HiDPI Screens – Ubuntu MATE vs. Xubuntu for HiDPI Screens

Your case studies are indeed challenging.

Take your Grandpa PC

Pentium 2 and 64Mb RAM.

Lubuntu minimum requirements are 128Mb if using the alternate installer - 256Mb for the Graphical installer.

The recommended RAM is 384Mb just to run the LiveCD.

Therefore - I'm afraid, you will not be able to install a graphical environment on Grandpa PC. At best you might get a text only "server" type install via a minimal ISO - i.e. you need a minimum of 64Mb to run the minimal CD.

The "old meat":

That is more promising:

Pentium 3 with 128Mb RAM - you should be able to squeeze on Lubuntu via its alternate CD.

However the minimum requirement for Xubuntu is 256Mb with 512Mb as a recommended RAM size.

I've experimented with various "low" RAM installs. I've never tried 128Mb - but in general, I install from a minimal ISO CD and install various components manually - for example, SLIM, LXDE with apt-get install --no-install-recommends to ensure no excess packages are installed.

Typical packages you should look out for if you go this route are described in the linked question below.

Stick with a lightweight browser such as midori - abiword should be ok for wordprocessing.

Flash and general movies will struggle with your video card. However playing music should be fine (see below)

Links:

1. https://help.ubuntu.com/community/Installation/MinimalCD
2. How do I install LXDE / Lubuntu?
3. Lightweight music player

No, there isn't any so far--see Answerer's note at the end.

What is "consistent"

Before one disagrees with this answer, make sure to understand the question by OP. Given that one needs to manually set DPI value or scale factor of desktop environment, which varies for different monitors, we can't say Ubuntu "handles HiDPI consistently".

I would understand "consistent" as more towards out-of-box experience (Even OP has mentioned this in the question). That is, in terms of the ability of operating system to use appropriate settings for any given hardware and application software that respects the settings.

Does Ubuntu offer out-of-box experience for HiDPI support? No, or mostly uncertain.

HiDPI support for Ubuntu

Trusty Tahr (14.04) is the first Ubuntu release that explicitly mentioned HiDPI support. Even before the release, relevant information can be traced back to this dated message.

cairo 1.13 snapshot in the ubuntu-desktop ppa (Hi-DPI support testing)

Better support for Hi-DPI screen is a topic that is being discussed for the coming LTS [...]

From TrustyTahr/ReleaseNotes for 14.04:

• Support for High-DPI screens and desktop scaling
• Initial HiDPI support for LibreOffice

From XenialXerus/ReleaseNotes for 16.04:

• Improved HiDPI support in the greeter
• Support for scaling cursors in HiDPI environments

HiDPI support for others

From blog post Kubuntu and HiDPI Screen dated 16 February 2016, by Giri Alam:

Kubuntu/KDE is not perfect on HiDPI screen. Currently, there is no utility to automatically detect and scale the UI based on device screen resolution and Dots Per Inch (DPI) value, but the workaround to make Kubuntu more usable on HiDPI screen is quite simple.

From blog post Ubuntu MATE 16.10 Alpha 1 dated late June 2016, on Ubuntu MATE blog:

We have initial HiDPI support (almost) working. Don’t get too excited, this is an all or nothing implementation. When enabled all GTK3+ applications (not just MATE) will be rendered using high quality pixel doubling. If you have a 2160p display, it looks ace :-D

However, no mention of HiDPI support status in the final release note of Ubuntu MATE 16.10.

From GNOME Wiki HowDoI/HiDpi:

GNOME currently enables hi-dpi support when the screen resolution is at least 192 dpi and the screen height (in device pixels) is at least 1200.

From reddit thread of BudgieRemix dated mid-June 2016, prior to becoming Ubuntu Budgie:

There doesn't seem to be HiDPI Support in any native settings menus, or on the lock screen. Scaling on the lock/login screen was added to Ubuntu 16.04 for HiDPI monitors. [...] scales everything correctly with a scale factor of 2, however there is one issue. [The icons in the system tray] do not scale and do not appear correctly.

And the only replied answer:

None of the current members of the development team has a HiDPI monitor so we cannot reproduce the issues you raise :(

Overall HiDPI support

Although I have not quoted other sources here, most mentioned flavours for HiDPI support are Ubuntu GNOME and Ubuntu (Unity). Some mentioned Kubuntu/KDE and Xubuntu/Xfce, but not much information for hardware that actually worked for these flavours.

Disclaimers: This answer intends to review HiDPI support status, as 2016, for Ubuntu and its official flavours. The following limitations shall be noted.

• Some flavours are not mentioned at all because those had no relevant information of HiDPI support

• Non-Ubuntu flavours or unofficial derivatives are not mentioned, such as Linux Mint/Cinnamon, elementary OS/Pantheon

• I don't have any HiDPI monitor or HiDPI supported hardware to verify above information; This answer solely quotes relevant information from the web

TL;DR The HiDPI support is work in progress, regardless of distribution and desktop environment. There isn't any Ubuntu flavour that handles HiDPI consistently yet.

Answerer's note: The HiDPI support may have improved since this answer was first written. Hence this answer is now a community wiki, so that anyone with minimum reputation can improve this post to keep up with how HiDPI support is being made consistent for newer releases of Ubuntu and the official flavours.