WIDGET_BUTTON

Buttons placed into exclusive or non-exclusive bases (created via the EXCLUSIVE or NONEXCLUSIVE keywords to WIDGET_BASE function) are created as two-state "toggle" buttons, which are controlled by such bases.

Bitmap Button Labels

Widget buttons can have either a text label (specified as a string value to the VALUE keyword) or a graphic symbol in the form of a bitmap. Bitmap labels are specified in one of the following ways:

By setting the VALUE keyword equal to a string containing the name of an image file in BMP format, and setting the BITMAP keyword:

button=WIDGET_BUTTON(base, VALUE='mybitmap.bmp', /BITMAP)

For 16- and 256-color bitmap files, IDL uses the color of the pixel in the lower left corner as the transparent color. All pixels of this color become transparent, allowing the button color to show through.

To modify the bitmap after creation, use the /BITMAP keyword with WIDGET_CONTROL:

WIDGET_CONTROL, button, SET_VALUE='mybitmap2.bmp', /BITMAP

By setting the VALUE keyword equal to an n x m bitmap byte array in which each bit represents a pixel with a value of either zero or one. (Arrays of this type can be produced using the CVTTOBM function.) This method creates a black-and-white bitmap label:

button=WIDGET_BUTTON(base, VALUE=bw_arr) 
 
To modify the bitmap after creation, simply set a new value using WIDGET_CONTROL:


WIDGET_CONTROL, button, SET_VALUE=bw_array2

By setting the VALUE keyword equal to an n x m x 3 byte array that represents a 24-bit color image, interleaved by plane, with the planes in the order red, green, blue. This method creates a color bitmap label:

button=WIDGET_BUTTON(base, VALUE=color_array)

To modify the bitmap after creation, simply set a new value using WIDGET_CONTROL:

WIDGET_CONTROL, button, SET_VALUE=color_array2

See Using Button Widgets for additional details on creating image files and arrays for use as button bitmaps.

Syntax

Result = WIDGET_BUTTON( Parent [, /ALIGN_CENTER | , /ALIGN_LEFT | , /ALIGN_RIGHT] [, /BITMAP] [, /CHECKED_MENU] [, /DYNAMIC_RESIZE] [, EVENT_FUNC=string] [, EVENT_PRO=string] [, FONT=string] [, FRAME=width] [, FUNC_GET_VALUE=string] [, GROUP_LEADER=widget_id] [, /HELP] [, KILL_NOTIFY=string] [, /MENU] [, /NO_COPY] [, /NO_RELEASE] [, NOTIFY_REALIZE=string] [, PRO_SET_VALUE=string] [, /PUSHBUTTON_EVENTS] [, SCR_XSIZE=width] [, SCR_YSIZE=height] [, /SENSITIVE] [, /SEPARATOR] [, TOOLTIP=string] [, /TRACKING_EVENTS] [, UNAME=string] [, UNITS={0 | 1 | 2}] [, UVALUE=value] [, VALUE=value] [, X_BITMAP_EXTRA=bits] [, XOFFSET=value] [, XSIZE=value] [, YOFFSET=value] [, YSIZE=value] )

Return Value

The returned value of this function is the widget ID of the newly-created button.

Arguments

Parent

Keywords

ALIGN_CENTER

ALIGN_LEFT

ALIGN_RIGHT

BITMAP

Set this keyword to specify that the bitmap specified with the VALUE keyword is a color bitmap. The value of a widget button can be a bitmap as described in Bitmap Button Labels. If you specify a color bitmap with the VALUE keyword, you must also set the /BITMAP keyword.

CHECKED_MENU

Set this keyword on a menu entry button to enable the ability to place a check (Windows) or selection box (Motif) next to the menu entry. The parent widget of the button must be either a button widget created with the MENU keyword or a base widget created with the CONTEXT_MENU keyword.

On Windows systems, a menu item that has the checked menu feature enabled but which is unselected appears just like a "normal" menu item. On Motif systems, a menu item that has the checked menu feature enabled always displays a selection box, even if the box is not selected.

DYNAMIC_RESIZE

Set this keyword to create a widget that resizes itself to fit its new value whenever its value is changed. Note that this keyword does not take effect when used with the SCR_XSIZE, SCR_YSIZE, XSIZE, or YSIZE keywords. If one of these keywords is also set, the widget will be sized as specified by the sizing keyword and will never resize itself dynamically.

EVENT_FUNC

A string containing the name of a function to be called by the WIDGET_EVENT function when an event arrives from a widget in the widget hierarchy rooted at the newly-created widget.

EVENT_PRO

A string containing the name of a procedure to be called by the WIDGET_EVENT function when an event arrives from a widget in the widget hierarchy rooted at the newly-created widget.

FONT

The name of the font to be used by the widget. The font specified is a "device font" (an X Windows font on Motif systems; a TrueType or PostScript font on Windows systems). See About Device Fonts for details on specifying names for device fonts. If this keyword is omitted, the default font is used.

