How do I keep physics gravity while resizing a sprite?

I've looked all around and don't understand why gravity stops working when a physics object gets resized.

This capx I made has one event. If you disable it the sprites fall like a normal physics object would. Any ideas? Is this a bug or is this just how physics objects work? I'm using r239.

https://dl.dropboxusercontent.com/u/19590484/resizing%20physics%20objects.capx

See Ashley's response here to a similar problem reported as a bug. Every time you change animation frame, or resize an object (as in your case), the physics body inside the physics engine has to be replaced.

[quote:2yka3vxj]The Physics behavior treats a change of frame as destroying the physics body and teleporting a new one in its place (to take in to account changing collision poly, size, origin etc). Therefore animating objects keeps destroying the physics body you're applying force to.

Hey thank you for pointing me in the right direction.

Use a placeholder (invisible sprite) to keep the physics and your sprite as an image only.

Any recalculation of the collision polygons (sine, scaling, animation) will give you a memory related java error, when physics is used, anywayz.

Depending on how many affected objects, the error pops up in 1 minute or 20 minutes later.

Try it, give the objects in your capx a sine (on size) behaviour. Empty event sheet.

Try

?

You can also save the velocity and angular speed to variables before setting the size and setting the velocty from the variables after.

R0J0hound

I tested his capx with your excellent Chipmunk Physics as engine. The objects fall and collide while resizing. Even with a sine behaviour (size) attached. So it works flawless as one would expect.

But now, after your suggestion, i doubt my suggestion. Does Chipmunk has the same (or other) problems with recalculating polygons ? (As in animations by instance)

It's just an alternate idea of one doesn't want to use a third party behavior. Chipmunk does also recreate the shape but the velocity is retained. There isn't a crash if you do it continuously. All the old shapes should be cleaned up by the garbage colllector.