Next: Graphics Object Properties, Previous: Introduction to Graphics Structures, Up: Graphics Data Structures [Contents][Index]
The hierarchy of graphics objects was explained above. See Introduction to Graphics Structures. Here the specific objects are described, and the properties contained in these objects are discussed. Keep in mind that graphics objects are always referenced by handle.
the top level of the hierarchy and the parent of all figure objects. The handle index of the root figure is 0.
A figure window.
A set of axes. This object is a child of a figure object and may be a parent of line, text, image, patch, surface, or light objects.
A line in two or three dimensions.
Text annotations.
A bitmap image.
A filled polygon, currently limited to two dimensions.
A three-dimensional surface.
A light object used for lighting effects on patches and surfaces.
You can create any graphics object primitive by calling the function of the
same name as the object; In other words, figure
, axes
,
line
, text
, image
, patch
, surface
, and
light
functions. These fundamental graphic objects automatically become
children of the current axes object as if hold on
was in place.
Separately, axes will automatically become children of the current figure
object and figures will become children of the root object 0.
If this auto-joining feature is not desired then it is important to call
newplot
first to prepare a new figure and axes for plotting.
Alternatively, the easier way is to call a high-level graphics routine which
will both create the plot and then populate it with low-level graphics objects.
Instead of calling line
, use plot
. Or use surf
instead of
surface
. Or use fill
instead of patch
.
Create an axes object and return a handle to it, or set the current axes to hax.
Called without any arguments, or with property/value pairs, construct a new axes. For accepted properties and corresponding values, see set.
Called with a single axes handle argument hax, the function makes hax the current axes. It also restacks the axes in the corresponding figure so that hax is the first entry in the list of children. This causes hax to be displayed on top of any other axes objects (Z-order stacking).
Create line object from x and y (and possibly z) and insert in the current axes.
Multiple property-value pairs may be specified for the line object, but they must appear in pairs.
If the first argument hax is an axes handle, then plot into this axes,
rather than the current axes returned by gca
.
The optional return value h is a graphics handle (or vector of handles) to the line objects created.
Create patch object in the current axes with vertices at locations (x, y) and of color c.
If the vertices are matrices of size MxN then each polygon patch has M vertices and a total of N polygons will be created. If some polygons do not have M vertices use NaN to represent "no vertex". If the z input is present then 3-D patches will be created.
The color argument c can take many forms. To create polygons
which all share a single color use a string value (e.g., "r"
for
red), a scalar value which is scaled by caxis
and indexed into the
current colormap, or a 3-element RGB vector with the precise TrueColor.
If c is a vector of length N then the ith polygon will have a color
determined by scaling entry c(i) according to caxis
and then
indexing into the current colormap. More complicated coloring situations
require directly manipulating patch property/value pairs.
Instead of specifying polygons by matrices x and y, it is
possible to present a unique list of vertices and then a list of polygon
faces created from those vertices. In this case the
"Vertices"
matrix will be an Nx2 (2-D patch) or
Nx3 (3-D patch). The MxN "Faces"
matrix
describes M polygons having N vertices—each row describes a
single polygon and each column entry is an index into the
"Vertices"
matrix to identify a vertex. The patch object
can be created by directly passing the property/value pairs
"Vertices"
/verts, "Faces"
/faces as
inputs.
Instead of using property/value pairs, any property can be set by passing a structure propstruct with the respective field names.
If the first argument hax is an axes handle, then plot into this axes,
rather than the current axes returned by gca
.
The optional return value h is a graphics handle to the created patch object.
Implementation Note: Patches are highly configurable objects. To truly
customize them requires setting patch properties directly. Useful patch
properties are: "cdata"
, "edgecolor"
,
"facecolor"
, "faces"
, "facevertexcdata"
.
Create a surface graphic object given matrices x and y from
meshgrid
and a matrix of values z corresponding to the
x and y coordinates of the surface.
If x and y are vectors, then a typical vertex is
(x(j), y(i), z(i,j)). Thus, columns of z correspond
to different x values and rows of z correspond to different
y values. If only a single input z is given then x is
taken to be 1:columns (z)
and y is
1:rows (z)
.
Any property/value input pairs are assigned to the surface object.
If the first argument hax is an axes handle, then plot into this axes,
rather than the current axes returned by gca
.
The optional return value h is a graphics handle to the created surface object.
Create a light object in the current axes or for axes hax.
