A `PangoGlyphItem` is a pair of a `PangoItem` and the glyphs resulting from shaping the items text.

As an example of the usage of `PangoGlyphItem`, the results of shaping text with `PangoLayout` is a list of `PangoLayoutLine`, each of which contains a list of `PangoGlyphItem`.

Modifies @orig to cover only the text after @split_index, and returns a new item that covers the text before @split_index that used to be in @orig.

You can think of @split_index as the length of the returned item. @split_index may not be 0, and it may not be greater than or equal to the length of @orig (that is, there must be at least one byte assigned to each item, you can't create a zero-length item).

This function is similar in function to pango_item_split() (and uses it internally.)

Splits a shaped item (`PangoGlyphItem`) into multiple items based on an attribute list.

The idea is that if you have attributes that don't affect shaping, such as color or underline, to avoid affecting shaping, you filter them out (method@Pango.AttrList.filter), apply the shaping process and then reapply them to the result using this function.

All attributes that start or end inside a cluster are applied to that cluster; for instance, if half of a cluster is underlined and the other-half strikethrough, then the cluster will end up with both underline and strikethrough attributes. In these cases, it may happen that @item->extra_attrs for some of the result items can have multiple attributes of the same type.

This function takes ownership of @glyph_item; it will be reused as one of the elements in the list.