Frank Sullivan wrote:
> i.e., the identity matrix still has me looking down the -z axis, just
like OpenGL, even though in the osg World, I'm looking downwards.
I don't know whether this will clarify or muddy the concept, but I'll
throw it out anyway.
I've been on somewhat of a crusade to rid people of the notion that
OpenGL has a "default" coordinate system. Here's my reasoning behind
that idea...
OpenGL has a ModelView matrix. By default, it's the identity, and in
that case, object coordinates are effectively eye space coordinates, so
therefore the eye is looking along the -Z axis with +Y up. That's all
true, BUT... How many first-person rendering systems use the ModelView
matrix unmodified? The answer is none, they all set the ModelView matrix
to something, and when app software sets that matrix, the app _must_
make a choice about what _it_ wants for a coordinate system. The OpenGL
default is therefore irrelevant.
All too often, this notion of a "default coordinate system" seems to
restrict our thinking and make us believe that there are limitations on
how we can orient the world. I just want to point out that the idea of a
default coordinate system is really a myth.
Paul Martz
Skew Matrix Software LLC
_http://www.skew-matrix.com_ <http://www.skew-matrix.com/>
+1 303 859 9466
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