Re: [Plib-users] Invert?

[Steve B. <sjb...@ai...>]

Brad Colbert wrote:

> In version 1.0.20 doing a search on all files I was unable to find
> a reference to sgInvertMat4.  Do I have a wrong version?

Well, it's been a long time since I last thought about 1.0.anything...
perhaps it's time to upgrade to 1.1.  I *thought* that sgInvertMat4
had been around back then - but evidently not.

We are very close to getting a new 'stable' (even numbered) version
out (it'll be 1.2.0) - so 1.1 is pretty good...certainly it's more
stable than 1.0.20.
 
> Is it safe to use this function to get the inverse of the projection matrix?

Yes - although there ARE classes of matrix that are fundamentally,
mathematically, non-invertable.

Any matrix that maps a bunch of points to the same place is NOT
invertable (think about it - if you had an inverse then you could
give that matrix that one magic place and it would have to guess
which of the original points it came from...so those kinds of
inversions are IMPOSSIBLE).

However, perspective isn't like that - so it's invertable.

sgInvertMat4 complains if it is given a non-invertable matrix
as input...so just keep an eye on stderr while debugging.

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
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