Hi,
It's probably not the best solution as it uses the ‘old’ shading method,
but seems to give the result you were expecting:
\startMPpage
pair A,B;
path p, psubPath, asPathEnvelope;
A = (0cm,0cm);B = (5cm,0cm);
p = A{dir 60} .. B;
fill fullsquare scaled 12cm withcolor 0.5[blue,white];
for i = 0 step 5 until 355:
psubPath := (subpath((0.1 * length p), (1 * length p) ) of p) rotated i;
asPathEnvelope := envelope pensquare scaled 0.5mm of psubPath;
fill asPathEnvelope
withshade define_linear_shade((0,0), (cosd(i) * 6cm, sind(i) * 6cm),
0.5[blue,white], white);
endfor;
\stopMPpage
(This code generates about twice as many lines as in your pdf; this can be
reversed by changing the step from 5 to 10.)
My guess is that in your example the shading direction is not rotated with
the path. It should be possible to rotate it by properly using
`withshadedirection` (see section 8.3.3 in the metafun manual),
although after experimenting a bit I could not find an easy way to make it
work. (This does not say much though - I'm definitely not very experienced
in MetaFun.)
Best wishes,
Florent
Le sam. 21 sept. 2024 à 17:51, Keith McKay <mckaymeis...@gmail.com> a
écrit :
> Hi,
>
> I have been playing about with envelopes to produce shaded paths as
> described in the new LuaMetFun manual, see page 105 therein. Using the code
> below I wanted to produce a shaded path, in this case a curve and then
> rotating it in 5 degree steps from 0 to 355 degrees to produce a kind of
> spiral. Here is the code:
>
> \startMPpage
>
> pair A,B; path p, psubPath, asPathEnvelope; A = (0cm,0cm);B = (5cm,0cm); p
> = A{dir 60} .. B; fill fullsquare scaled 12cm withcolor 0.5[blue,white]; for
> i = 0 step 5 until 355: psubPath := (subpath((0.1 * length p), (1 *
> length p) ) of p)rotated i; asPathEnvelope := envelope pensquare scaled
> 0.5mm of psubPath; fill asPathEnvelope rotated i yscaled 1
> withshademethod "linear" withshadecolors (0.5[blue,white],white) ; endfor;
> \stopMPpage
>
> I had expected to get a series of curves where the outer point of the
> curve was white, shading down to 0.5[blue,white] at the inner point of
> the curve.
>
> I was expecting the shading to remain that way, however, as the curve is
> rotated round, the shading effect slowly changes until it is reversed, and
> as it
>
> continues to be rotated it returns to it original shading. Although I
> quite like that effect, it's a nice feature, I would like to be able to
> produce the shading
>
> the way I wanted. A while back Hans explained to me why this happened and
> how I could remedy it, but unfortunately my aged memory has failed me and I
>
> cant remember how to do it. So I thought the youthful brains of the
> ConTeXt group may be able to help out, and it might be of interest in any
> case. I
>
> attach a pdf of the spiral effect.
>
> Best Wishes
>
> Keith McKay
>
>
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