cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   xissburg
   Member

   Is it possible to mirror an object by specifying its rotation in a special way? Can I do so using quaternions somehow?

   Thanks.

   Posted 11 months ago #
2. 

   Johnnie Blevins
   Member

   I don't think a 3d rotation can give you a truly mirrored object. For that I believe you would need a 4 dimensional rotation.

   Or you can just scale the object by -1 on the axis normal to your desired reflection. I believe this will also turn the object inside out, in which case you'd need to cull front faces instead of back faces.

   There may well also be a solution using quaternions. I know approximately nothing about those.

   Posted 11 months ago #
3. 

   xissburg
   Member

   Scaling by -1 is a good idea, smart you.. I got this working by checking whether the determinant of the rotational part of the affine transform matrix is negative, then I negate the x value of the scale, and this reflects the mesh along the x axis and also causes the inside of the triangles to be rendered instead. Then, I just set the CC3Node's property shouldCullBackFaces to NO and shouldCullFrontFaces to YES (introduced in cocos3d 0.5.4). It works great now.

   Thanks.

   Posted 11 months ago #

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