Hello Ed, hello all,

It is also the first time that I become active in this mailing list, although I'm already monitoring this list for half a year to get familiar with your conventions. I am co-founder of a software and consulting company in Germany. We develop a system (JACAMAR) that combines a serverless no-sql database engine with a customizable user interface for do-it-yourself non-IT expert end users. We started with an Eclipse based user interface, switched in 2015 to a self developed UI and unfortunately found out only very late that JavaFX did just the same with, I guess, a lot more resources than we have. So we switched another time to JavaFX and are about to launch our next version. By going this way, we have gained a lot of insights in the field of user interfaces.

To come to your question:
Yes we also experienced issues of poor performance on scrolling virtual tables with a lot of columns. The reason is in the nature of the VirtualFlow, which is the base of TableView: It has a "virtual" direction and a "static" direction. By default the vertical direction is the virtual one. That means the vertical scrollbar works with a value p between 0 and 1. Depending on how quick you scroll, only those lines are calculated and rendered, which will become visible in the the viewport for a given p. This gives good performance for tables with huge amount of lines. The problem is now the horizontal direction. Since this dimension is static, TableRowSkin calculates and renders all TableCells of each TableRow independent of its actual visibility in the view port. (see TableRowSkinBase line 519ff.) This works well for TableRows with relatively low number of columns. And knowing that, it is obvious, why the horizontal scrolling works so quick in your application, because all cells are already prepared and just need to be moved in X to become visible.
There are 2 opportunities how to attack that issue:
1.) If you don't have many lines, you could just change the vertical property to false (see VirtualFlow line 745). We did it only in a test case so far, so we don't have a lot of experience about that. 2.) is a tradeoff between vertical and horizontal performance. A code change would be required in TableRowSkinBase to restrict the actual creation of TableCells for one line to only those cells that will become visible for a particular scroll pulse. That way only 10-20 cells are affected for each line and not 300 any longer. If you now scroll horizontally, all new cells that become visible, must be additionally calculated and rendered at that point in time. Unless you have a 50-inch screen, there shouldn't be so many cells, so the loss of performance in horizontal direction should be manageable.

At the moment I am still very occupied with our system launch, but I intend to participate soon in the community and give back a little bit of what we received from using JavaFX for free in our applications up to now.

Greetings
Clemens


Am 25.01.2020 um 02:39 schrieb Ed Kennard:
Hi everyone,

I’m new to the list, so by way of a short introduction, I’ve been working with 
JavaFX for the last 4 years developing a commodities trading risk management 
system from the ground up for a software company I co-founded in London.  All 
our code is written in Scala, the functional style of which is essential for 
the mathematical heavy lifting needed on the backend, but which also lends 
itself really well to UI programming and working with JavaFX.  I’m enthusiastic 
about JavaFX and would love to make a contribution to the project.

At the center of our product is an extension of the TableView control that’s 
responsible for displaying all the output from our pivot reporting engine.  
Depending on how the user configures the layout of their pivot reports, 
sometimes there are a legitimately large number of columns (300+).  When that 
happens, while the horizontal scrolling remains perfectly smooth, the vertical 
scrolling degrades to a somewhat juddery state and CPU usage spikes.

I found an issue raised about this in 2019 on the old JFX GitHub repo here…
https://github.com/javafxports/openjdk-jfx/issues/409

…but I’m not sure whether, per Kevin’s suggestion at the bottom, it was ever 
submitted through the correct channels.  I can confirm that the test code 
included there by “yososs” on 20th May 2019 perfectly illustrates the problem 
I’m experiencing.  The same person seems to have a fairly clear theory on what 
is causing the problem, too - see their follow-up comment on 12 Sept 2019.

So, my questions to the list are:


   1.  Has anyone seen this issue raised anywhere else?
   2.  If yes, has anyone taken a look into it yet, and possibly even found a 
fix?
   3.  If no to both of the above, shall I submit it through the correct 
channels then have a crack at fixing myself?  Or is the issue likely to be a 
much deeper and far-reaching one than I’m anticipating?

Many thanks

Ed

--
Mit freundlichen Grüßen / Kind Regards

Clemens Kadura
Development Leader
Co-founder

*JACAMAR - agiles Datenmanagement im Team
Weitere Informationen auf www.jacamar.de <https://www.jacamar.de> *



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