Re: Shading and transparency

[Marco Patzer <lists@homerow.info>]

On Thu, 12 Jul 2018 11:21:45 +0200
Hans Hagen <j.hagen@xs4all.nl> 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.

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.

Marco
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