FRAME

The value of this keyword specifies the width of a frame in units specified by the UNITS keyword (pixels are the default) to be drawn around the borders of the widget. Note that this keyword is only a "hint" to the toolkit, and may be ignored in some instances.

FUNC_GET_VALUE

A string containing the name of a function to be called when the GET_VALUE keyword to the WIDGET_CONTROL procedure is called for this widget. Using this technique allows you to change the value that should be returned for a widget. Compound widgets use this ability to define their values transparently to the user.

GROUP_LEADER

The widget ID of an existing widget that serves as "group leader" for the newly-created widget. When a group leader is killed, for any reason, all widgets in the group are also destroyed.

A given widget can be in more than one group. The WIDGET_CONTROL procedure can be used to add additional group associations to a widget. It is not possible to remove a widget from an existing group.

HELP

Set this keyword to tell the widget toolkit that this button is a "help" button for a menubar and should be given that appearance. For example, Motif specifies that the help menubar item is displayed on the far right of the menubar. This keyword is ignored in all other contexts and may be ignored by window managers that have no such special appearance defined.

KILL_NOTIFY

Set this keyword to a string that contains the name of a procedure to be called automatically when the specified widget dies. Each widget is allowed a single such "callback" procedure. It can be removed by setting the routine to the null string ('').

The callback routine is called with the widget identifier as its only argument. At that point, the widget identifier can only be used with the WIDGET_CONTROL procedure to get or set the user value. All other requests that require a widget ID are disallowed for the target widget. The callback is not issued until the WIDGET_EVENT function is called.

The presence of this keyword indicates that the button will be used to activate a pull-down menu. Such buttons can have button children that are then placed into a pull-down menu.

Under Motif, if the value specified for MENU is greater than 1, the button label is enclosed in a box to indicate that this button is a pull-down menu. See the CW_PDMENU function for a high-level pull-down menu creation utility.

NO_COPY

Usually, when setting or getting widget user values, either at widget creation or using the SET_UVALUE and GET_UVALUE keywords to WIDGET_CONTROL, IDL makes a second copy of the data being transferred. Although this technique is fine for small data, it can have a significant memory cost when the data being copied is large.

If the NO_COPY keyword is set, IDL handles these operations differently. Rather than copy the source data, it takes the data away from the source and attaches it directly to the destination. This feature can be used by compound widgets to obtain state information from a UVALUE without all the memory copying that would otherwise occur. However, it has the side effect of causing the source variable to become undefined. On a "set" operation (using the UVALUE keyword to WIDGET_BUTTON or the SET_UVALUE keyword to WIDGET_CONTROL), the variable passed as value becomes undefined. On a "get" operation (GET_UVALUE keyword to WIDGET_CONTROL), the user value of the widget in question becomes undefined.

NO_RELEASE

Set this keyword to make exclusive and non-exclusive buttons generate only select events. This keyword has no effect on regular buttons.

NOTIFY_REALIZE

Set this keyword to a string that contains the name of a procedure to be called automatically when the specified widget is realized. This callback occurs just once (because widgets are realized only once). Each widget is allowed a single such "callback" procedure. It can be removed by setting the routine to the null string (''). The callback routine is called with the widget ID as its only argument.

PRO_SET_VALUE

A string containing the name of a procedure to be called when the SET_VALUE keyword to the WIDGET_CONTROL procedure is called for this widget. Using this technique allows you to designate a routine that sets the value for a widget. Compound widgets use this ability to define their values transparently to the user.

PUSHBUTTON_EVENTS

Set this keyword to cause separate button events to be issued for the widget when the left mouse button is pressed and released, or when the spacebar is pressed and released.

When this keyword is not set and the button is selected, pressing and releasing either the left mouse button or the spacebar generates a single button event, with the SELECT field set equal to 1. When this keyword is set:

Pressing the left mouse button generates a button event with the SELECT field set equal to 1.

Releasing the left mouse button generates a button event with the SELECT field set equal to 0.

Pressing the spacebar generates a button event with the SELECT field set equal to 1 immediately followed by a second button event with the SELECT field set equal to 0.

Pressing and holding the spacebar generates a series of button events, with the value of the SELECT field alternating between 1 and 0. The rate at which events are generated is governed by the key-repeat settings of the operating system.

RESOURCE_NAME

A string containing an X Window System resource name to be applied to the widget. See RESOURCE_NAME for a complete discussion of this keyword.

SCR_XSIZE

Set this keyword to the desired "screen" width of the widget, in units specified by the UNITS keyword (pixels are the default). In many cases, setting this keyword is the same as setting the XSIZE keyword.

SCR_YSIZE

Set this keyword to the desired "screen" height of the widget, in units specified by the UNITS keyword (pixels are the default). In many cases, setting this keyword is the same as setting the YSIZE keyword.

