Software Quake Frame Interpolation - Implementation Notes
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This is based on the old QER interpolation tutorial; search on archive.org or elsewhere for old content from
http://www.planetquake.com/qer

I don't touch on movement interpolation here; you'll need to do it yourself.  The info in the old tutorial should be
enough to get you going with that.  I advise moving the code for this from R_RotateForEntity to CL_RelinkEntities so
that it's available to both GL and software Quake and so that you don't need special exceptions for the viewmodel.

If you're only interested in frame interpolation you can ignore the QER stuff.  You'll need to add the following to your
entity_t struct (in render.h) if so:

	// frame interpolation
	float frame_start_time;
	int   lastpose;
	int   currpose;

	// even if you've already done the QER stuff you'll need this too!
	int   lastframe;

In addition to the supplied r_alias.c there are two other changes you need.

Firstly, in Mod_LoadAliasModel, add the following line just after bounds-checking pmodel->numverts

	R_CheckAliasVerts (pmodel->numverts);

Secondly in R_NewMap, add the following line just about anywhere you please!

	R_FinalizeAliasVerts ();

