Re: multiple backgrounds

["Peter Münster" <pmlists@free.fr>]

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

Cheers, Peter

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