Re: multiple backgrounds

[Hans Hagen <pragma@wxs.nl>]

� wrote:

>On Sun, 15 Jan 2006, Henning Hraban Ramm wrote:
>
>  
>
>>Now I must only find a way to *subtract* a layer, but I guess I can  
>>manage that with some "doifmode"s
>>    
>>
>
>Hello TeX-experts,
>
>I tried to do the layer-subtraction, but it seems that I need more
>experience with expansion in TeX. Here is the error:
>! Undefined control sequence.
>\GetList #1,#2;->\edef \ListHead 
>
>And here my test file:
>
>\def\GetList#1,#2;{\edef\ListHead{#1}\edef\ListTail{#2}}
>\def\Remove#1#2{\doRemove{#1}{#2,\relax}}
>\def\doRemove#1#2{\expandafter\GetList#2;%
>  \doifelse{\ListHead}{#1}{}{\ListHead,}%
>  \doifelse{\ListTail}{\relax}{}{\doRemove{#1}{\ListTail}}%
>}
>
>\def\addBGbefore#1{\expandparameters
>  \setupbackgrounds[page][background={#1,\currentvalue}]}
>\def\addBGafter#1{\expandparameters
>  \setupbackgrounds[page][background={\currentvalue,#1}]}
>\def\removeBG#1{\expandparameters
>  \setupbackgrounds[page][background={\Remove{#1}{\currentvalue}}]}
>
>\setupcolors[state=start]
>\defineoverlay[layer1][{\color[red]{this is layer 1}}]
>\defineoverlay[layer2][{\rotate[rotation=30]{\color[blue]{this is layer 2}}}]
>\defineoverlay[layer3][{\rotate[rotation=60]{\color[green]{this is layer 3}}}]
>
>\starttext
>\addBGafter{layer1}
>\input tufte
>\page
>\addBGafter{layer2}
>\input tufte
>\page
>\addBGbefore{layer3}
>\input tufte
>\page
>\removeBG{layer2}
>\Values
>\input tufte
>\page
>\removeBG{layer1}
>\input tufte
>\stoptext
>
>  
>
i dunno what you want to to, but why not

background={l-1,l-2,l-3,l-4}

and simply set and reset layers, with

\defineoverlay[l-1][] % gone

\defineoverlay[l-1][present]

\defineoverlay[l-1][] % gone again

Hans