On 2018-01-03 16:16, Mark Waddingham via use-livecode wrote:
Please post whenever you find or write such a general
"flatten-to-path".
Assuming that 'flatten-to-path' means:
"Produce a compound path which, when filled, produces the same result
as filling and/or stroking a sequence of paths and/or shapes."
Then, in full generality, this is really quite complex - particularly
if you want to preserve curves (which is important if you want your
resulting path to scale arbitrarily).
There are two pieces:
1) A 'thicken' operation which takes a path and stroke properties as
input and produces a path which can be filled to produce the stroke.
(i.e. the 'inside' of the path is the same as the 'inside' of the
stroke of the original path).
2) A 'union' operation which takes two arbitrary paths and produces
a single path which, when filled, produces the same result as filling
the first path, and then filling and compositing the second path on
top of it. (i.e. the 'inside' of the path is the same as the union of
the 'insides' of the two input paths).
For what its worth, I found that Skia (in principal) has boolean path
operation support (i.e. the critical union operation!) -
https://skia.org/dev/present/pathops.
As we also need something along these lines to support the general
'clipPath' element in SVG, I had a go at implementing a simple shape
abstraction.
A shape is basically an expressing where the factors are
paths/ellipses/rectangles/polygons etc. and the operations are:
- transform
- fill (turn the shape into non-intersecting regions relative to a
fill rule)
- dash
- thicken (apply stroke attributes to create the thickened lines which
are filled to form a stroke)
- union / intersect / difference / xor
So you can do things like:
union(fill(thicken(... circle ...), fill(thicken(... square ...))
It seemed to work fine on simple unions/intersections of thickened
squares circles - as long as there was no collinearity / difficult
intersections. However, when I tried some of the simple feature icons -
it did not work so well :(
Basically, the version of the path-ops we have in the version of Skia we
use seem to suffer from some rather unfortunate collinearity / numerical
issues - of course, updating Skia *might* fix the problem, however it
seems that quite a bit has changed since we last updated Skia so that is
not a 'drop-in replacement' type of thing *sigh*.
Warmest Regards,
Mark.
P.S. One thing I do need to try is 'fuzzing' the shapes before applying
the boolean ops - i.e. adding a tiny random delta, small enough that you
won't notice when rendered, but large enough that it turns any difficult
intersections into easier ones.
--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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