character-index-at-position

Arguments: text-edit-pane position

Returns the zero-based index of the character at position in text-edit-pane if that pixel position is currently scrolled into view, and otherwise returns nil. If there is no character at the specified position (but that position is scrolled into view), then the index of the nearest character is returned.

text-edit-pane should be a text-edit-pane or rich-edit-pane.

position should be a position object (see make-position) in stream coordinates, meaning that it is measured from the upper-left corner of the scrollable contents of the window, and so the value is not affected by the current scroll-position of the window.

(The functionality that is exported by the Windows rich-edit control, which we use for all text-edit-panes in Windows, does not appear to provide a way to determine the character when it is not scrolled into view. There is also no way to programmatically scroll this control to an arbitrary pixel position (in version 1.0), though set-first-visible-line will scroll a particular line of text to the top.)

See also position-of-character-index.

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Created 2010.1.21.