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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="gimp-paths"></a>4.7. Paths</h3>
</div>
</div>
</div>
<a id="id3309534" class="indexterm"></a>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/using/path-examples.png" />
<div class="caption">
<p>
Four examples of GIMP paths: one closed and polygonal; one
open and polygonal; one closed and curved; one with a mixture
of straight and curved segments.
</p>
</div>
</div>
</div>
<p>
A <span class="emphasis"><em>path</em></span> is a one-dimensional curve. Paths are
used for two main purposes:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
A closed path can be converted into a selection.
</p>
</li>
<li>
<p>
An open or closed path can be <span class="emphasis"><em>stroked</em></span>,
that is, painted on the image, in a variety of ways.
</p>
</li>
</ul>
</div>
<p>
Paths can be created and manipulated using the <a href="ch03s06.html#gimp-tool-path" title="6.1. Path Tool">Path tool</a>. Paths, like layers and
channels, are components of an image. When an image is saved in
GIMP's native XCF file format, any paths it has are saved along
with it. The list of paths in an image can be viewed and operated
on using the <a href="ch04s04.html" title="4. Path dialog">Paths
dialog</a>. If you want to move a path from one image to
another, you can do so by copying and pasting using the popup menu
in the Paths dialog, or by dragging an icon from the Paths dialog
into the destination image's window.
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/using/path-with-anchors.png" />
<div class="caption">
<p>
Appearance of a path while it is being manipulated using the
Path tool. Black squares are anchor points, the open circle
is the selected anchor, and the two open squares are its
handles. Note that this path has two components.
</p>
</div>
</div>
</div>
<p>
GIMP paths belong to a mathematical type called "Bezier paths".
What this means in practical terms is that they are defined by
<span class="emphasis"><em>anchors</em></span> and <span class="emphasis"><em>handles</em></span>.
"Anchors" are points the path goes through. "Handles" define the
direction of a path when it enters or leaves an anchor point:
each anchor point has two handles attached to it.
</p>
<p>
Paths can be very complex. If you create them by hand using the
Path tool, unless you are obsessive they probably won't contain
more than a few dozen anchor points (often many fewer); but if you
create them by transforming a selection into a path, or by
transforming text into a path, the result can easily contain
hundreds of anchor points, or even thousands.
</p>
<p>
A path may contain multiple <span class="emphasis"><em>components</em></span>. A
"component" is a part of a path whose anchor points are all
connected to each other by path segments. The ability to have
multiple components in paths allows you to convert them into
selections having multiple disconnected parts.
</p>
<p>
Each component of a path can be either <span class="emphasis"><em>open</em></span>
or <span class="emphasis"><em>closed</em></span>: "closed" means that the last
anchor point is connected to the first anchor point. If you
transform a path into a selection, any open components are
automatically converted into closed components by connecting the
last anchor point to the first anchor point with a straight line.
</p>
<p>
Path segments can be either straight or curved. A path all of
whose segments are straight is called "polygonal". When you
create a path segment, it starts out straight, because the handles
for the anchor points are intially placed directly on top of the
anchor points, yielding handles of zero length, which produce
straight-line segments. You can make a segment curved by dragging
a handle away from one of the anchor points.
</p>
<p>
One nice thing about paths is that they are very light in terms of
resource consumption, especially in comparison with images.
Representing a path in RAM only requires storing the
coordinates of its anchors and handles: 1K of memory is enough to
hold quite a complex path, but not enough to hold even a 20x20
pixel RGB layer. Therefore, it is quite possible to have
literally hundreds of paths in an image without putting any
signficant stress of your system. (How much stress managing them
would put on <span class="emphasis"><em>you</em></span> is, of course, another
question.) Even a path with thousands of segments consumes
minimal resources in comparison to a typical layer or channel.
</p>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3310390"></a>Paths and Selections</h4>
</div>
</div>
</div>
<p>
GIMP lets you transform the selection for an image into a path;
it also lets you transform paths into selections. For
information about the selection and how it works, see the <a href="ch02s04s04.html" title="4.4. The Selection">Selection</a> section.
</p>
<p>
When you transform a selection into a path, the path closely
follows the "marching ants". Now, the selection is a
two-dimensional entity, but a path is a one-dimensional entity,
so there is no way to transform the selection into a path
without losing information. In fact, any information about
partially selected areas (i.e., feathering) will be lost when
the selection is turned into a path. If the path is transformed
back into a selection, the result is an all-or-none selection,
similar to what would be obtained by executing "Sharpen" from
the Select menu.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3310812"></a>Stroking a Path</h4>
</div>
</div>
</div>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/using/path-stroking-examples.png" />
<div class="caption">
<p>
The four paths from the top illustration, each stroked in a
different way.
