Re: [Lib2geom-devel] Path translations

[Nathan H. <nj...@nj...>]

I thought we had specialised Matrix types translate, scale etc which
you could just specialise the templates on.  (indeed I think if you
use templates here it should 'just work')

njh

On Tue, Nov 12, 2013 at 01:18:16AM +0100, Johan Engelen wrote:
> Hi all,
>    Currently, when translating a path (adding a point), 2geom treats it 
> as any other affine transform. This is quite a performance hit.
> 
> (refresher:
> Path is a collection of Curves. A Curve is a virtual base for many curve 
> types. Because many curve types are not closed under affine transforms 
> (the result after an affine transform can not always be represented as 
> its original Curve type, e.g. HLineSegment after rotation), when 
> transforming a Curve, a new Curve is created that holds the transform. 
> When transforming a path, each Curve is transformed, and thus a bunch of 
> new Curves are created.
> )
> 
> As far as I can see now, all (current) Curve types *are* closed under 
> translations. I think we should enforce this for Curve. I.e., each Curve 
> must implement
>         virtual Curve &operator+=(Point const &);
> I tested the performance increase for special-casing Translate 
> transforms, by adding
>        Path &operator*=(Translate const &m) {
>          *this += m.vector();
>          return *this;
>        };
>        Path &operator+=(Point const &m);
> next to the current
>        Path &operator*=(Affine const &m);
> Of course, more changes were needed, and so far I have only implemented 
> addition for BezierCurveN, just to see the performance increase.
> 
> After the change, the path-operations test runs more than twice as fast.
> 
> Do you have any concerns about enforcing an operator+= implementation 
> for Curves ?
> Interestingly, *all* member functions of Curve are const.
> operator+= would be the first state-changing member function. :)
> 
> Cheers,
>    Johan
> 
> 
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