Lays out formatted text for display.

The class provides functions to:

convert between document positions and x,y coordinates

set the dimensions of the rectangle in which text can be viewed (the view rectangle)

set margin widths

do horizontal and vertical scrolling

do text selection

set the cursor position and appearance

After a change has been made to the text layout, a reformat and redraw should normally take place. CTextView provides functions which are optimised to reformat the minimum amount necessary. For example, when a global formatting parameter is changed (e.g. the wrap width), the whole document's layout needs to be recalculated, so HandleGlobalChangeL() should be called. If the change involves the insertion or deletion of a single character, only a single line may be affected; for this, HandleCharEditL() is appropriate. Most CTextView reformatting functions do scrolling (using block transfer), if necessary, and a redraw.

For maximum responsiveness, CTextView uses an active object to carry out reformatting as a background task, so that the application can continue to receive user input. Many CTextView functions force background formatting to complete before they take effect.

When scrolling vertically, positive numbers of pixels, lines, paragraphs, pages, etc., mean that the text moves down, and vice versa. When scrolling horizontally, positive numbers of pixels mean that the text moves left and vice versa.

A text view can display up to two cursors and up to three margins. The cursors are the text cursor and the line cursor. The purpose of the line cursor is to make it easier to see which line the text cursor (or the selection extension point) is on. The three margins are the label margin (for paragraph labels), the line cursor margin (for the line cursor) and the left text margin (the gap between the edge of the page and the text). All are optional, but if present, they appear in that order, starting at the left edge of the view rectangle.

An object of class CTextLayout is used by the text view to calculate changes to the layout. This object must be specified when constructing the text view. It is also used to set layout attributes, including the wrap width, the height of the visible portion of the document (the "band"), whether formatting is set to the band or to the whole document and the text object which is the source of the text and formatting information.

The x-y pixel coordinates used by CTextView are called window coordinates. Window coordinates have their origin at the top left corner of the view window (unlike class CTextLayout whose coordinates have their origin at the top left corner of the area within the view rectangle in which text can appear). As in most bitmap graphics systems, x coordinates increase rightwards and y coordinates increase downwards.