Delta Function

Is there a delta function?

I'm not sure what you're referring to. These delta functions? The TimeDelta expression?

http://en.wikipedia.org/wiki/Delta_%28letter%29

The way I understand it is that it's the rate of change of a number.

Δx simply means the change in x, for example, if you wanted to track the change in the mouse X co-ordinate, you'd just subtract the old mouse co-ordinate from the new one.

You might be referring to differentiation, in which case no, that's mathematically fairly advanced and beyond the scope of your typical game.

Where would I get the old coordinate of an object then?

Just store it in a private variable, eg:

Always

Text object: set text to Sprite.X - Sprite('OldX')

Sprite: Set 'OldX' to Object.X

The text object will show the change, frame-by-frame, in the X co-ordinate.

Just store it in a private variable, eg:

Always

> Text object: set text to Sprite.X - Sprite('OldX')

> Sprite: Set 'OldX' to Object.X

The text object will show the change, frame-by-frame, in the X co-ordinate.

Yep, that's how my platform engine tells the difference between jumping and falling. Y < oldY = jumping, and y > oldY = falling. Good for controlling animations.

What would Object.X be though? Do I attach a second invisible sprite to the character or... what?

Sorry, stuffed that one up. Should've been Sprite.X:

Always

Text object: set text to Sprite.X - Sprite('OldX')

Sprite: Set 'OldX' to Sprite.X