Box2D Forums

Hi,

I'm looking for a way to deform the physic shapes.

Say I have a game character standing on a very simple b2body, consisting of one fixture made of edges:


The player wants to dig a hole (like in Lemmings, Lode Runner, etc.). I imagined substracting a "dig" round shape from the ground shape:


The childish formulation of this would be "substract the circle from the rectangle and keep the resulting polygon":


Two questions now...
- Is there anything like this in Box2D?
- (if not) am I making any sense imagining this would be a great solution?

Of course, if you know about a method to accomplish the same result as pictured in my (splendid) drawings... I'll be very glad to hear about it!

edit: I see the following on Wikipedia: http://en.wikipedia.org/wiki/Constructi ... d_geometry seems what I'm trying to achieve has a name Actually willing to get the red box minus blue sphere result. In 2D. And in Box2D

Thanks a lot,
J.

I think the typical way to handle this would be to make the ground from a chain shape. That way, you can just move/add vertices in the chain. These people have done a fine job of it, maybe you could get some inspiration or advice from them:
http://www.youtube.com/user/ChaosReef/videos
http://www.youtube.com/user/TomorrowPlusX/videos
http://www.youtube.com/user/slembcke/videos (this is chipmunk, but the principle is the same)

Hey thanks for the hints. All three examples are very impressive out there... Had seen Slembcke's works earlier today... I want to stick with Box2D though

I'll begin with the source code Slembcke made available... Will share anything useful I'll make out of it!

I've had very good results with Clipper: http://www.angusj.com/delphi/clipper.php

Took me less than a day to create destructible 2d terrain. Here is what I did:
- Represent your terrain with polygons
- Triangulate them for rendering (http://code.google.com/p/poly2tri/)
- Build a box2d edge shape for collision detection using those polygons
- Subtract from your terrain with Clipper library (clip type of 'Difference') -> results in a new list of polygons
- Re-triangulate and rebuild the edge shape with the new polygons

Hope that helps!

- Shlomo