How to set multiple convex polygons to a shape in Box2d?

Question

I am new to Box2d, and I have just learned that it does not support concave polygons. I have read to get around this problem, I should use 2 (or more) convex polygons and apply them to the same shape.

Unfortunately, I have looked for a hours for an example of how to do this, but cant find one that works. Heres my code:

b2PolygonShape spriteShape;    
int num = 6;
        b2Vec2 verts[] = {
            b2Vec2(-32.5f / PTM_RATIO, 52.0f / PTM_RATIO),
            b2Vec2(-60.0f / PTM_RATIO, 26.5f / PTM_RATIO),
            b2Vec2(-58.5f / PTM_RATIO, 17.5f / PTM_RATIO),
            b2Vec2(-34.5f / PTM_RATIO, 7.5f / PTM_RATIO),
            b2Vec2(-11.0f / PTM_RATIO, 25.0f / PTM_RATIO),
            b2Vec2(-17.5f / PTM_RATIO, 47.5f / PTM_RATIO)
        };
        spriteShape.Set(verts, num);

        int num2 = 6;
        b2Vec2 verts2[] = {
            b2Vec2(-26.5f / PTM_RATIO, 1.0f / PTM_RATIO),
            b2Vec2(-34.0f / PTM_RATIO, -13.5f / PTM_RATIO),
            b2Vec2(-26.5f / PTM_RATIO, -32.0f / PTM_RATIO),
            b2Vec2(0.5f / PTM_RATIO, -42.5f / PTM_RATIO),
            b2Vec2(49.0f / PTM_RATIO, -40.5f / PTM_RATIO),
            b2Vec2(49.5f / PTM_RATIO, -14.0f / PTM_RATIO)
        };
        spriteShape.Set(verts2, num2);

This simply overrides the first polygon with the second, instead of combining them. How can I combine them instead?

You don't "apply them to the same shape", you make two separate fixtures. — iforce2d, Jun 18 '12 at 17:45

score 2 · Accepted Answer · edited May 23 '17 at 10:24

2

As iforce2d said you should create multiple fixtures. Please see my answer to this question: Box2d multiple fixtures and positioning

edited May 23 '17 at 10:24

Community

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answered Jun 18 '12 at 18:18

Andrew

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I was thrown off by some wrong info on another site. Thanks for the help! – jvnbt Jun 20 '12 at 21:10

How to set multiple convex polygons to a shape in Box2d?

1 Answers1