Geometry Boost List: [ggl] Efficient rotation about a point

Subject: [ggl] Efficient rotation about a point
From: Lee (lee)
Date: 2009-11-29 14:27:16

Can a single matrix properly represent "-translate/rotate/+translate"?
I think the translation component of the matrix would be negated 
resulting in rotation about the origin, losing the "rotation about a 
point" behaviour. No?

Stephen Leary wrote:
> This is usually acomplished by producing a matrix that represents 
> -translate/rotate/+translate then applying that matrix transform once. 
> I havent checked to see if GGL supports matrix transforms but that is 
> how i would approach this use case in "real life". The matrix gets 
> built once and reused as many times as needed.
>
> Stephen
>
> On Sun, Nov 29, 2009 at 6:43 PM, Lee <lee_at_[hidden] 
> <mailto:lee_at_[hidden]>> wrote:
>
>     Hi,
>
>     What is the best way (in terms of efficacy) to rotate a ring about
>     a point in GGL?
>     Looking at GGL it seems right now to require three separate passes
>     over the point
>     data: -translate/rotate/+translate. Can't this be done in some
>     kind of single pass
>     'rotate_about_transformer'?
>