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<TITLE>The mtPaint Handbook - Chapter 8 - Layers</TITLE></HEAD><BODY BGCOLOR="white" TEXT="black">
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<H1>8. Layers</H1>
<P>
For some types of painting and image manipulation it is convenient to use
multiple layers of images rather than a single image. For example you may want
to overlay text or drawings over a photograph and then be able to move or edit
each layer independently.
</P>
<A NAME="SEC1"></A>
<H2>8.1 Creating</H2>
<P>
To create a new layer, you can use the Layers window ('L' key or View menu), or
the Layers menu. Same as with new image, new layer can be created either empty
or from a screenshot, or from clipboard. You can then edit, manipulate, load to,
or save this new layer just like any other image.
</P>
<P>
The background layer has some special properties. It sits below all other layers
and cannot be moved around, all transparency in it is ignored when doing
compositing, and the size of the background layer determines the size of the
final composite image. Still, all layers are created equal - you can make any
other layer the background, or turn background into a normal layer, by
rearranging layers (raising or lowering).
</P>
<A NAME="SEC11"></A>
<H3>8.1.1 Drag 'n' Drop</H3>
<P>
If you have several images that you want to open as layers, it is possible to do
this using a file manager and its drag 'n' drop facility. Simply select all of
the image files you want using your favourite file manager (e.g. Rox, Konqueror,
Nautilus), and then drag them over the main mtPaint window and release the mouse
button. mtPaint will then load each of the files as a new layer.
</P>
<A NAME="SEC2"></A>
<H2>8.2 Manipulating</H2>
<P>
You can move any layer around by clicking and dragging it in the the view
window, or by pressing CTRL and using the arrow keys (+SHIFT nudges like
pasting). Or you can use coordinate spins in the layers window. There is also a
button on the layers window which puts the layer back to the centre of the
background image.
</P>
<P>
The layers window allows you to name each layer for convenience and to
temporarily hide it by unchecking the toggle button to the right of the layers
name. It also allows you to duplicate, delete, raise or lower layers, and change
their opacity.
</P>
<P>
When you decide you want to save this composite image you use the Layers menu.
Alternately, you can put the composite image into a new layer. If you want to
save information relating to the layers you will need to use the option
'Layers->Save As' which saves a small text file containing information about
each layer.
</P>
<P>
You can then load these layers back into mtPaint by loading the text file.
Please note that when you save the composite image or the text file you are not
saving each individual layer. As mentioned earlier, each layer is considered to
be its own file and must be saved with the 'File' menu or Ctrl-S as normal. The
benefit of treating the layers separately is as follows:
</P>
<UL>
<LI>Less disk space is required as the layers are not clumped together into a new
file.
<LI>Image layers can be edited with any other image editor.
<LI>If you are using a standard image for several composite images (e.g. a
standard logo or piece of text for watermarking photos), you only need to edit
one image and all of the other composite images will be updated automatically
the next time you save them.
</UL>
<P>
After saving the layers text file you must not move it anywhere else unless you
also move the image files with it as these file references are relative. The
simplest method is to keep all original images and text files in a single
directory.
</P>
<A NAME="SEC21"></A>
<H3>8.2.1 Communal undo space</H3>
<P>
When using layers, the undo memory limit set in the preferences window must be
divided by the number of layers to determine the limit per layer. For example,
with a 32MB limit and 4 layers there is an 8MB limit per layer for the undo.
This is because in mtPaint, undo for each layer works independently; you can
undo and redo actions on one layer even if simultaneously editing another.
</P>
<P>
When using many layers, undo memory gets split into uncomfortably small chunks.
Some layers may use only a small part of their undo space allotment, while
others are getting cramped. To alleviate this problem, mtPaint uses so called
"communal undo space". It is a share of undo memory which is available to all
layers, with the current layer having priority. By default it takes 25% of
total undo space. This way, however many layers you have, the layer you're
working with can use more than 25% of undo memory.
</P>
<P>
Still, "communal undo space" is a compromise solution, and imperfect like all
compromises. If the current layer needs more of "communal space" than remains
unused by other layers, then some other layer's undo frames will have to be
freed to get that space (the oldest undo frames of the most "greedy" layers are
freed first). So, when using communal space, per-layer undo is not absolutely
independent anymore. Usually this is not a problem, but if it is, you can reduce
the communal space to 0 in the preferences window. Alternately, you can increase
it, to allow the current layer use more of undo space.
</P>
<A NAME="SEC3"></A>
<H2>8.3 Examples</H2>
<P>
Here are some examples of composite images created by using the layer
facilities. Click on each image to download the source files:
</P>
<P>
<A HREF="../files/8.3a.zip"><IMG ALIGN="middle" SRC="../img/8.3a.png" ALT=""></A> <A HREF="../files/8.3b.zip"><IMG ALIGN="middle" SRC="../img/8.3b.png" ALT=""></A>
</P>
<A NAME="SEC4"></A>
<H2>8.4 Tricks and Tips</H2>
<A NAME="SEC41"></A>
<H3>8.4.1 Creating a Scrapbook using Layers</H3>
<UL>
<LI>Create a new background image which is large enough to hold all of your images
<LI>Select a bunch of image files (e.g. photos or clip art) using your favourite
file manager, and then drag and drop them onto the main mtPaint window to load
them in as new layers
<LI>Position the images in the view window so they are all visible and sit on the
background image
<LI>Create new layers in order to hold individual items of text
<LI>Save the layers file so you can edit the layers at a later date, and then save
the composite image file so you can distribute it as a standard PNG/JPEG image
</UL>
<A NAME="SEC42"></A>
<H3>8.4.2 Gradient Stencils</H3>
<P>
If you combine the layers feature with gradients and alpha channels, you can
create some useful stencil based images. For example you can do things like
this:
</P>
<P>
<A HREF="../files/8.4.2.zip"><IMG ALIGN="middle" SRC="../img/8.4.2.png" ALT=""></A>
</P>
<P>
If you click on the above image you can download a zip file containing the
various layer images which you can then study to see how they were created and
how they merge together to create the final composite image.
</P>
<P>
Each object has its own layer so it can be moved independently of the other
objects. Also, you can re-use any of the layers in any other project using any
image editor because they are just RGBA PNG files.
</P>
<P>
The text objects use a linear gradient (or flat black for the shadow) as the RGB
image channel. The text stencil is created by using an alpha channel and pasting
some text onto it.
</P>
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