kritarth authored Dec 12, 2016 and Sébastien Lafargue committed Dec 12, 2016

Currently, the build log panel is bound to scroll to end whenever new output
is added to the buffer using gtk_text_view_scroll_to_mark. In order to disable
this auto-scrolling I added horizontal and vertical GtkAdjustments. These
adjustments are initialised in gbp_build_log_panel_init(). They point to
the adjustments of GtkScrolledWindow scroller. With these adjustments I check
if the user has scrolled back or right manually.

expression1: value >= upper - page_size - offset
This expression returns true if the user has not scrolled vertically back.
The 'offset' is defined as VERTICAL_AUTOSCROLL_TOLERENCE - this means the
limit upto which scroll-on-output will still work even if the user has
manually scrolled.

Similarly HORIZONTAL_AUTOSCROLL_TOLERENCE is defined.
Detection of horizontal scrolling is done by
expression2: value <= HORIZONTAL_AUTOSCROLL_TOLERENCE
HORIZONTAL_AUTOSCROLL_TOLERENCE is set to 3 because the left-margin of text_view is also set at 3.

if (expression1 && expression2) then
        set the vertical adjustment to upper - page_size
        apply this adjustment to the container

https://bugzilla.gnome.org/show_bug.cgi?id=775642