When a light object is present in an axes object, and the properties
"EdgeLighting"
or "FaceLighting"
of a patch
or
surface
object are set to a value other than "none"
, these
objects are drawn with light and shadow effects. Supported values for
Lighting properties are "none"
(no lighting effects), "flat"
(faceted look of the objects), and "gouraud"
(linear interpolation
of the lighting effects between the vertices). For patch
objects,
the normals must be set manually (property "VertexNormals"
).
Up to eight light objects are supported per axes.
Lighting is only supported for OpenGL graphic toolkits (i.e., "fltk"
and "qt"
).
A light object has the following properties which alter the appearance of the plot.
"Color":
The color of the light can be passed as anRGB-vector (e.g., [1 0 0]
for red) or as a string (e.g., "r"
for red). The default color is white ([1 1 1]
).
"Position":
The direction from which the light emanates as a1x3-vector. The default direction is [1 0 1]
.
"Style":
This string defines whether the light emanates from alight source at infinite distance ("infinite"
) or from a local point
source ("local"
). The default is "infinite"
.
If the first argument hax is an axes handle, then add the light object
to this axes, rather than the current axes returned by gca
.
The optional return value h is a graphics handle to the created light object.
To determine whether a variable is a graphics object index, or an index
to an axes or figure, use the functions ishandle
, isaxes
, and
isfigure
.
Return true if h is a graphics handle and false otherwise.
h may also be a matrix of handles in which case a logical array is returned that is true where the elements of h are graphics handles and false where they are not.
Return true if h is a graphics handle (of type type) and false otherwise.
When no type is specified the function is equivalent to
ishandle
.
See also: ishandle.
Return true if h is an axes graphics handle and false otherwise.
If h is a matrix then return a logical array which is true where the elements of h are axes graphics handles and false where they are not.
Return true if h is a figure graphics handle and false otherwise.
If h is a matrix then return a logical array which is true where the elements of h are figure graphics handles and false where they are not.
The function gcf
returns an index to the current figure object,
or creates one if none exists. Similarly, gca
returns the
current axes object, or creates one (and its parent figure object) if
none exists.
Return a handle to the current figure.
The current figure is the default target for graphics output. If multiple
figures exist, gcf
returns the last created figure or the last figure
that was clicked on with the mouse.
If a current figure does not exist, create one and return its handle. The handle may then be used to examine or set properties of the figure. For example,
fplot (@sin, [-10, 10]); fig = gcf (); set (fig, "numbertitle", "off", "name", "sin plot")
plots a sine wave, finds the handle of the current figure, and then renames the figure window to describe the contents.
Note: To find the current figure without creating a new one if it does not
exist, query the "CurrentFigure"
property of the root graphics
object.
get (0, "currentfigure");
Return a handle to the current axes object.
The current axes is the default target for graphics output. In the case
of a figure with multiple axes, gca
returns the last created axes
or the last axes that was clicked on with the mouse.
If no current axes object exists, create one and return its handle. The handle may then be used to examine or set properties of the axes. For example,
ax = gca (); set (ax, "position", [0.5, 0.5, 0.5, 0.5]);
creates an empty axes object and then changes its location and size in the figure window.
Note: To find the current axes without creating a new axes object if it
does not exist, query the "CurrentAxes"
property of a figure.
get (gcf, "currentaxes");
Return a handle to the current object of the current figure, or a handle to the current object of the figure with handle fig.
The current object of a figure is the object that was last clicked on. It
is stored in the "CurrentObject"
property of the target figure.
If the last mouse click did not occur on any child object of the figure, then the current object is the figure itself.
If no mouse click occurred in the target figure, this function returns an empty matrix.
Programming Note: The value returned by this function is not necessarily the
same as the one returned by gcbo
during callback execution. An
executing callback can be interrupted by another callback and the current
object may be changed.
The get
and set
functions may be used to examine and set
properties for graphics objects. For example,
get (0) ⇒ ans = { type = root currentfigure = [](0x0) children = [](0x0) visible = on … }
returns a structure containing all the properties of the root figure.
As with all functions in Octave, the structure is returned by value, so
modifying it will not modify the internal root figure plot object. To
do that, you must use the set
function. Also, note that in this
case, the currentfigure
property is empty, which indicates that
there is no current figure window.
The get
function may also be used to find the value of a single
property. For example,
get (gca (), "xlim") ⇒ [ 0 1 ]
returns the range of the x-axis for the current axes object in the current figure.
