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<a name="Introduction-to-Graphics-Structures"></a>
<div class="header">
<p>
Next: <a href="Graphics-Objects.html#Graphics-Objects" accesskey="n" rel="next">Graphics Objects</a>, Up: <a href="Graphics-Data-Structures.html#Graphics-Data-Structures" accesskey="u" rel="up">Graphics Data Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Introduction-to-Graphics-Structures-1"></a>
<h4 class="subsection">15.3.1 Introduction to Graphics Structures</h4>
<a name="index-introduction-to-graphics-structures"></a>
<a name="XREFgraphics-structures"></a>
<p>The graphics functions use pointers, which are of class graphics_handle, in
order to address the data structures which control graphical displays. A
graphics handle may point any one of a number of different object types. The
objects are the graphics data structures. The types of objects are:
<code>figure</code>, <code>axes</code>, <code>line</code>, <code>text</code>, <code>patch</code>,
<code>surface</code>, <code>text</code> and <code>image</code>.
</p>
<p>Each of these objects has a function by the same name. and, each of these
functions returns a graphics handle pointing to an object of corresponding
type. In addition there are several functions which operate on properties of
the graphics objects and which return handles: the functions <code> plot</code> and
<code>plot3</code> return a handle pointing to an object of type line, the function
<code>subplot</code> returns a handle pointing to an object of type axes, the
function <code>fill</code> returns a handle pointing to an object of type patch, the
functions <code>area</code>, <code>bar</code>, <code>barh</code>, <code>contour</code>,
<code>contourf</code>, <code>contour3</code>, <code>surf</code>, <code>mesh</code>, <code>surfc</code>,
<code>meshc</code>, <code>errorbar</code>, <code>quiver</code>, <code>quiver3</code>, <code>scatter</code>,
<code>scatter3</code>, <code>stair</code>, <code>stem</code>, <code>stem3</code> each return a handle
as documented in <a href="Data-Sources-in-Object-Groups.html#XREFdatasources">Data Sources</a>.
</p>
<p>The graphics objects are arranged in a hierarchy:
</p>
<p>1. The root is at 0. i.e., <code>get (0)</code> returns the properties of the root
object.
</p>
<p>2. Below the root are <code>figure</code> objects.
</p>
<p>3. Below the <code>figure</code> objects are <code>axes</code>.
</p>
<p>4. Below the <code>axes</code> objects are
<code>line</code>, <code>text</code>, <code>patch</code>,
<code>surface</code>, and <code>image</code> objects.
</p>
<p>Graphics handles may be distinguished from function handles
(see <a href="Function-Handles.html#Function-Handles">Function Handles</a>) by means of the function <code>ishandle</code>.
<code>ishandle</code> returns true if its argument is a handle of a graphics object.
In addition, the figure object may be tested using <code>isfigure</code>.
<code>isfigure</code> returns true only if its argument is a handle of a figure. The
<code>whos</code> function can be used to show the object type of each currently
defined graphics handle. (Note: this is not true today, but it is, I hope,
considered an error in whos. It may be better to have whos just show
graphics_handle as the class, and provide a new function which, given a
graphics handle, returns its object type. This could generalize the ishandle()
functions and, in fact, replace them.)
</p>
<p>The <code>get</code> and <code>set</code> commands are used to obtain and set the values of
properties of graphics objects. In addition, the <code>get</code> command may be
used to obtain property names.
</p>
<p>For example, the property <code>"type"</code> of the graphics object pointed to by
the graphics handle h may be displayed by:
</p>
<div class="example">
<pre class="example">get (h, "type")
</pre></div>
<p>The properties and their current values are returned by <code>get (h)</code>
where h is a handle of a graphics object. If only the names of the
allowed properties are wanted they may be displayed by:
<code>get (h, "")</code>.
</p>
<p>Thus, for example:
</p>
<div class="smallexample">
<pre class="smallexample">h = figure ();
get (h, "type")
ans = figure
get (h, "");
error: get: ambiguous figure property name ; possible matches:
__enhanced__ hittest resize
__graphics_toolkit__ integerhandle resizefcn
__guidata__ interruptible selected
__modified__ inverthardcopy selectionhighlight
__myhandle__ keypressfcn selectiontype
__plot_stream__ keyreleasefcn tag
alphamap menubar toolbar
beingdeleted mincolormap type
busyaction name uicontextmenu
buttondownfcn nextplot units
children numbertitle userdata
clipping outerposition visible
closerequestfcn paperorientation windowbuttondownfcn
color paperposition windowbuttonmotionfcn
colormap paperpositionmode windowbuttonupfcn
createfcn papersize windowkeypressfcn
currentaxes papertype windowkeyreleasefcn
currentcharacter paperunits windowscrollwheelfcn
currentobject parent windowstyle
currentpoint pointer wvisual
deletefcn pointershapecdata wvisualmode
dockcontrols pointershapehotspot xdisplay
doublebuffer position xvisual
filename renderer xvisualmode
handlevisibility renderermode
</pre></div>
<p>The root figure has index 0. Its properties may be displayed by:
<code>get (0, "")</code>.
</p>
<p>The uses of <code>get</code> and <code>set</code> are further explained in
<a href="Graphics-Objects.html#XREFget">get</a>, <a href="Graphics-Objects.html#XREFset">set</a>.
</p>
<a name="XREFisprop"></a><dl>
<dt><a name="index-isprop"></a>Function File: <em><var>res</var> =</em> <strong>isprop</strong> <em>(<var>h</var>, "<var>prop</var>")</em></dt>
<dd><p>Return true if <var>prop</var> is a property of the object with handle <var>h</var>.
</p>
<p><var>h</var> may also be an array of handles in which case <var>res</var> will be a
logical array indicating whether each handle has the property <var>prop</var>.
</p>
<p><strong>See also:</strong> <a href="Graphics-Objects.html#XREFget">get</a>, <a href="Graphics-Objects.html#XREFset">set</a>, <a href="Creating-a-Class.html#XREFismethod">ismethod</a>, <a href="Creating-a-Class.html#XREFisobject">isobject</a>.
</p></dd></dl>
<hr>
<div class="header">
<p>
Next: <a href="Graphics-Objects.html#Graphics-Objects" accesskey="n" rel="next">Graphics Objects</a>, Up: <a href="Graphics-Data-Structures.html#Graphics-Data-Structures" accesskey="u" rel="up">Graphics Data Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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