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Chapter 7 - Text Services Manager / Text Services Manager Reference

Apple Event Handlers Supplied by Client Applications

Converting Global Coordinates to Text Offsets

The Position To Offset Apple event requests a client application to convert specified global coordinates to byte offsets in text. The text service component uses this Apple event for mouse tracking, in order to draw the caret, highlight text, or adjust the cursor appearance.

Position To Offset--Converting Global Coordinates to Text Offset (Continued)
Event class	kTextServiceClass
Event ID	kPos2Offset
Requested action	Convert global coordinates specified in the keyAECurrentPoint parameter to a byte offset. If the click is within the limits of the active input area, the offset is relative to the start of the active input area. Otherwise, the offset is relative to the start of the application's body text. The client application specifies the classification of the location of the offset in the keyAERegionClass return parameter.
Required parameters
Keyword:	keyAETSMDocumentRefcon
Descriptor type:	typeLongInteger
Data:	A TSM document specifier (reference constant) supplied by the application in a prior call to the NewTSMDocument function (see page 7-50). This value is associated with the TSM document affected by this event.
Required parameters
Keyword:	keyAEServerInstance
Descriptor type:	typeComponentInstance
Data:	A component instance value created by a prior call to the Component Manager OpenComponent function. This value identifies the text service component.
Keyword:	keyAECurrentPoint
Descriptor type:	typePoint
Data:	A point that contains the global coordinates that describe the current mouse position.
Optional parameter
Keyword:	keyAEdragging
Descriptor type:	typeBoolean
Data:	A Boolean value that indicates whether the input method is currently tracking the mouse--that is, whether the user is dragging the current selection. If it is TRUE, the application should pin the cursor to the limits of the active input area (to avoid highlighting beyond the limits of the active input area).
Return parameters
Keyword:	keyAEOffset
Descriptor type:	typeLongInteger
Data:	A byte offset that specifies the character corresponding to the current mouse position (keyAECurrentPoint). If the click is within the limits of the active input area, the offset is relative to the start of the active input area. Otherwise, the offset is relative to the start of the application's body text.
Keyword:	keyAERegionClass
Descriptor type:	typeShortInteger
Data:	The classification of the position specified in the keyAEOffset parameter. Three constants define the classification:
	Constant	Value
	kTSMOutsideOfBody	1
	kTSMInsideOfBody	2
	kTSMInsideOfActiveInputArea	3
	A value of kTSMOutsideOfBody means that the offset is outside the application's body text. A value of kTSMInsideOfBody means that the offset is inside the body text. kTSMInsideOfActiveInputArea means that the offset is inside the active input area.
Return parameters
Keyword:	keyErrorNumber
Descriptor type:	typeShortInteger
Data:	Any errors that the application needs to return to the text service component. The application must pass Memory Manager, TextEdit, or other errors that it receives through to the component; otherwise, it should pass 0 (noErr).
Optional return parameter
Keyword:	keyAELeadingEdge
Descriptor type:	typeBoolean
Data:	A Boolean value that is equivalent to the leadingEdge parameter of the QuickDraw PixelToChar function. It is TRUE if the specified point corresponds to the leading edge of the character whose offset is returned; it is FALSE if the specified point corresponds to the trailing edge of the character.

For sample code that handles the Position To Offset Apple event, see Listing 7-8 on page 7-30.