Re: presentations in ConTeXt

[Vit Zyka <vit.zyka@seznam.cz>]

Mojca Miklavec wrote:
> On 5/23/05, Thomas A. Schmitz <thomas.schmitz@uni-bonn.de> wrote:
> 
> 
>>I am still at a loss how to achieve one thing in ConTeXt that was
>>pretty easy in Keynote or (shudder) Powerpoint: When I wanted to
>>highlight something on a map or a picture, I would just draw a red
>>circle around it. What would be the proper way to do this in ConTeXt?
>>Adding a layer with a red circle drawn in Metapost, then positioning
>>it by trial and error? Or can anyone point to a better solution?
> 
> 
> What kind of picture do you have? If you have .jpg/.png/..., you can
> get (x,y) position of the pixel where the center of circle should be.
> 
> One possibility is to create a new metapost figure and draw the circle
> on it using the measured coordinates:
> 
> (This circles the blue tulip on
> http://contextgarden.net/images/6/65/Kochloewe_c.jpg.)
> 
> \setupcolors[state=start]
> \starttext
> \startuseMPgraphic{CircleBlueTulip}
> 	% center point
> 	pair size, c;
> 	% figure will be 10 cm wide
> 	scale := 10cm/400;
> 	
> 	% center of the blue tulip is on (219,333), image is 400*460
> 	size := (400,460) scaled scale;
> 	c := (222,460-330) scaled scale;
> 	% diameter of the circle should be 50 pixels
> 	d := 50scale;
> 
> 	pickup pencircle scaled 2pt;
> 
> 	externalfigure "Kochloewe_c.jpg" xyscaled size;
> 	draw fullcircle scaled d shifted c withcolor red;
> \stopuseMPgraphic
> 
> \useMPgraphic{CircleBlueTulip}
> 
> \stoptext
> 
> I believe there exists a more straightforward way if you make
> uniqueMPgraphic and specify coordinate fractions of the circle to be
> drawn, but if you say:
> 
> \framed[background=SomeGraphicWithACircle]{\externalfigure[Kochloewe_c][width=10cm]},
> the circle (if any) is drawn behind the figure and cannot be used as
> such. Unless you specify the figure in a new layer and draw both
> layers in the proper order.
> 
> In this case it would be fine to have a \framed[...foreground=...] command :)

Use

\framed
   [background={foreground,BgFront}]
   {\externalfigure[Kochloewe_c][width=10cm]}}

Define your picture as BgFront. 'foreground' is fixed word that 
identifies layer 0 (text). So you can stack bacground as follow:
   background={...,MyLayer-2,MyLayer-1,foreground,MyLayer1,MyLayer2,...}

Vit