1.167 class text_image

Class text_image takes care of mapping a one-dimensional array of (character,font,colour,attribute) quadruples onto a two-dimensional text image as we normally like to see text displayed. This class is used both by class editor and class list_browser to manage the text-part.

Class text_image uses dedicated interface techniques to their associated editor or list_browser and cannot be used outside this context. This prohibits the use of text_image objects outside the context of editor or list_browser by the application programmer.

Most behaviour of class text_image is just for communication with the associated editor or list_browser. Of interesting to the user may be:

text_image<->tab_distance	Distance between (regular) tab-stops
text_image<->tab_stops	Vector of tab-stops
text_image<->wrap	How long lines are handled

Bugs: We should realise boxed text-style and horizontal scrolling.

See also

- editor-image
- class font

1.167.1 Instance variables

text_image-change_start: alien:int

Start of changes (character index).

text_image-inserted: alien:int

How much text was inserted/deleted.

text_image-change_end: alien:int

These variables are used by text_image->compute to determine the range of the text that should be updated and the area of the text_image<-image that is to be repainted.

text_image-scan: alien:ScanFunction

C-Function to scan for a syntactical category.

text_image-seek: alien:SeekFunction

C-Function to seek to a position.

text_image-fetch: alien:FetchFunction

C-function pointers obtained from the text_image<-text to perform the following low-level action:

-fetch	Read next character with attributes
-seek	Set index for next -fetch operation
-scan	Scan for a syntactical category

text_image-map: alien:TextScreen

Array of line descriptions. Each line describes a screen-line: character index for the start, displayed characters, fonts, colours and attributes. This map is updated by text_image->compute. See also text_image->dump_map.

text_image-start: int

Start is normally the start of a line of the underlying text (e.i. the first character after a newline character). It will be made the text_image<-start of the text_image. SkipLines is the number of screen lines to omit and may be used to start the screen in the middle of a wrapped long line. The default skip_lines is 0.

text_image<-start returns the character index for the first character of the nth (1-based) screenline. By default this is the first visible character.

text_image <- tab_stops: vector*

Vector of tab-stops in pixels. When defined, this overrules text_image<->tab_distance.

text_image <- text: object

Holder of the text. The text should implement:

text_image<-_seek_function	get -seek function
text_image<-_scan_function	get -scan function
text_image<-_fetch_function	get -fetch function

Besides this, it should notify changes to the text_image object using:

text_image->_changed_region	Indicate text in region has changed
text_image->_insert	Indicate insert/delete

This functionality is currently reserved for the C-programmer.

1.167.2 Send methods

text_image ->center: index=int, line=[int]

Scroll the text such that the character at the given index is on the given physical line (1-based) of the window. When line is omitted, index will be placed around the center of the image.

text_image ->compute:

Updates the -map and informs the redrawing system of the part of the image that needs to be updated.

text_image ->dump_map:

Dump map of the screen. Used for system maintenance only. See also -map and text_image->compute.

text_image ->wrap: {none,character,word}

Wrap mode for long lines. This has several implications on the behaviour of editor. Please check editor->wrap for details.

1.167.3 Get methods

text_image <-character_position: int -> point

X-offset, Y-BaseLine of character at the given index.

text_image <-index: event -> int

Translate an event into the index of a character. This method is used by class editor and class list_browser to implement pointer-associated event-handling. It may be used when connecting specialised event-handling to an editor or list-browser.