Map - Box2D collisions with a large shape

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Map - Box2D collisions with a large shape

(4 posts) (3 voices)

Started 2 years ago by winduptoy
Latest reply from toadkick

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winduptoy
Member
I've got a big map (one big PNG image) and I want to define edges and create a box2d body based on where I want the player to collide. I've used VertexHelper to draw the shapes, but when I use this:
```
b2Vec2 verts[] = {

//I removed a bunch of vertices for brevity.
			b2Vec2(-783.5f / PTM_RATIO, -122.0f / PTM_RATIO),
			b2Vec2(-784.0f / PTM_RATIO, -97.5f / PTM_RATIO),
			b2Vec2(-777.0f / PTM_RATIO, -95.0f / PTM_RATIO),
			b2Vec2(798.0f / PTM_RATIO, -120.0f / PTM_RATIO)
		};

		groundBox.Set(verts, 17);
		groundBody->CreateFixture(&groundBox, 0);
```
but box2d crashes when there's more than 8 vertices.

I don't want to use a tilemap, but what's the best way to make a "collision map" or box2d shape for this?

Thanks!
Posted 2 years ago #
bradparks
Member
hey... i haven't played with it at all, but in Box2d, there's a b2Settings.h file, in which the max # of vertices (8) is defined... So you could increase this constant, but how it affects Box2d, I can't say.... If you look in the docs, you'll probably find it....

http://code.google.com/p/cocos2d-iphone/source/browse/trunk/external/Box2d/Box2D/Common/b2Settings.h?spec=svn1693&r=1693
```
/// The maximum number of vertices on a convex polygon.
#define b2_maxPolygonVertices	8
```
Posted 2 years ago #
winduptoy
Member

yes I saw that, but is there a good way to define a large solid with many vertices? Is there a way to generate a box2d shape from a bitmap image?

Thanks!

Posted 2 years ago #
toadkick
Member

I think what you are looking for is something like LevelSVG (http://www.sapusmedia.com/levelsvg/). Among other things, it lets you trace the edges of your terrain in a SVG tool called Inkscape and imports them into your game as box2D shapes (polygons with 2 verts, or "edge shapes").

LevelSVG may seem expensive at first glance, but to implement a similar tool yourself would likely take at least a couple to a few weeks, and $250 is certainly cheaper than a few weeks worth of work IMHO.

That said, you might be able to find similar freely available tools, I know of a few other people on this forum who are working on some.

Posted 2 years ago #

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