repreated model transformation causing mutation

This is because of the rounding errors of the floating point operations.
You shouldnt keep transformed stuff, because the data will almost always be corrupted.

You should save the original object, and make a rotation matrix every frame, depending on the rotation, use that, and trash the transformed coords.

Yes, you should never alter the original vertices. Leaving your map asside for a moment, think about doing so with your models. Ignoring the Increadible Shrinking Model problem for a moment, you wouldn't want to keep an entire copy of the vertex information for each and every instance of that model in the game would you?

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Original post by xavstone I am using a transformation matrix to repeatedly transform a game map. after a while the the map becomes flat then reduces to a dot. Very inconvenient. Is this becuase my matrix is broken? Is this a natural 'creep' in the maths? Should i cast a new map object from the original to do the transformations on? Has anyone else experienced this?

It's what floating point does for you, repeated transform makes precision worse and worse as already said above.

Rather than what you do, you keep original instances of all your data in memory : meshes (read only), angles (or quaternions), scaling, translation vector.

If you do anything incremental (like an incremental rotation of an object), then you keep as many parameters separated as possible, for example you compute rotation as a separate matrix that you renormalize, reorthogonalize every now and then so that it doesn't shrink, expand and skew. If you do it often enough, things won't pop up as the "correction" will be minor each time.

LeGreg

Thank you, thank you, all, for help with my incredible shrinking models!

Does anyone know if there a common consensus on the best way to copy objects? My models are using inner classes for triangle and vectors coordinates. I can 'deepclone' or 'clone' the models (using java at the moment) but this seems to be putting alot of strain on resources. How would this be done in c++? Create a new object and copy across its vital statistics in loops for transform, then kill the new object after render?