</p>
</div>
</div>
</div>
<p>
Paths do not alter the appearance of the image pixel data unless
they are <span class="emphasis"><em>stroked</em></span>, using
<span class="guimenu">Edit</span>-><span class="guimenuitem">Stroke Path</span>
from the image menu or the Paths dialog right-click menu, or the
"Stroke Path" button in the Tool Options dialog for the Path
tool.
</p>
<p>
Choosing "Stroke Path" by any of these means brings up a dialog
that allows you to control the way the stroking is done. You
can choose from a wide variety of line styles, or you can stroke
with any of the Paint tools, including unusual ones such as the
Clone tool, Smudge tool, Eraser, etc.
</p>
<p>
You can further increase the range of stroking effects by
stroking a path multiple times, or by using lines or brushes of different
widths. The possibilities for getting interesting effects in
this way are almost unlimited.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3310885"></a>Transforming Paths</h4>
</div>
</div>
</div>
<p>
Each of the Transform tools (Rotate, Scale, Perspective, etc)
can be set to act specifically on paths, using the "Affect:"
option in the tool's Tool Options dialog. This gives you a
powerful set of methods for altering the shapes of paths without
affecting other elements of the image.
</p>
<p>
By default a Transform tool, when it is set to affect paths,
only acts on a single path: the <span class="emphasis"><em>active
path</em></span> for the image, which is shown highlighted in the
Paths dialog. You can make a transformation affect more than
one path, and possibly other things as well, using the
"transform lock" buttons in the Paths dialog. Not only paths,
but also layers and channels, can be transform-locked. If you
transform one element that is transform-locked, all others will
be transformed in the same way. So, for example, if you want to
scale a layer and a path by the same amount, click the
transform-lock buttons so that "chain" symbols appear next to
the layer in the Layers dialog, and the path in the Paths
dialog; then use the Scale tool on either the layer or the path,
and the other will automatically follow.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3310826"></a>Paths and Text</h4>
</div>
</div>
</div>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/using/path-from-text.png" />
<div class="caption">
<p>
Text converted to a path and then transformed using the
Perspective tool.
</p>
</div>
</div>
</div>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/using/path-text-stroked.png" />
<div class="caption">
<p>
The path shown above, stroked with a fuzzy brush and then
gradient-mapped using the Gradient Map filter with the
"Yellow Contrast" gradient.
</p>
</div>
</div>
</div>
<p>
A text item created using the Text tool can be transformed into
a path using the "Create path from text" button in the Tool
Options for the Text tool. This can be useful for several
purposes, including:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Stroking the path, which gives you many possibilities for
fancy text.
</p>
</li>
<li>
<p>
More importantly, transforming the text. Converting text
into a path, then transforming the path, and finally either
stroking the path or converting it to a selection and
filling it, often leads to much higher-quality results than
rendering the text as a layer and transforming the pixel
data.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3310870"></a>Paths and SVG files</h4>
</div>
</div>
</div>
<p>
SVG, standing for "Scalable Vector Graphics", is an increasingly
popular file format for <span class="emphasis"><em>vector graphics</em></span>, in
which graphical elements are represented in a
resolution-independent format, in contrast to <span class="emphasis"><em>raster
graphics</em></span>, in which graphical elements are represented
as arrays of pixels. GIMP is mainly a raster graphics program,
but paths are vector entities.
</p>
<p>
Fortunately, paths are represented in SVG files in almost
exactly the same way they are represented in GIMP. (Actually
fortune has nothing to do with it: GIMP's path handling was
rewritten for GIMP 2.0 with SVG paths in mind.) This
compatibility makes it possible to store GIMP paths as SVG files
without losing any information. You can access this capability
in the Paths dialog.
</p>
<p>
It also means that GIMP can create paths from SVG files saved in
other programs, such as <span class="application">Inkscape</span> or
<span class="application">Sodipodi</span>, two popular open-source
vector graphics applications. This is nice because those
programs have much more powerful path-manipulation tools than
GIMP does. You can import a path from an SVG file using the
Paths dialog.
</p>
<p>
The SVG format handles many other graphical elements than just
paths: among other things, it handles figures such as squares,
rectangles, circles, ellipses, regular polygons, etc. GIMP 2.0
cannot do anything with these entities, but GIMP 2.2 can load
them as paths.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="../images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
Creating paths is not the only thing GIMP can do with SVG
files. It can also open SVG files as GIMP images, in the usual
way.
</p>
</td>
</tr>
</table>
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