Converts from X and Y position within a layout to the byte index to the character at that logical position. If the Y position is not inside the layout, the closest position is chosen (the position will be clamped inside the layout). If the X position is not within the layout, then the start or the end of the line is chosen as described for Layout.lineXToIndex. If either the X or Y positions were not inside the layout, then the function returns FALSE; on an exact hit, it returns TRUE.
the X offset (in Pango units) from the left edge of the layout.
the Y offset (in Pango units) from the top edge of the layout
location to store calculated byte index
location to store a integer indicating where in the grapheme the user clicked. It will either be zero, or the number of characters in the grapheme. 0 represents the leading edge of the grapheme.
TRUE if the coordinates were inside text, FALSE otherwise.