On 2017-01-23 14:09, Rik Kabel wrote:
> On 2017-01-23 00:06, Alan Braslau wrote:
> > On Sun, 22 Jan 2017 22:39:53 -0500 Rik Kabel > <context@rik.users.panix.com> wrote: > >> So, how can I make the 
> inner glyph (‘?’ in the example below) >> transparent, so that the 
> background shows through along with >> anything else that lives on a 
> lower layer? I’ve seen a method for >> constructed shapes, but nothing 
> that I can apply to text glyphs. >> Undraw doesn’t do it. > > Undraw 
> is simply draw using the background color. > > Transparency is a 
> MetaFun extension to MetaPost (so part of > ConTeXt). > > draw q 
> withtransparency (1,0.5) ; % (method,transparency) > > Alan
>
> Hmmm. That does not work for me (with any of many method and 
> transparency values).  The  ‘?’ is solid black. I do see a message in 
> the log that looks related:
>
>     mkiv lua stats  > page group warning: transparencies are used but
>     no pagecolormodel is set
>
> but adding \setcolors[state=start,cmyk=yes] does not change that; both 
> the warning and the solid black glyph remain. Could this be an issue 
> of the PDF viewer? Is it a font issue?
Okay, I got a clean compile using \definecolor and referencing that in 
the MP page.

    \setupbackgrounds
       [page]
       [background=color,backgroundcolor=yellow]
    \definecolor[Transp][r=1,t=0,a=12]
    \definefont
       [DVSrB]
       [file:DejaVuSerif-Bold.ttf]
    \startuseMPgraphic{HeartTest 1}
       picture h,q ;
       h := "♥" infont "\truefontname{DejaVuSerif-Bold.ttf}" scaled 20 ;
       q := textext("{\DVSrB ?}") scaled 10 ;
       q := q shifted - (xpart center q, 12pt) ;
       draw h withcolor blue ;
       draw q withtransparency(12,0) ;
       draw q shifted (72pt,0) withtransparency(12,0) ;
    \stopuseMPgraphic
    \startuseMPgraphic{HeartTest 2}
       picture h,q ;
       h := "♥" infont "\truefontname{DejaVuSerif-Bold.ttf}" scaled 20 ;
       q := textext("\color[Transp]{\DVSrB ?}") scaled 10 ;
       q := q shifted - (xpart center q, 12pt) ;
       draw h withcolor blue ;
       draw q ;
       draw q shifted (72pt,0) ;
    \stopuseMPgraphic
    \starttext
      \useMPgraphic{HeartTest 1}
      \useMPgraphic{HeartTest 2}
    \stoptext

Unfortunately, the result is not what I want. The result is that the “?” 
disappears, allowing the color directly behind it to show through. The 
example above shows that it works with \definecolor but not 
withwithtransparency. I have no idea why, and certainly realize it could 
be my error.

What I want is that the background of the page (yellow in this case) 
should show through. That is what is done with fill / reverse / cycle, 
as in:

    \setupbackgrounds
       [page]
       [background=color,backgroundcolor=yellow]
    \startuseMPgraphic{CircleTest}
       path p,q ;
       p := fullcircle scaled 2cm ;
       q := fullcircle scaled 1cm ;
       fill p -- reverse q -- cycle withcolor blue;
    \stopuseMPgraphic
    \starttext
      \useMPgraphic{CircleTest}
    \stoptext

where the background color (yellow) comes through the inner circle (path q).

Can this be done with text characters? I suspect that the answer is that 
the glyphs have to be converted to paths and that it will only work when 
there are no islands (as in ‘P’).

-- 
Rik