To set graphics object properties, use the set function. For example,
set (gca (), "xlim", [-10, 10]);
sets the range of the x-axis for the current axes object in the current figure to ‘[-10, 10]’.
Default property values can also be queried if the set
function is
called without a value argument. When only one argument is given (a graphic
handle) then a structure with defaults for all properties of the given object
type is returned. For example,
set (gca ())
returns a structure containing the default property values for axes objects.
If set
is called with two arguments (a graphic handle and a property
name) then only the defaults for the requested property are returned.
Return the value of the named property p from the graphics handle h.
If p is omitted, return the complete property list for h.
If h is a vector, return a cell array including the property values or lists respectively.
See also: set.
Set named property values for the graphics handle (or vector of graphics handles) h.
There are three ways to give the property names and values:
Here, each property is a string containing the property name, each value is a value of the appropriate type for the property.
In this case, the number of columns of values must match the number of elements in properties. The first column of values contains values for the first entry in properties, etc. The number of rows of values must be 1 or match the number of elements of h. In the first case, each handle in h will be assigned the same values. In the latter case, the first handle in h will be assigned the values from the first row of values and so on.
Here, the field names of pv represent the property names, and the field values give the property values. In contrast to the previous case, all elements of pv will be set in all handles in h independent of the dimensions of pv.
set
is also used to query the list of values a named property will
take. clist = set (h, "property")
will return the list
of possible values for "property"
in the cell list clist.
If no output variable is used then the list is formatted and printed to the
screen.
If no property is specified (slist = set (h)
) then a
structure slist is returned where the fieldnames are the properties of
the object h and the fields are the list of possible values for each
property. If no output variable is used then the list is formatted and
printed to the screen.
For example,
hf = figure (); set (hf, "paperorientation") ⇒ paperorientation: [ landscape | {portrait} | rotated ]
shows the paperorientation property can take three values with the default
being "portrait"
.
See also: get.
Return the first ancestor of handle object h whose type matches type, where type is a character string.
If type is a cell array of strings, return the first parent whose type matches any of the given type strings.
If the handle object h itself is of type type, return h.
If "toplevel"
is given as a third argument, return the highest
parent in the object hierarchy that matches the condition, instead
of the first (nearest) one.
Find all children, including hidden children, of a graphics object.
This function is similar to get (h, "children")
, but also returns
hidden objects (HandleVisibility = "off"
).
If handles is a scalar, h will be a vector. Otherwise, h will be a cell matrix of the same size as handles and each cell will contain a vector of handles.
Find all visible figures that are currently off the screen and move them onto the screen.
Figures can be printed or saved in many graphics formats with print
and
saveas
. Occasionally, however, it may be useful to save the original
Octave handle graphic directly so that further modifications can be made such
as modifying a title or legend.
This can be accomplished with the following functions by
fig_struct = hdl2struct (gcf); save myplot.fig -struct fig_struct; … fig_struct = load ("myplot.fig"); struct2hdl (fig_struct);
Return a structure, s, whose fields describe the properties of the object, and its children, associated with the handle, h.
The fields of the structure s are "type"
, "handle"
,
"properties"
, "children"
, and "special"
.
See also: struct2hdl, hgsave, findobj.
Construct a graphics handle object h from the structure s.
The structure must contain the fields "handle"
, "type"
,
"children"
, "properties"
, and "special"
.
If the handle of an existing figure or axes is specified, p, the new object will be created as a child of that object. If no parent handle is provided then a new figure and the necessary children will be constructed using the default values from the root figure.
A third boolean argument hilev can be passed to specify whether the function should preserve listeners/callbacks, e.g., for legends or hggroups. The default is false.
See also: hdl2struct, hgload, findobj.
Construct a copy of the graphic objects associated with the handles horig and return new handles hnew to the new objects.
If a parent handle hparent (root, figure, axes, or hggroup) is specified, the copied object will be created as a child of hparent.
If horig is a vector of handles, and hparent is a scalar,
then each handle in the vector hnew has its "Parent"
property
set to hparent. Conversely, if horig is a scalar and
hparent a vector, then each parent object will receive a copy of
horig. If horig and hparent are both vectors with the
same number of elements then hnew(i)
will have parent
hparent(i)
.
See also: struct2hdl, hdl2struct, findobj.
Next: Graphics Object Properties, Previous: Introduction to Graphics Structures, Up: Graphics Data Structures [Contents][Index]