Re: [Plib-users] matrix problem with sg

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

FragFreak wrote:

> i looked at the sgMakeLookAtMat4() code and it seams  that the y-z
> coordinates are swapped compared
> to gluLookAt(). can i use the other sg-functions like the gl-functions? or
> does sg use another coordinate system?

SG uses a Z-is-up coordinate system...rotated 90 degrees in pitch compared to
the OpenGL conventions.

That's because I come from a flight simulation background where Z was always
UP before OpenGL even existed because (Latitude,Longitude,Altitude) was
simplistically mapped into (X,Y,Z) in early simulators.

The SG model loaders all correct for that though - so existing 3D models still
work no matter whether the modeller they were created on used Z-is-UP or
Y-is-UP.

You application code has to work with Z-is-UP - but SG makes everything
entirely self-consistant by pre-multiplying the camera coordinates
by a 90 degree pitch rotation matrix before rendering.

In hindsight, this is perhaps unfortunate - but when I wrote SG, it didn't
look like anyone else would ever use it - and my first 'customers' were
the FlightGear team who are writing...A flight simulator!

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