Re: [ft-devel] Signed distance fields: distance from any point to the glyph contours

[Nicolas Rougier]

Yes, I had a look at glyphy code and the output is really nice but the code is 
not so easy to read.

What I had in mind was to generate the distance field on the software side 
using exact distances (instead of approximating them from a rasterized glyph) 
an to store the results in a texture. I know the result will be not so good at 
very high resolution but this is a really fast rendering method with acceptable 
results in a lot of cases. My secret hope was that freetype would have such 
distance computation (somewhere for some reason) even if not publicly available 
through the API...


Nicolas


On Oct 31, 2012, at 17:03 , Behdad Esfahbod wrote:

> On 12-10-31 07:25 AM, Alexei Podtelezhnikov wrote:
>> On Tue, Oct 30, 2012 at 6:56 AM, Nicolas Rougier
>> <address@hidden> wrote:
>> 
>>> My question relates to a more direct way to compute the signed distance and 
>>> to know if anyone has already coded it by any chance ? Said differently, is 
>>> there a quick way to compute the shortest signed distance from any point 
>>> (x,y) to the glyph contours ?
>> 
>> Quick? I do not think so. A glyph outline is a collection of contours
>> is a collection of straight segments and Bézier curves.For the
>> straight segments it is trivial. It is very difficult but surely
>> doable for the conic and cubic curves. No it is not implemented.
> 
> Distance to a cubic Bezier involves solving a fifth degree polynomial.  There
> are acceptable approximations.  As usual, Jim Blinn has the answer.
> 
> My approach in GLyphy (glyphy.org) has been different: I approximate the
> Bezier with a circular arc spline and arrange the resulting splines in a grid
> for fast random access.  The algorithms involved can be made fast, and are
> mathematically very stable.  The arc approximation is part of GLyphy API if
> you are interested.
> 
> Cheers,
> behdad