Converts from x offset to the byte index of the corresponding character within the text of the layout.
x_pos is outside the line,
trailing will point to the very first or very last position in
the line. This determination is based on the resolved direction of the paragraph; for example, if the resolved direction is right-to-left, then
an X position to the right of the line (after it) results in 0 being stored in
trailing. An X position to
the left of the line results in
index_ pointing to the (logical) last grapheme in the line and
trailing being set to
the number of characters in that grapheme. The reverse is true for a left-to-right line.
the X offset (in Pango units) from the left edge of the line.
location to store calculated byte index for the grapheme in which the user clicked
location to store an 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.