Gtk.TextView.prototype.scroll_to_iter

function scroll_to_iter(iter:Gtk.TextIter, within_margin:Number, use_align:Boolean, xalign:Number, yalign:Number):Boolean {
    // Gjs wrapper for gtk_text_view_scroll_to_iter()
}

Scrolls text_view so that iter is on the screen in the position indicated by xalign and yalign. An alignment of 0.0 indicates left or top, 1.0 indicates right or bottom, 0.5 means center. If use_align is false, the text scrolls the minimal distance to get the mark onscreen, possibly not scrolling at all. The effective screen for purposes of this function is reduced by a margin of size within_margin.

Note that this function uses the currently-computed height of the lines in the text buffer. Line heights are computed in an idle handler; so this function may not have the desired effect if it's called before the height computations. To avoid oddness, consider using Gtk.scroll_to_mark which saves a point to be scrolled to after line validation.