bug#51343: 27.2; Xaw3d scrollbar thumb doesn't update while dragged

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Po Lu [2021-10-23 15:32:48] wrote:
> Previously, in an Emacs built with Xaw3d scroll bars, the thumb
> proportion would update as the scrollbar was dragged.  Now it doesn't
> update until the scrollbar is released, and something that makes the
> scrollbar position change happens.

To give you some context:

Many years ago, I spent a fair bit of time trying to get scrollbars
working "right".  It's a major pain in the ass, because most toolkits
don't support our requirements: once the bottom of the thumb hits the
bottom of its course it stops there, but the corresponding top part of
the thumb may correspond to a window-start which leads to a screen where
point-max is not visible (in response to which we'd reduce the size of
the thumb, but that happens too late (either because the toolkit has
already decided not to tell us that the user's mouse was trying to go
further, or because the toolkit doesn't support updating the thumb size
while dragging it).

There was a simple patch to Xaw3d which made it behave more like Xaw (by
making the Xaw3d more like Xaw's) and made the whole thing work
perfectly for us, but it was never accepted upstream because it went
against their philosophy of what "the metaphor should be".


        Stefan