Manual control over when to redraw the screen

问题:

I'm trying to make a turn-based roguelike engine thing for XNA. I'm basically porting the game over from a previous work I did using an SDL-based roguelike library called libtcod. How can I modify the basic XNA template thing to make the game not redraw the screen every frame, but, instead, when I want?

回答1:

The correct method for doing this is to call GraphicsDevice.Present() whenever you want to draw the back buffer onto the screen.

Now the difficulty here is that the Game class automatically calls Present for you (specifically in Game.EndDraw), which is something you don't want it to do. Fortunately Game provides a number of ways to prevent Present from being called:

The best way would be to override BeginDraw and have it return false, to prevent a frame from being drawn (including preventing Draw and EndDraw from being called), like so:

protected override bool BeginDraw()
{
    if(readyToDraw)
        return base.BeginDraw();
    else
        return false;
}

The other alternatives are to call Game.SuppressDraw, or to override EndDraw such that it does not call base.EndDraw() until you are ready to have a frame displayed on screen.

Personally I would simply draw every frame.

回答2:

You don't need to inherit from Game class, it is entirely optional. You can write your own class which redraws the screen only when you want. There's some useful code in the class though, so you can use Reflector to copy code from there and then change its logic.