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< [[Layout]] | [[Columns]] | [[Overlays]] | [[Logos]] | [[Collectors]] >
'''Layers''' are ConTeXt's mechanism for absolute positioning of elements and other advanced techniques like switching elements on and off.
There's There’s still no manual about them.
==My first Layer==
Define a layer that takes the whole page, but starts with an offset
<texcode>
\definelayer [mybg] % name of the layer [x=-3mm0mm, y=-3mm0mm, % bleed over the pagefrom upper left corner of paper width=\paperwidth, height=\paperheight]% let the layer cover the full paper
</texcode>
Now you can put something on in that layer:
<texcode>
\setlayer [mybg] % name of the layer [xhoffset=2cm1cm, yvoffset=5cm1cm] % placement (from upper left corner of the layer) {\framed[frame=on, width=3cm, height=2cm]{LAYER}} % the actual contents of the layer
</texcode>
Activate the layer as a background:
<texcode>
\setupbackgrounds [page] [background=mybg]
</texcode>
This command makes the contents of the layer appear only once after the background is activated. If you want to repeat the contents of the layer on each page, use the option <code>repeat=yes</code> in the {{cmd|definelayer}} command. Then the contents of the layer will be shown on every page. You can add to these contents by a new {{cmd|setlayer}}[mybg] command. To clear the accumulated contents use {{cmd|resetlayer}}[mybg]. To make the layer appear on each page, so that it can be populated with different content, set the option <code>state=repeat</code> in {{cmd|setupbackgrounds}}.
You could also typeset Now you can test the layer once using <cmd>placelayerwhole thing:</cmd> or <cmd>flushlayer</cmdcontext source=yes>\setuppapersize[A10][A9, but then landscape]\setuparranging[2UP] % two pages side by side\showframe % show entire pages \definelayer[mybg] % name of the location depends layer [x=0mm, y=0mm, % from upper left corner of paper width=\paperwidth, height=\paperheight, % let the layer cover the full paper ] \setupbackgrounds[page][background=mybg] \setlayer[mybg] % name of the layer [hoffset=0.2cm, voffset=0.2cm] % placement (from upper left corner of the text area! (Bug?layer) {\framed[frame=on, width=2cm, height=1cm]{LAYER}} % the actual contents of the layer \starttext \dorecurse{2}{\page[empty]} % for testing, to get 2 pages, 1st with layer, 2nd without \stoptext </context>
* switch off backgrounds: <code>\setupbackgrounds[page][background=]</code>
* add a background: <code>\setupbackgrounds[page][background={\currentvalue, mylayer}]</code>
==Placement==
There are several possibilities for defining the placement of layer content:
* x, y : offset from upper left corner of paper[=the current block; can sometimes be the text area instead of the page/paper!]
* hoffset, voffset : offset from upper left corner of layer
* corner : reference point, something like <code>{left, top}</code>
* preset : a named location, see below
There are some "presets" for paper egde edge placement:
<texcode>
% These four are defined by ConTeXt!
Similarly you can define your own presets.
=Links==Understanding "location" and "corner"=== The layer is divided into a 2x2 matrix of squares, where 'x' is the center. This gets you a total of 3x3=9 different corners. o---o---o | | | o---x---o | | | o---o---o Now you choose one 'corner' (the reference point) for the placement of the content. The content is placed in relation to this point. The chosen 'corner' c is our new 'center point' (only for placement) now. With 'location' you define where (in relation to 'corner') the content is placed. Again you have nine different corners to choose from. ==== Example: to make this clear ==== Specifications <code>corner={top,right},location={bottom,right}</code> will place content in the area L (outside the original layer). Think about the 'corner' c as a magnetic grid point, where the content snaps to. The 'location' defines, from which direction we approach the point c. * x = layer center point* c = corner 'top,right'* d = location 'bottom right'* L = location (area) o---o---o | | | ----o---c---o | | | L | ----x---o---d | | | --------- ==== Example: placing a logo to the top right corner of the page ==== <context source=yes text="gives:">\definelayer [Logo] [location={left,bottom}, x=\paperwidth,y=0mm, hoffset=-5mm,voffset=5mm, ] \setlayer[Logo] {\framed[width=3cm,height=1cm,background=color,backgroundcolor=lightgray]{Logo...}} \setupbackgrounds[page][background=Logo] \starttext %\showframe  Some text...\stoptext</context> ==State== The available options for the "state" of a layer are: * start: layer appears only on the current page* stop: layer doesn't show up* repeat: layer prints on all pages* next: layer appears on the following page* continue: layer appears on all pages except the first ==Line breaking and fixed size== You may experience cases where the defined size of your layer is ignored and you can’t get linebreaking or multiple lines at all.This is due to <cmd>setlayer</cmd> using <cmd>hbox</cmd> internally. You can work around the problem using <cmd>setlayerframed</cmd>: <context source=yes>\setuppapersize[A6] \definelayer[AddressBg][ x=20mm, y=30mm, width=65mm, height=30mm, state=start] % size is ignored!