Smooth scrolling

Craig newman craig at
Tue Feb 2 09:16:24 EST 2021

On a Mac, I made a field with 25000 words or so. Certainly dragging the
thumb is jerky.

But dragging the thumb forces the field's scroll  to track the thumbPos, as
it relates to the number of lines and the total "pixel" travel available to
that thumb. I don't see how a field could scroll smoothly at all, since the
thumb and the scroll are locked together.

In other words, how can it "glide" from one line (scroll position) to
another, since the thumbPos has a finite number of possible locations, and
if there are a LOT of lines, each location may be several lines away?


-----Original Message-----
From: use-livecode [mailto:use-livecode-bounces at] On Behalf
Of Richard Gaskin via use-livecode
Sent: Monday, February 01, 2021 10:11 PM
To: use-livecode at
Cc: Richard Gaskin <ambassador at>
Subject: Re: Smooth scrolling

David Epstein wrote:

 > My impression is that a LiveCode field scrolls less smoothly than  > a
comparable field in some other programs, such as MS Word and  > Scrivener.
If I paste about 25,000 words into a word wrapped  > scrolling field, and
then drag the scrolling thumb up and down  > there is much more jumpiness
than I see when I do the same thing  > to the same text in those other
programs.  (LC 9.6 on Mac OS 10.12.6).
 >  Do others see the same thing?  Does anyone know the underlying cause  >
of this, or a remedy?

Nice to hear the name Scrivener. Blount did some good rethinking of how
words are managed when he came up with that app.

In the olden days I remember being impressed with how smoothly LC scrolled
vs things like Word, which wasn't all that surprising given that LC buffers
the whole field in RAM while Word pages from disk.

A lot's changed since then. Not only have SSDs taken over to narrow the gap,
but I no longer have a copy of Word to compare anything to. :)

But I did just do a quick test of LC v9.6.2rc2 vs LibreOffice Write on
Ubuntu 18.04, using Kafka's Metamorphosis to get a reasonably close number
of words to your test (Gutenberg Project RTF is 25,180 words: ).

Very different setup of course, but FWIW LC and LibreOffice are quite close
in scrolling, though LC seems noticeably smoother.

Of course Ubuntu and macOS couldn't be more different from top to bottom,
with different font managers, buffering APIs, compositors, etc., so while it
was easy for me to do this quick test it's almost entirely useless.

What might be nice would be someone with good knowledge of Apple low-level
tools, similar to the ones we see for Android or to some degree strace,
where graphical UI stuff can be profiled so we can see what Word and LC are
doing differently.

It might also be worth setting the field's layerMode to "scrolling" and the
stack's compositorType to "CoreGraphics" to see if that improves things.

  Richard Gaskin
  Fourth World Systems
  Software Design and Development for the Desktop, Mobile, and the Web
  Ambassador at      

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