
            if((Event.Type== sf::Event::KeyPressed) && (Event.Key.Code==sf::Key::Escape))
            App.Close();

            if(Event.Type==sf::Event::Closed)
            App.Close();
        }
        App.Clear(sf::Color(120,21,34));
        Sprite.SetPosition(Event.MouseMove.X,Event.MouseMove.Y);
        App.SetCursorPosition(100,100);

        App.Draw(Sprite);
        App.Display();
    }

    return EXIT_SUCCESS;
}


For some reason the cursor is moving around if you move your mouse. Thats not very surprising since I move it before I Set it back to (100,100). But why can I actually SEE this? Is there a way to fix this problem? Maybe a Buffersystem like in SDL?
I'm aware of the the fact, that I simly could delete the liene "Sprite.SetPosition(Event.MouseMove.X,Event.MouseMove.Y);" but i would like to fix this problem rather to learn than to produce a working code.

Thank you all.

[Laurent]

Your code produces an undefined behaviour, because you use Event.MouseMove outside the event loop; its members may contain anything.

You should use App.GetInput().GetMouseX/Y() instead.

[BorisDieKlinge]

I replaced the line where I moved the corsur by
 Sprite.SetPosition(App.GetInput().GetMouseX(),App.GetInput().GetMouseY());

But the problem remains.
I don't have a clue why...

Maybe somebody may compile my code to see what i mean?

[Laurent]

But why can I actually SEE this?

Your application runs at X frames per second, whereas the mouse sends its position to the system Y times per second. In your case, X is probably lesser than Y.

[BorisDieKlinge]

...
But....
well. I understand your argumentation. But see:


App.Clear();
Clears the Screen. This means that the stuff actually displayed on screen is the stuff from the last frame.

App.Draw(Sprite);
Drwas the Sprite onto the Buffer.

App.Display();
Displays the content of the Buffer at the screen.

I actually don't get why the framerates X and Y have something to do with this, as the there should be nothing displayed what happens between App.Clear(); and App.Display();
So...

The Problem is gone as I suddenly, by writing this post, understand what happens    

When you call
Sprite.SetPosition(Event.MouseMove.X,Event.MouseMove.Y);
the position of your cursor might be P(100,110).
This means that the Sprite will be drawn at this point P.

App.SetCursorPosition(100,100);
resets the cursor back to P(100,100). But during the time between this App.SetCursorPosition(100,100); and the next Sprite.SetPosition(Event.MouseMove.X,Event.MouseMove.Y); the position of the cursor might chang again to, e.g. P(132,83).

Well, thats it.
Maybe some other noobs like me can make use of my Problem

Thank you for your help
greetings BorisDieKlinge
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