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Sergio avatar Ubuntu

How can I revert from using GTK 3 to GTK 2 on Kunbuntu 20.04?

in flag
Sergio

I am using OpenCPN 5.2.4 with OpenGL (required for overlaying radar over charts) under Kubuntu 20.04. A tracked OpenCPN bug related to using GTK3 prevents OpenCPN from scaling the display appropriately when the display scaling is used (I use 200% to scale on a 15.6-inch 4k display).

A temporary workaround is to use GTK2 instead of GTK3.

My question is: How can I revert down to GTK2 on my system?

Any hints on how to proceed would greatly be appreciated.

System Info:

  • Operating System: Kubuntu 20.04
  • KDE Plasma Version: 5.18.5
  • KDE Frameworks Version: 5.68.0
  • Qt Version: 5.12.8
  • Kernel Version: 5.4.0-77-generic
  • OS Type: 64-bit
  • Processors: 4 × Intel® Core™ i5-4570T CPU @ 2.90GHz
  • OpenGL: 3.0 Mesa 20.2.6
$ apt-cache policy opencpn 
opencpn: 
Installed: 5.2.4.0-0~focal1 
Candidate: 5.2.4.0-0~focal1 
Version table:
 *** 5.2.4.0-0~focal1 500 
500 ppa.launchpad.net/opencpn/opencpn/ubuntu focal/main amd64 Packages 
100 /var/lib/dpkg/status 5.0.0+dfsg-1 500 
500 nz.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
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guiverc avatar
cn flag
guiverc
Download the source code, ensure all GTK3 calls are GTK2 compatible and adjust/recode those that use GTK3 features to limit themselves (& code functionality) to GTK2 compatible ones, then re-compile code. GTK3 & GTK2 APIs differ so you can't replace GTK3 with GTK2 packages... all programs need to be ported which is a load of work (why MATE took a long time to port, as did XFCE etc... let alone GNOME)
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guiverc avatar
cn flag
guiverc
Your alternative is creating a program like `wine` that catches all GTK3 calls, and tries to convert them to GTK2 calls & calls the GTK2 libs to do what GTK2 can do... What it does with the GTK2/GTK3 differences is the hard part; it can either ignore that (which will likely create segfaults or have an *unreliable* or *unstable* effect on the calling program, OpenCPN in your case) and won't be very reliable with a load of constant & future tweaking as GTK3 changes occur into the future...
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N0rbert avatar
zw flag
N0rbert
Why do you really think that issues are caused by GTK2? You are probably using non-standard version of OpenCPN, the default repository provides [5.0.0 version](https://packages.ubuntu.com/focal/opencpn). Did you have problems with OpenCPN while using older versions [from 2019](https://changelogs.ubuntu.com/changelogs/pool/universe/o/opencpn/opencpn_5.0.0+dfsg-1/changelog) which are probably GTK2 based? Which installation source do you use for OpenCPN? What is the output of `apt-cache policy opencpn` ?
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Sergio avatar
in flag
Sergio
The issue is with GTK3 (https://github.com/OpenCPN/OpenCPN/issues/1927#issuecomment-868587708). OpenCPN, the default repository provides 5.2.4. apt-cache policy opencpn opencpn: Installed: 5.2.4.0-0~focal1 Candidate: 5.2.4.0-0~focal1 Version table: *** 5.2.4.0-0~focal1 500 500 http://ppa.launchpad.net/opencpn/opencpn/ubuntu focal/main amd64 Packages 100 /var/lib/dpkg/status 5.0.0+dfsg-1 500 500 http://nz.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
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Score:1
guiverc avatar Ubuntu
cn flag
guiverc
  • download the source code [to OpenCPN 5.2.4]
  • ensure all GTK3 calls are GTK2 compatible
  • adjust/recode those that use GTK3 features so they are limited to GTK2 functionality and make GTK2 calls
  • re-compile code.

GTK3 & GTK2 APIs differ so you can't replace GTK3 with GTK2 packages (what I suspect you were hoping).

Programs need to be ported which is a load of work (why MATE took a long time to port, as did XFCE etc... let alone GNOME when it ported from GTK2 to GTK3, and now currently in the move to GTK4)

If it wasn't clear - the work that needs to be done is done in the OpenCPN program and OpenGL; ie. the end-user programs that currently call GTK3 - those need the change.

A system can have GTK3 & GTK2 co-existing; eg. my Lubuntu impish system has both Qt5, GTK3 & GTK2 libs installed and they'll happily co-exist.

  • hexchat (my chosen IRC client) calls GTK2 libs
  • liferea & evolution (my chosen RSS & MUA) call GTK3 libs
  • my Lubuntu LXQt desktop, it's programs eg. featherpad call Qt5 libraries, just like your KDE desktop will (many KDE apps also need KF5).

It's the end-user program that needs to be changed. You can install all the GTK2 toolkit/library in your system, but if nothing calls it, it won't be used.

Also note: Scaling doesn't exist in GTK2 so I don't see what you hope to achieve.

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guiverc avatar
cn flag
guiverc
FYI: Why my chosen apps... I used to be a GNOME user long ago (GTK2) days, and some end-user apps I've just not kicked...
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Sergio avatar
in flag
Sergio
Ok that clarifies a lot of things for me. Looks like I am gonna have to wait for the OpenCPN developers to fix this on a future release. It's way above my competencies to 'recode' and 'recompile' as suggested. p.s.: Meanwhile, I am stuck with a system migration and display update that OpenCPN can't handle (Window to Kunbutu with a 15.6inch 4k display that needs the scale set at 200% in order to be usable).
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