determining how to bounce the ball

**wysota** · 24th December 2007, 13:49

Originally Posted by aamer4yu

When you get a list of items, u can check to which class it belongs using dynamic cast,,, or u can use a extra variable in the class.

qgraphicsitem_cast() is the way to go.

**Binji** · 26th December 2007, 19:04

Thanks i (think i) understand how to detect objects now.
How about the second half of the question? Any ideas? Maybe if i try translating current position of the ball to the hit item's coordinate system and see if it does? Or is there a better way?

**wysota** · 26th December 2007, 20:53

QGraphicsItem::collidingItems() returns a list of items colliding with a particular item.

**Binji** · 26th December 2007, 23:31

Originally Posted by wysota

QGraphicsItem::collidingItems() returns a list of items colliding with a particular item.

I meant how to determine how to bounce the ball off the hit object. Or am i missing something?

**wysota** · 26th December 2007, 23:37

Hmmm... what do you mean "how"? You mean physics?

BTW. Have you seen this?
http://doc.trolltech.com/qq/qq20-jambi.html

**Binji** · 29th December 2007, 11:08

I have seen that example but except for some code for working with the scene there isnt really anything i need.
And to explain what i need... right now i have a ball object which has x and y velocity. So every time a time trigger triggers i move it by that values. But now i dont know whether the ball hit something by its x axis (where i have to invert the x velocity) or y axis (where i have to invert the y velocity).
One idea i had is to move the ball only by x or y every time i have a time trigger event and then check for collision but im not sure if its such a good idea.
So if you have a better idea it would really mean a lot

Thanks

edit: damn im dumb.. if i get a list of items colliding with the ball i can simply check which coordinates equals those of the ball.

**wysota** · 29th December 2007, 12:24

Originally Posted by Binji

edit: damn im dumb.. if i get a list of items colliding with the ball i can simply check which coordinates equals those of the ball.

They might not be "equal". Collision is determined by shape, not by the centre point, so you can hit "by the corner" as well and "harder" in one direction than in the other. But these are all simple calculations.