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Rena
PostPosted: Wed Dec 14, 2011 1:51 am 
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Joined: Sat Feb 05, 2011 8:51 pm
Posts: 30
Very strange issue with b2ChainShape. When creating a chain with just two vertices, it works fine:
Code:
--X, Y, R, G, B, A
   {10,   5,      1,   1,   1,   1},
   {110,   5,      1,   0,   0,   1}


But I wanted to break that line into several small segments of different colours:
Code:
--X, Y, R, G, B, A
   {10,   5,      1,   1,   1,   1},
   {20,   5,      1,   0,   0,   1},
   {30,   5,      1,   1,   1,   1},
   {40,   5,      1,   0,   0,   1},
   {50,   5,      1,   1,   1,   1},
   {60,   5,      1,   0,   0,   1},
   {70,   5,      1,   1,   1,   1},
   {80,   5,      1,   0,   0,   1},
   {90,   5,      1,   1,   1,   1},
   {100,   5,      1,   0,   0,   1},
   {110,   5,      1,   1,   1,   1}

With this setup, a box falls onto the line and immediately rotates to some strange angle and gets stuck inside it.
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Erin Catto
PostPosted: Mon Dec 19, 2011 12:30 am 
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Joined: Thu Sep 06, 2007 12:34 am
Posts: 2931
I'm not seeing this problem. Please use b2World::Dump and file an issue here:

http://code.google.com/p/box2d/issues/list
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Rena
PostPosted: Tue Mar 06, 2012 10:57 pm 
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Joined: Sat Feb 05, 2011 8:51 pm
Posts: 30
Sorry for the delay. Here's a dump of the level. I haven't been able to actually compile the testbed program, so maybe there's an obvious issue that's just not showing up in my engine?

The rectangle at the right is the player character, and falls onto the long straight line below, where it then gets stuck inside.


Attachments:
leveldump.c [8.87 KiB]
Downloaded 67 times
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irresistible force
PostPosted: Wed Mar 07, 2012 2:21 am 
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Joined: Tue Jun 24, 2008 8:25 pm
Posts: 1517
Location: Tokyo
The problem seems to be caused by the first and last vertices being the same, making the final segment co-incident with the first ten segments. I think this would qualify as a self-intersecting chain which are not supported.
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Rena
PostPosted: Wed Mar 07, 2012 2:27 am 
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Joined: Sat Feb 05, 2011 8:51 pm
Posts: 30
Aha, I knew it'd be something dumb like that. I forgot to specify an open polygon in my level definition. :oops: Thanks!
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