Re: Left-handed vs. right-handed

In the best of all possible worlds you would flip a coin and set a
universal convention for your whole project.  Just check the appropriate
box in your authoring application, create your graphics device with a
suitable flag and---oh, wait...

 

Since it's clearly "correct" to be agnostic, I prefer to work with the
chirality that the graphics driver expects.  You may have to apply a
transform with negative determinant to your data somewhere---but I would
rather do that once and for all time in a pre-process.  If you try to
cope in your code you will inevitably end up stuck between artists
(or---worse---mathematicians) who fervently believe the world is
right-handed and a driver which stubbornly assumes it's left-handed.  I
can guarantee that keeping track of where all the minus signs have to go
will hurt your head (been there!).

 

The view matrix is only one of your worries---there are several other
operations which are inherently 3D and come with a sign convention built
in.  The cross-product springs immediately to mind, but the really
filthy one is sampling a cube map---there are six faces, each with an
orientation, so if you have two different coordinate systems floating
around the sheer combinatorial possibilities for screwing this up are
pretty daunting...

 

Graham

 

 

 

From: Eric Haines [mailto:[email protected]] 
Sent: 06 May 2009 05:10
To: Game Development Algorithms
Subject: [Algorithms] Left-handed vs. right-handed

 

I've written up my way of thinking about left-handed and right-handed
world and viewing systems. It's a bit long-winded, but here it is:
http://www.realtimerendering.com/blog/left-handed-vs-right-handed-viewin
g/

 

This topic is in one sense basic stuff, but it leads to so much
confusion. Neither DirectX nor OpenGL does a good job of dealing with
this confusion, IMO. In our book we kind of sidestep the whole issue
(choose RH, stay RH). I'd love to get any feedback and corrections from
people on this list (either here on the list, via private email, or on
the blog), as I expect there are ways of thinking about it I hadn't even
considered or have misinterpreted.

 

Eric

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