start index
end index (the range is the set of bytes with indices such that start <= index < end)
rectangle used to store the extents of the glyph string range as drawn or NULL to indicate that the result is not needed.
rectangle used to store the logical extents of the glyph string range or NULL to indicate that the result is not needed.
Computes the extents of a sub-portion of a glyph string. The extents are relative to the start of the glyph string range (the origin of their coordinate system is at the start of the range, not at the start of the entire glyph string).