SENSITIVE

If SENSITIVE is zero, the widget becomes insensitive. If nonzero, it becomes sensitive. When a widget is sensitive, it has normal appearance and can receive user input. For example, a sensitive button widget can be activated by moving the mouse cursor over it and pressing a mouse button. When a widget is insensitive, it indicates the fact by changing its appearance, looking disabled, and it ignores any input.

Sensitivity can be used to control when a user is allowed to manipulate the widget. Note that some widgets do not change their appearance when they are made insensitive, but they cease generating events.

After creating the widget hierarchy, you can change the sensitivity state using the SENSITIVE keyword with the WIDGET_CONTROL procedure.

SEPARATOR

Set this keyword to tell the widget toolkit that this button is part of a pulldown menu pane and that a separator line should be added directly above this entry. This keyword is ignored in all other contexts.

TOOLTIP

Set this keyword to a string that will be displayed when the cursor hovers over the widget. For UNIX platforms, this string must be non-zero in length.

TRACKING_EVENTS

Set this keyword to cause widget tracking events to be issued for the widget whenever the mouse pointer enters or leaves the region covered by that widget. For the structure of tracking events, see TRACKING_EVENTS in the documentation for WIDGET_BASE.

UNAME

Set this keyword to a string that can be used to identify the widget in your code. You can associate a name with each widget in a specific hierarchy, and then use that name to query the widget hierarchy and get the correct widget ID.

To query the widget hierarchy, use the WIDGET_INFO function with the FIND_BY_UNAME keyword. The UNAME should be unique to the widget hierarchy because the FIND_BY_UNAME keyword returns the ID of the first widget with the specified name.

UNITS

Set UNITS equal to 0 (zero) to specify that all measurements are in pixels (this is the default), to 1 (one) to specify that all measurements are in inches, or to 2 (two) to specify that all measurements are in centimeters.

UVALUE

Each widget can contain a user-specified value of any data type and organization. This value is not used by the widget in any way, but exists entirely for the convenience of the IDL programmer. This keyword allows you to set this value when the widget is first created.

VALUE

The initial value setting of the widget. The value of a widget button is the label for that button. You can set VALUE to any of the following:

a string value, which displays as text;

an n x m byte array, which displays as a black-and-white bitmap image;

an n x m x 3 byte array, which displays as a 24-bit color bitmap image;

if the BITMAP keyword is also specified, the name of a bitmap image file that displays as a color bitmap image of the same depth as the image in the file.

See Bitmap Button Labels for additional details on using bitmap images as button labels.

X_BITMAP_EXTRA

When creating a bitmap button that is not of a "byte-aligned" size (i.e., a dimension is not a multiple of 8), this keyword specifies how many bits of the supplied bitmap must be ignored (within the end byte). For example, to create a 10 by 8 bitmap, you need to supply a 2 by 8 array of bytes and ignore the bottom 6 bits. Therefore, you would specify X_BITMAP_EXTRA = 6.

XOFFSET

The horizontal offset of the widget in units specified by the UNITS keyword (pixels are the default) relative to its parent.

Specifying an offset relative to a row or column major base widget does not work because those widgets enforce their own layout policies. This keyword is primarily of use relative to a plain base widget. Note that it is best to avoid using this style of widget programming.

XSIZE

The width of the widget in units specified by the UNITS keyword (pixels are the default). Most widgets attempt to size themselves to fit the situation. However, if the desired effect is not produced, use this keyword to override it. This keyword is only a "hint" to the toolkit and may be ignored in some situations.

YOFFSET

The vertical offset of the widget in units specified by the UNITS keyword (pixels are the default) relative to its parent. This offset is specified relative to the upper left corner of the parent widget.

YSIZE

The height of the widget in units specified by the UNITS keyword (pixels are the default). Most widgets attempt to size themselves to fit the situation. However, if the desired effect is not produced, use this keyword to override it. This keyword is only a "hint" to the toolkit and may be ignored in some situations.

Keywords to WIDGET_CONTROL

Keywords to WIDGET_INFO

Some keywords to the WIDGET_INFO function return information that applies specifically to button widgets. In addition to those keywords that apply to all widgets, the following are particularly useful: BUTTON_SET, DYNAMIC_RESIZE, PUSHBUTTON_EVENTS, TOOLTIP.

Events Returned by Button Widgets

Pressing the mouse button while the mouse cursor is over a button widget causes the widget to generate an event. The event structure returned by the WIDGET_EVENT function is defined by the following statement:

ID is the widget id of the button generating the event. TOP is the widget ID of the top level widget containing ID. HANDLER contains the widget ID of the widget associated with the handler routine. SELECT is set to 1 if the button was set, and 0 if released. Unless the PUSHBUTTON_EVENTS keyword is set, normal buttons do not generate events when released, so SELECT will always be 1. Toggle buttons (children of either an exclusive or non-exclusive base) always return separate events for the set and release actions.