\setupbackgrounds[paper][ setups=ALayer, background=AddressBg, state=start] \starttext\strut\startsetups ALayer \setlayer[AddressBg] % Change this to \setlayerframed to get it to work [width=65mm, height=30mm, frame=off, hoffset=0mm, voffset=0mm, align=right] % You must set align to get multiple lines! { PRAGMA Advanced Document Engineering\crlf Mr. Hans Hagen (the wizard who wrote it all, \CONTEXT\ and everything else, with the help of his little elves)\crlf Ridderstraat 27\crlf 8061GH Hasselt\crlf THE NETHERLANDS }\stopsetups\stoptext</context>  ==Place labels on pictures== Layers can be used to put labels on pictures, alternative ways can be found in the [[manual:details.pdf| Details]] manual(see also [[Collectors]]). <context source="yes">\setupexternalfigures[location={local,default}]% (necessary for the wiki conTeXt live processor) \definelayer [figure][width=\overlaywidth,height=\overlayheight]\defineoverlay[figure][{\directsetup{figure}\tightlayer[figure]}] \setupcolors[state=start] \starttext \startsetups figure \setlayerframed [figure] [preset=rightbottom, x=.25\layerwidth, y=.25\layerheight] {\green HERE} \setlayerframed [figure] [preset=leftbottom, x=.15\layerwidth, y=.35\layerheight] {\red THERE} \stopsetups \externalfigure[cow][background={foreground,figure},width=4cm,height=3cm] \stoptext</context> ==Use dynamic content== The content of layer is fixed after your set it and will appear in the same way on each page. <texcode>\definelayer [pagenumber] [width=\paperwidth, height=\paperheight, preset=middle, state=repeat] \setlayer[pagenumber]{Page \pagenumber} \setupbackgrounds[page][background=pagenumber] \starttext\dorecurse{4}{\page[empty]} % Every page will say "Page 1"\stoptext</texcode> This is not always what you desire like in the example above, where on each page the current page number should be shown and not the number from the first page. To recalculate the content on each new page you have to enclose the <cmd>setlayer</cmd> settings within <cmd>startsetups</cmd> ... <cmd>stopsetups</cmd> andwrite <code>\setupbackgrounds[page][setups=setupname,background=layername]</code> in your document. <texcode>\definelayer [pagenumber] [width=\paperwidth, height=\paperheight, preset=middle] \startsetups layer \setlayer[pagenumber]{Page \pagenumber} \stopsetups \setupbackgrounds[page][setups=layer,background=pagenumber] \starttext\dorecurse{4}{\page[empty]} % You get "Page 1, Page 2" etc.\stoptext</texcode>  Another solution was given by Wolfgang on the mailing list on February 21, 2012. He writes: ''Here is a slightly different version which is better when you need more dynamic layers.'' <texcode> \definelayer [pagenumber][width=\overlaywidth,height=\overlayheight,preset=middle]\defineoverlay[pagenumber][\texsetup{layer}] \startsetups layer \setlayer[pagenumber]{Page \pagenumber} \tightlayer[pagenumber] \stopsetups \setupbackgrounds[page][setups=layer,background=pagenumber] \starttext\dorecurse{4}{\page[empty]}\stoptext </texcode> == Layers and the delayed font mechanism == Until some years ago the Latin Modern font was always automaticallyloaded, regardless of the users choice of font. Font loading takes aconsiderable amount of time (check the stats at the end of a contextrun to get an idea). This led to the question: “Why start loading a big, complex font like Latin Modern before weknow which font the user actually wants to use and waste severalseconds on it, just to start loading the users choice afterwards?” The answer was: ”We delay loading the font until we know which font the user wantsto use. If the user doesn't tell us, then we fall back to LatinModern.” The body font is set up in the setup area (the part above<code>\starttext</code>). That, in turn, means that when having reached<code>\starttext</code>, the users choice of font is known and can be loaded. Itis more efficient if a font other then Latin Modern is used. One drawback is that typeset text in the setup area has no fontsetup and will fall back to Latin Modern Mono. Usually no text istypeset in the setup area. However, layers are an exception anda font needs to be set up beforehand. == See Also ==
* Some applications in the [[manual:details.pdf|Details]] manual
* [[Sample documents]]: [[BusinessCard]] and [[Letter style]]
* Source: [[source:pagepack-lyr.texmkii|pagepack-lyr.mkii]] or [[source:pack-lyr.mkiv|pack-lyr.mkiv]]* Example of [[Alternating backgrounds and repeating layers]] and [[Draft Watermark]]* [http://www.ntg.nl/pipermail/ntg-context/2013/070935.html Layer vs. overlay]by Wolfgang
{{todo|We need a lot of documentation and samples for this complicated subject.}}
 
 
[[Category:Graphics]] [[Category:Layers]]
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