To allow you to compute selections on discontiguous text ranges, the functions described in this section return TTextRegion instances. Often these functions simply return a TTextRegion that contains a single TTextRange. However, if the range contains bidirectional text boundaries, the functions return a TTextRegion with multiple TTextRange instances. These appear as a single highlighted area. This mechanism for identifying bidirectional text boundaries prevents the behavior in some systems in which a single text range is computed and characters are highlighted with multiple highlight boxes.
The functions for computing discontiguous ranges are:
- GetTextRangeFromInsertionPoints computes the ranges that fall between two insertion offsets.
- GetTextRangeForLine computes the ranges that comprise the line.
- GetTextRangeUntilLineEnd and GetTextRangeUntilLineStart compute the ranges between a given insertion offset and either the start or end of the line.
- GetHighlightArea and AddToHighlightArea compute the highlight areas, as described in "Highlighting selected text ranges" on page 157, returning a TTextRegion.
- GetRightInsertionPoint and GetLeftInsertionPoint calculate the adjacent insertion offset from a discontiguous text selection (a TTextRegion).
TTextLineLayout also provides a function that allows you to extend ranges in a discontiguous selection. GetNearestEdge takes the currently selected region and a mouse position, and returns the insertion offset in the range closest to the position. This offset identifies the insertion point that should be extended when extending a text range.
To implement extendable selections:
- Call GetNearestEdge to retrieve the correct TInsertionOffset.
- Create a new TTextRegion from this TInsertionOffset and the final mouse position.
- Union the new range with the original range to compute the final selection region.
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