# Difference between revisions of "Layers"

Layers are ConTeXt's mechanism for absolute positioning of elements and other advanced techniques like switching elements on and off.

There's still no manual about them.

# My first Layer

Define a layer that takes the whole page, but starts with an offset

```\definelayer	[mybg]	% name of the layer
[x=-3mm, y=-3mm,	% bleed over the page
width=\paperwidth, height=\paperheight]
```

Now you can put something on that layer:

```\setlayer	[mybg]	% name of the layer
[x=2cm, y=5cm]	% placement (from upper left corner of the layer)
{\framed[frame=on, width=3cm, height=2cm]{LAYER}}
```

Activate the layer as a background:

```\setupbackgrounds	[page]	[background=mybg]
% switch it off again:
\setupbackgrounds	[page]	[background=]
```

You could also typeset the layer once using \placelayer or \flushlayer, but then the location depends from the upper left of the text area! (Bug?)

## Placement

There are several possibilities for defining the placement of layer content:

• x, y (or hoffset, voffset) : offset from upper left corner
• corner : reference point, something like `{left, top}`
• location : alignment of the element relative to the corner, something like `{right, bottom}`
• preset : a named location, see below

There are some "presets" for paper egde placement:

```% These four are defined by ConTeXt!
\definelayerpreset	[lefttop]	[corner={left,top}, location={right,bottom}]
\definelayerpreset	[righttop]	[corner={right,top}, location={left,bottom}]
\definelayerpreset	[leftbottom]	[corner={left,bottom}, location={right,top}]
\definelayerpreset	[rightbottom]	[corner={right,bottom}, location={left,top}]
```

Similarly you can define your own presets.

# Links

 TODO: We need a lot of documentation and samples for this complicated subject. (See: To-Do List)