Highlighting

TextEdit highlights a group of characters that is contiguous in memory

(backing-store order). However, the highlighted text may appear

discontinuous on the display line if the selection contains mixed- directional

text, as shown in the next figure. This is because TextEdit draws characters

in display order, which may be different from backing-store order. The caret

positions are also determined similarly. The display order is determined by the

ordering of the characters within a direction run and the ordering of direction

runs in the primary line direction.

Character offsets are byte offsets of the characters in the text buffer, and the

values of character offsets correspond to the backing-store order of

characters.

Discontinuous highlighting display

A caret position is a location on the screen corresponding to a leading or

trailing edge of a displayed character. In mixed- directional text, one character

offset may correspond to two caret positions, and one caret position may

correspond to two character offsets.

These ambiguous cases occur at direction boundaries because the character

offset is associated with two different characters-the one before and the one

after the offset. When these characters are not adjacent in the display, two

caret positions result. The primary caret position is the screen location

associated with the character that has the same direction as the primary line

direction. The secondary caret position is the screen location associated with

the character that has a different direction from the primary line direction.

TextEdit uses only the primary caret positions in determining which

characters are highlighted.

In the previous figure and in the next figure, you can see how the primary and

secondary caret positions differ at direction boundaries 4 and 12. In the next

figure, you can see the relationship between the character offsets and the

primary and secondary caret positions. The next figure illustrates how

TextEdit uses primary caret positions to define highlighting boundaries for

the highlighting of characters 2, 3, 4, and 5. The shaded regions indicate the

highlighted characters. To highlight characters 2 and 3, TextEdit inverts the

entire area between primary caret positions 2 and 4. To highlight characters 4

and 5, it inverts the entire area between primary caret positions 12 and 6.

Highlighting mixed- directional text.

When a non-Roman script system is installed, TextEdit calls the

(with a direction value of smHilite) to ascertain which characters should be

highlighted.

TextEdit routines that specifically need highlighting of a selection or that

produce highlighting as a result of their functions include TEActivate,

Referenced by (7):