Re: [NTG-context] Shading and transparency

12 Jul 2018


      On 7/12/2018 10:08 PM, Marco Patzer wrote:
...
On Thu, 12 Jul 2018 11:21:45 +0200
Hans Hagen  wrote:
...
...
For the old implementation (pre 2016-ish) I had a working solution
because shading to transparent colours just worked (at least in my
case of a simple transparent shade, nothing fancy), but not so any
longer. With the new implementation I couldn't get it working. But
we discussed that at some point in the past. I believe the gist of
it was “shade-to-transparent is gone”.
i'm not ssure what shade to transparency means
I mean a shade from a colour (e.g. black) to transparent. For
instance this used to work pre 2016:
\setupbackgrounds [page] [background=color, backgroundcolor=lightgray]
\definecolor [trans] [a=multiply, t=1, s=1]
\starttext
\startMPcode
   path p; p:=fullsquare xyscaled (5cm, 5cm);
   fill p
     withshading("linear", ulcorner p, llcorner p)
     withfromshadecolor \MPcolor{white}
     withtoshadecolor   \MPcolor{trans};
\stopMPcode
\stoptext
The shade goes from white to transparent (here lightgray, that's the
page colour). I assume you have an older context laying around to
run the example above.
...
... shades can be transparent currently
Yes, but the *whole* shade is made transparent. Currently I don't
know a way to shade from e.g. black to transparent (no colour). The
colour involved in the shading can't have transparency, or if they
do one has to use \MPcoloronly to get rid of the transparency part.
hm, I'm puzzled as a shade doesn't go between colors + transparent but 
from one color to another (in the same color space) and transparency is 
just a different mechanism

maybe it was some side effect of chosen values / vectors that gave the 
combined impression (which is why i want to see the pdf made by context 
that you use as reference)

anyway, it helps to be in the same color space

\setupbackgrounds [page] [background=color, backgroundcolor=lightgray]

\starttext

\startuseMPgraphic{test}
     graycolor white; white := 1 ;
     fill OverlayBox
         withshademethod "linear"
         withshadedirection shadedup
         withshadefactor 1.5
         withshadecolors (.85white,white)
       % withtransparency (multiplytransparent,.7)
         withtransparency (normaltransparent,.7)
\stopuseMPgraphic

\defineoverlay[test][\useMPgraphic{test}]

\framed
   [align=middle,background={foreground,test}]
   {\samplefile{sapolsky}}

\stoptext
...
So the above old syntax roughly translated to the current
implementation:
\setupbackgrounds [page] [background=color, backgroundcolor=lightgray]
\definecolor [trans] [a=multiply, t=1, s=1]
\starttext
\startMPcode
   path p; p:=fullsquare xyscaled (5cm, 5cm);
     fill p
       withshademethod "linear"
       withshadevector (3, 0)
       %% since "trans" contains transparency, one has to use
\MPcoloronly withshadecolors (white, \MPcoloronly{trans})
       withtransparency (.5, .5)
       %% withtransparency \MPtransparency{trans}
       ;
   \stopMPcode
\stoptext
...
.. so how did that old file (uncompressed pdf) look like then
Just run the first example with an old context version. The file
gradient-t from my last mail was created using inkscape as I don't
want a single project to depend on two different context versions.
you're kidding ... i have no old context on my machine
Hans

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