Add flip_y_up_to_z_up method to Matrix4

[FredrikNoren]

This is for converting between models which often come in a y-up coordinate system (maya) and game which often use a z-up system.

Math from http://stackoverflow.com/questions/22571364/threejs-matrix-from-z-up-coordinate-system-to-y-up-coordinate-system

[brendanzab]

Aha, interesting! Will have to think about what the best API/naming should be

[FredrikNoren]

Yeah I was going back and fort a bit. Maybe something like just flip_yz is
easier
On Wed, Sep 14, 2016 at 8:28 PM Brendan Zabarauskas <
notifications@github.com> wrote:

Aha, interesting! Will have to think about what the best API/naming should
be

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[brendanzab]

How likely is it that there are other coordinate systems? And will we need this for the other transformation types? cc. @mhintz

[FredrikNoren]

I think y vs z up is the most common issue.
https://www.reallusion.com/iclone/help/3dxchange5/pro/05_Export/Y_Up_or_Z_Up.htm
for instance. Generally it seems like many 3D tools (but not all) use y up
whereas game engines are split between them (unity uses y and unreal z)
On Thu, Sep 15, 2016 at 5:01 AM Brendan Zabarauskas <
notifications@github.com> wrote:

How likely is it that there are other coordinate systems? And will we need
this for the other transformation types? cc. @mhintz
https://github.com/mhintz

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