[cairo] [RFC] cairo_stroke_to_path implementation

Jeff Muizelaar jeff at infidigm.net
Mon Feb 1 18:33:02 PST 2010

On 01/02/10 7:33 AM, Andrea Canciani wrote:
> On Fri, Jan 29, 2010 at 7:16 AM, Jeff Muizelaar<jeff at infidigm.net>  wrote:
>> Here's my current stroke-to-path work. Algorithmically it's basically where
>> I want it to be, however it's still a bit messy, especially
>> cairo-stroke-to-path.c. I welcome any comments about what needs to be done,
>> stylistically and otherwise, before we can add commit this.
> I put it on a branch on git
> (http://cgit.freedesktop.org/~ranma42/cairo/?h=wip/stroke-to-path) to
> make it easier to read it.
> I think it would be quite interesting to check the stroke-to-path
> behaviour by using it to "emulate" stroking on the test suite as it
> would be used on many degenerate cases and a few complex ones. If
> nobody has tried this yet, I'll do it asap and post the results.
I have this set up. However I only ever ran the stroke, spline, dash 
test cases.
> I started reading the code (mainly comments) and I noticed that you
> chose to flatten before doing stroke-to-path for dashed styles as no
> easy way to split the bezier curve at a given length came to you. On
> Graphics Gems V you can find a chpter about "The Length of Bezier
> Curves". It allows to get upper and lower bounds for a bezier curve,
> thus could be combined with bisection to find the value of the
> parameter t at which the curve should be split (when t is known,
> splitting the curve is just a straightforward application of de
> casteljau).
Yeah, I considered this approach but was worried about performance. I'm 
still interested in future exploration in this area.
For what it's worth, Skia has dasher that splits beziers at a given 
length so it might be worth investigating the technique used
there too.
> Moreover you missed quite a lot of opportunities to use some of the
> functions you defined (in particular you often explicitly compute the
> length of a vector_t and then normalize).
> As I'll go on to reading the code I'll try to remove some of this code
> duplication.
Patches welcome :)


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