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<a name="Introduction-to-Graphics-Structures"></a>
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<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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<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 visual display. A
graphics handle may point to any one of a number of different base object
types and these objects are the graphics data structures themselves. The
primitive graphic object types are: <code>figure</code>, <code>axes</code>, <code>line</code>,
<code>text</code>, <code>patch</code>, <code>surface</code>, <code>text</code>, <code>image</code>, and
<code>light</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 the corresponding
type. In addition there are several functions which operate on properties of
the graphics objects and which also 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
to a complex data structure 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 object is returned by <code>groot</code> (historically, equivalent to
the handle 0). In other words, <code>get (groot)</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> or <code>hggroup</code> objects.
</p>
<p>4. Below the <code>axes</code> objects are <code>line</code>, <code>text</code>, <code>patch</code>,
<code>surface</code>, <code>image</code>, and <code>light</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>ishghandle</code>.
<code>ishghandle</code> returns true if its argument is a handle of a graphics
object. In addition, a figure or axes object may be tested using
<code>isfigure</code> or <code>isaxes</code> respectively. To test for a specific type of
graphics handle, such as a patch or line object, use <code>isgraphics</code>. The
more specific test functions return true only if the argument is both a
graphics handle and of the correct type (figure, axes, specified object type).
</p>
<p>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:
__gl_extensions__ dockcontrols renderer
__gl_renderer__ doublebuffer renderermode
__gl_vendor__ filename resize
__gl_version__ graphicssmoothing resizefcn
__graphics_toolkit__ handlevisibility selected
__guidata__ hittest selectionhighlight
__modified__ integerhandle selectiontype
__mouse_mode__ interruptible sizechangedfcn
__myhandle__ inverthardcopy tag
__pan_mode__ keypressfcn toolbar
__plot_stream__ keyreleasefcn type
__rotate_mode__ menubar uicontextmenu
__zoom_mode__ mincolormap units
alphamap name userdata
beingdeleted nextplot visible
busyaction numbertitle windowbuttondownfcn
buttondownfcn outerposition windowbuttonmotionfcn
children paperorientation windowbuttonupfcn
clipping paperposition windowkeypressfcn
closerequestfcn paperpositionmode windowkeyreleasefcn
color papersize windowscrollwheelfcn
colormap papertype windowstyle
createfcn paperunits wvisual
currentaxes parent wvisualmode
currentcharacter pointer xdisplay
currentobject pointershapecdata xvisual
currentpoint pointershapehotspot xvisualmode
deletefcn position
</pre></div>
<p>The properties of the root figure may be displayed by:
<code>get (groot, "")</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><em><var>res</var> =</em> <strong>isprop</strong> <em>(<var>obj</var>, "<var>prop</var>")</em></dt>
<dd><p>Return true if <var>prop</var> is a property of the object <var>obj</var>.
</p>
<p><var>obj</var> may also be an array of objects in which case <var>res</var> will be a
logical array indicating whether each handle has the property <var>prop</var>.
</p>
<p>For plotting, <var>obj</var> is a handle to a graphics object. Otherwise,
<var>obj</var> should be an instance of a class.
</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>
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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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