[NTG-context] Touch my cow: Overlaying a picture with links to text

[Axel Kielhorn <tex@axelkielhorn.de>]

Hello,

I’m trying to make our documentation more interactive.

So far I managed to turn the labels in the picture into links.

The next step would be to mark certain areas in the picture.
When the reader clicks on these areas, they will follow the link.

This is where I am so far:

% !TEX TS-program = ConTeXt (LMTX)

\setupinteraction[state=start, color=middleblue]
\placebookmarks[section]

\setupexternalfigures[location=default]
\starttext

\startMPinclusions

color mycolor;

def gridscaled =
  pair ur;
  ur = urcorner currentpicture;
  width :=  xpart ur;
  height := ypart ur;
  xstep := ceiling(width / 10);
  ystep := ceiling(height / 10);
enddef;
% Bottom: The annotation is at the bottom of the start point                              
def annotb (expr a,  b, c, d) (text t) =
label.bot ("\framed[background=color,backgroundcolor=transparentwhite,align=normal,corner=00,frame=no]{" & t &"}", (a * xstep,  b * ystep));
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .8mm withcolor white;
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .5mm withcolor mycolor;
enddef ;
% Top: The annotation is on top of the start point                              
def annott (expr a,  b, c, d) (text t) =
label.top ("\framed[background=color,backgroundcolor=transparentwhite,align=normal,corner=00,frame=no]{" & t &"}", (a * xstep,  b * ystep));
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .8mm withcolor white;
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .5mm withcolor mycolor;
enddef ;
% Right: The annotation is on the right of the start point                              
def annotr (expr a,  b, c, d) (text t) =
label.rt (t, (a * xstep,  b * ystep));
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .8mm withcolor white;
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .5mm withcolor mycolor;
enddef ;
% Left: The annotation is on the left of the start point                              
def annotl (expr a,  b, c, d) (text t) =
label.lft (t, (a * xstep,  b * ystep));
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .8mm withcolor white;
	drawarrow (a * xstep, b * ystep) -- ( c * xstep, d * ystep)
		withpen pencircle scaled .5mm withcolor mycolor;
enddef ;
% touchtolink                             
def touchtolink (expr a,  b) (text t) =
label ("\framed[background=color,backgroundcolor=transparentwhite,align=normal,corner=00,frame=no]{" & t &"}", (a * xstep,  b * ystep));
enddef ;
\stopMPinclusions

\startMPpage
% Picture
draw externalfigure "cow.pdf" xsized 16cm;
% Grid
gridscaled;
% Text
annotb (1, 5, .8, 7.3, "\goto{Maul}[Maul]");
touchtolink (.8, 7.3, "\goto{\blackrule[height=2cm, width=4cm, color=transparentwhite]}[Maul]");
annotb (6, 2, 7, 3.2, "\goto{Euter}[Euter]");
annott (9.2, 9.5, 9.6, 3, "Schwanz");
annotb (3, -.5, 3.1, .9, "\goto{Huf}[Huf]");
annotb (3, -.5, 3.9, 1.1, "");

\stopMPpage


\startsection[
    title={Das Maul},
    reference=Maul,
    bookmark={Maul},
    ]
    Lorem ipsum dolor
  \stopsection

\startsection[
    title={Die Hufe},
    reference=Huf,
    bookmark={Huf},
    ]
    Lorem ipsum dolor
\stopsection

\startsection[
    title={Das Euter},
    reference=Euter,
    bookmark={Euter},
    ]
    Lorem ipsum dolor
\stopsection

\stoptext
%%%%

I filled the area with a \blackrule, which is transparent and the link works.
Only problem the frame is filled with the link color, in this case blue.

How do I suppress the color for this link only?
Adding [color=transparentwhite] to the \goto command didn’t help.

Is there a more elegant way to define this area?

Greetings from the snowy pastures of northern Germany
Axel

 
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