Programmer Guide/Shell Items/Graph/Introducing Graph Items

Graph Item
INTRODUCTION	NEW	SET	ATTRIBUTES	MESSAGES	EXAMPLES

The STx graph item is used to plot data on screen. Currently the following plot types are supported:

• spectrum
• parameter
• waveform
• spectrogram
• waterfall

The graph item also implements graphical cursors which can be used to extract values from the data via visual positioning, and segments to mark an area of the graph with text and coloured shapes.

Note that you cannot display a graph item without a display item (you need to specify the display on graph creation).

Plot Types

STx supports the following plot types:

Spectrum Plot

Parameter Plot

Waveform Plot

Spectrogram Plot

Waterfall Plot

Cursors

STx supports two cursors which the user can position within the graph using the mouse or the keyboard.

Cursor Selection

By default, neither cursor is selected. A selected cursor is displayed in a different colour on screen and the index of the selected cursor can be retrieved programmatically. Only one of the graph's cursors can be selected at any one time. If the user clicks on a cursor, that cursor is selected. If the user clicks on the graph itself, the selected cursor is deselected.

Note that you can select and deselect a cursor using the CURSORPOS command.

A message is sent to the graph when a cursor is selected or deselected.

Connecting a Value Item to a Cursor

In order to extract the cursor position, the cursor must be connected to a value item. This is done by specifying the graph's cursor output as the value item's input:

#cursorInfo := new value *
$#cursorInfo input $#graph.cursors /Read

Reading Cursor Values

Once a cursor has been attached to a value item, the values of the cursors can be accessed via the value item's !DATA attribute:

// retrieve the x and y value of the first cursor (cursor 1)
#x := $#cursorInfo[!data,5]
#y := $#cursorInfo[!data,6]

Cursor Status Value Item Vector

The value item's !DATA attribute has the following 20 indices defined for cursor status information:

index	description
0	index of selected cursor (1 or 2) or 0 if no cursor is selected
1	index (>=0) of function if cursor is bound and <0 if not bound
2	control command code (*). 1 if the control key is pressed, 2 if the shift key is pressed, 3 if both control and shift are pressed, 0 otherwise
3	not used
4	cursor style (index)
5/10	x position of first (5) and second (10) cursor
6/11	y position of first (6) and second (11) cursor
7/12	index of function value addressed by first (7) and second (12) cursor (only if function bound)
8/13	not used
8/14	not used
15	x position of control command (*)
16	y position of control command (*)
17-19	not used

(*) A control command is sent when the control or shift key is held and the left mouse button is pressed inside the graphs draw region. This feature was implemented for real-time tagging in the Recorder application

Setting Cursor Positions

A cursor position can be set programmatically using the graph command SET graph CURSORPOS.