Screen Class

The Screen class assists the mapping of protocols which represent screens of information to the user -- such as Videotex. Data received down a comms line can be put on the screen and then analysed.

Triggers can be set up on the screen which fire when their trigger-conditions are satisfied. The list of available trigger types is as follows:

`home`	the 'home' character is received
`reset`	the 'reset' character is received
`cursorOn`	the 'cursor-on' character is received
`cursorOff`	the 'cursor-off' character is received
`hotText`	the supplied text appears at the given position on screen
`hotPatch`	the cursor enters the supplied region of the screen
`exitZone`	the cursor leaves the supplied region of the screen
`messageRow`	a message appears on the supplied row of the screen

Screen Creation

The create function can be used to create a Screen object of a given no. of rows and columns e.g.

    (create Screen 24 40)

Once created, this module is tailored using its properties and methods.

Screen Properties

A Screen object supports the following properties:

property name	property type	description
`row`	`Integer`	current display row (0 based)
`column`	`Integer`	current display column (0 based)
`nRows`	`Integer`	number of rows on the screen
`nColumns`	`Integer`	number of columns on the screen
`carriageReturnChar`	`Integer`	character used as the 'carriage return' character to go to the start of the row
`lineFeedChar`	`Integer`	character used as the 'line-feed' character to go down a row
`homeChar`	`Integer`	character used as the 'home' character to go to the initial row and column without changing the screen contents
`resetChar`	`Integer`	character used as the 'reset' character to go to the initial row and column and clearing the screen
`cursorOnChar`	`Integer`	character used as the 'cursor-on' character which turns on the display of the cursor
`cursorOffChar`	`Integer`	character used as the 'cursor-off' character which turns off the display of the cursor
`escapeChar`	`Integer`	character used as the 'escape' character which makes the following character have a special meaning
`verticalTabChar`	`Integer`	character used as the 'vertical tab' character to go up one row
`backspaceChar`	`Integer`	character used as the 'backspace' character to go back one character
`tabChar`	`Integer`	character used as the 'tab' character to go forward one character
`log`	`Log`	a log for the screen

Screen Methods

The Screen object supports the following methods:

method name	description
`display`	display the supplied text on the screen at the current cursor position
`displayAt`	display the supplied text on the screen at the supplied cursor position
`extract`	extract text from the screen from the supplied position
`home`	'go home' i.e. move to the initial row and column without changing the screen content
`reset`	reset the screen i.e. move to the initial row and column and clear the screen
`up`	move the cursor position up one line
`down`	move the cursor position down one line
`left`	move the cursor position one character to the left
`right`	move the cursor position one character to the right
`cursor`	return the current cursor position
`isCursorOn`	test if the cursor display is turned on
`cursorOn`	turn the display of the cursor on
`cursorOff`	turn the display of the cursor off
`toHtml`	return an HTML representation of the screen content
`enableTrigger`	enable the identified trigger
`disableTrigger`	disable the identified trigger
`triggerDisplay`	display the supplied text and fire any appropriate enabled triggers
`viewer`	set up a COM object as a viewer to track the display of data on the screen
`string`	return a string representation of the screen
`fromString`	fill the screen from the supplied string representation
`find`	find the supplied piece of text on screen

`display`

Display the supplied text on the screen at the current cursor position.

Arguments:

data	`String` or `Binary`

Return type: the empty List ()

`displayAt`

Display the supplied text on the screen at the supplied cursor position -- the current cursor position is not affected.

Arguments:

data	`String` or `Binary`
row	`Integer`
column	`Integer`

Return type: the empty List ()

`extract`

Extract text from the screen from the supplied position.

Arguments:

row	`Integer`
column	`Integer`
length	`Integer`

Return type: String

`home`

'Go home' i.e. move to the initial row and column without changing the screen content.

Arguments: none

Return type: the empty List ()

`reset`

Reset the screen i.e. move to the initial row and column and clear the screen.

Arguments: none

Return type: the empty List ()

`up`

Move the cursor position up one line.

Arguments: none

Return type: the empty List ()

`down`

Move the cursor position down one line.

Arguments: none

Return type: the empty List ()

`left`

Move the cursor position one character to the left.

Arguments: none

Return type: the empty List ()

`right`

Move the cursor position one character to the right.

Arguments: none

Return type: the empty List ()

`cursor`

Return the current cursor position as a list of two integers (row column).

Arguments: none

Return type: List

`isCursorOn`

Test if the cursor display is turned on.

Arguments: none

Return type: the empty List () is returned if the cursor display is off, otherwise non-() is returned.

`cursorOn`

Turn the display of the cursor on.

Arguments: none

Return type: the empty List ()

`cursorOff`

Turn the display of the cursor off.

Arguments: none

Return type: the empty List ()

`toHtml`

Return an HTML representation of the screen content -- this forms the content of an HTML <table> statement.

Arguments: none

Return type: String

`enableTrigger`

Enable the identified trigger.

Arguments:

The initial argument is the trigger name -- any subsequent arguments are trigger-dependent. Any trigger can be re-enabled simply by supplying its name. Certain triggers require additional arguments when they are set up i.e. when they are initially enabled.

Enabling the following triggers requires no additional arguments:

home
reset
cursorOn
cursorOff

Setting up the hotText trigger requires the following arguments:

triggerName	`String` i.e. `"hotText"`
text	`String`
row	`Integer`
column	`Integer`

Setting up the hotPatch trigger requires the following arguments:

triggerName	`String` i.e. `"hotPatch"`
row	`Integer`
column	`Integer`
nRows	`Integer`
nColumns	`Integer`

Setting up the exitZone trigger requires the following arguments:

triggerName	`String` i.e. `"exitZone"`
row	`Integer`
column	`Integer`
nRows	`Integer`
nColumns	`Integer`

Setting up the messageRow trigger requires the following arguments:

triggerName	`String` i.e. `"messageRow"`
row	`Integer`

Return type: the empty List ()

`disableTrigger`

Disable the identified trigger.

Arguments:

triggerName String

Return type: the empty List ()

`triggerDisplay`

Display the supplied text and fire any appropriate enabled triggers.

Arguments:

text	`String` or `Binary`

Return type: a List of trigger names which have fired

`viewer`

Set up a COM object as a viewer to track the display of data on the screen.

Arguments:

viewer Dispatch

Return type: the empty List ()

`string`

Return a string representation of the screen.

Arguments: none

Return type: String

`fromString`

Fill the screen from the supplied string representation.

Arguments:

info String

Return type: the empty List ()

`find`

Find the supplied piece of text on screen -- the search starts checking at the supplied screen row and column. If supplied and non-(), the optional 4th argument makes the matching case-insensitive. The default is to do a case-sensitive search.

Arguments:

text	`String`
row	`Integer`
column	`Integer`
optional caseSensitivity	`Object`

Return type: List

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Current topic: communications

Related links: objects, built-in objects