Hello Wolfgang,
thank you for your very detailed answer.
I'll - try to understand how it works, try your examples what they'll produce...
Best regards,
Lukas
On Sat, 12 Jan 2013 08:44:21 +0100, Wolfgang Schuster
<wolfgang.schus...@gmail.com> wrote:
Am 11.01.2013 um 16:32 schrieb Procházka Lukáš Ing. - Pontex s. r. o.
<l...@pontex.cz>:
Hello,
I need to add a text to the FOREGROUND of the page.
- Layers can refer to a page (or its size) and elements in a layer are drawn
BELLOW the (normal) page content.
- Overlays are drawn ABOVE the (normal) page content and their size is given by
an element (often \framed) which uses the overlay.
So - I'd need a layer which would overlay the normal page content (like "foreground" or
"topmost" layer) or an overlay which would refer to (= its size and position would depend
on) the (current) page (instead of e.g. \framed);
it should be a somewhat combination of layers & overlays.
How to achieve this in ConTeXt?
Overlays and Layers are to different mechanism which are powerful when you
combine both but first you have to know what each of them does.
1. Overlays
ConTeXt has a overlay environment which cane used in the text to stack the
arguments on the same spot. When take a close look at the example you can see
each new element is placed on top of the previous element, when you remove the
\strut in the argument you would also notice that each argument is placed
horizontal and vertical centered.
\setupbodyfont[40pt]
\starttext
\startoverlay
{\strut\red m}
{\strut\green a}
{\strut\blue l}
\stopoverlay
\stoptext
After you do know now what overlays are I come to the real overlay mechanism.
Overlays are created with the \defineoverlay command which takes a name for the
overlay and its content. The overlays are then applied to a \framed command or
the background to the page the textblock, header etc.
In the next example I created two new overlays with the names “behind” and
“before” (the name itself doesn’t matter) which I activated in the frame with
tha background key.
\starttext
\defineoverlay[behind][{\blackrule[height=2cm,width=8cm,color=yellow]}]
\defineoverlay[before][{\blackrule[height=8cm,width=2cm,color=orange]}]
\framed
[width=10cm,
height=10cm,
background={color,behind,foreground,before},
backgroundcolor=red]
{\blackrule[width=6cm,height=6cm,color=blue]}
\stoptext
When you look at the arguments of the background key you can used two more
names besides my own “behind” and “before” overlays. The first name in the list
“color” is needed when you can to use the argument of the backgroundcolor key
which puts a color two the whole area of the frame. The second name
“foreground” is more interesting because with this you can place overlays
*before* the content of the frame because “foreground” is the frame text itself.
The differences between the overlay environment at the begin and the overlay
mechanism for framed aren’t so big, only the methods to set them because in the
first case you set the content for each level which the argument in braces
({…}{…}) and in the second case you define them first with \defineoverlay and
set the order in the background key.
2. Layers
When you have used layers the content of each layer was always centered in the
frame but with layers you can put the content from each command at a certain
horizontal and vertical position.
In the following example I created a new layer and set three texts for it which
are afterwards placed in the page which the \flushlayer command.
\starttext
\definelayer[test]
\setlayer[test][x=3cm,y=6cm]{ONE}
\setlayer[test][x=8cm,y=2cm]{TWO}
\setlayer[test][x=2cm,y=9cm]{THREE}
\flushlayer[test]
\stoptext
When you put new some text after \flushlayer would be surprised because it
would end put on the following page but you shouldn’t wonder about this because
layers have nothing to do with the page background or foreground.
What makes the layer and overlay mechanism is interesting is when you combine
them and put the \flushlayer command in a overlay which does now place the
texts before or after the content of a frame. With my next example we’re
finally in the process to combine them.
\setupbodyfont[30pt]
\starttext
\definelayer[behindtext]
\definelayer[beforetext]
\setupbackgrounds[text][background={behindtext,foreground,beforetext}]
\setlayer[behindtext][x=-2cm,y=.75ex]{\red Behind}
\setlayer[beforetext][x=+2cm,y=.75ex]{\yellow Before}
The Text!
\setlayer[behindtext][x=5cm,y=4cm]{\red More background text!}
\setlayer[beforetext][x=3cm,y=8cm]{\yellow More foreground text!}
\stoptext
When you look at the example you can see that haven't created a overlay for
layer even though I said you need it to put the layer after the text. This
isn’t necessary because when you create a new layer context does also create a
overlay with the same name in which the layer is placed. The other question is
how you can place overlays on the text/page when I told before overalls can
only be placed on frame, this is possible because all page elements (textblock,
header, footer and even the page and paper itself) are frames. Even though
these elements are frames they don’t provide all the options from \framed
because they are a special version with less functionality.
Wolfgang
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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the
Wiki!
maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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