Question: I am running Gnome Shell with a 4k monitor and there are a few applications that I use that don't scale at all with the high resolution.

Here is an example of LMMS, an application that hasn't yet been ported Qt 5, so it doesn't have high dpi scaling capabilities:

[![Screenshot](https://i.stack.imgur.com/Af0Vr.jpg)](https://i.stack.imgur.com/Af0Vr.jpg)  

(Click images to enlarge)

Is there any way to scale a specific X window without changing the display resolution?

My current solution is to half the dimensions of my display resolution, but this degrades the resolution of every other application that supports proper dpi scaling:

[![Screenshot](https://i.stack.imgur.com/fJVFL.jpg)](https://i.stack.imgur.com/fJVFL.jpg)

Answer: 
I finally managed to find a solution that scales old applications without any noticeable visual or performance degradation.

Thanks to kaueraal, you can now scale old applications using `run_scaled`. You can obtain the script from either his [GitHub page](https://github.com/kaueraal/run_scaled) or as part of the `xpra` package if you are running Arch Linux.

Here is an example of two applications running side by side:

* Firefox with HiDPI support on the left
* LMMS running with `run_scaled` on the right

[![enter image description here](https://i.stack.imgur.com/VwIjQ.jpg)](https://i.stack.imgur.com/VwIjQ.jpg)

I discovered this script through the [Arch Linux Wiki](https://wiki.archlinux.org/index.php?title=HiDPI&oldid=468803#Unsupported_applications).
Without seeing the exact problem that you are running into I would suggest using 

```
GDK_SCALE=x

```

or

```
GDK_DPI_SCALE=x

```

Before starting each application. You will likely have to manually change `.desktop` files or run from your shell prefixing the commands with `GDK_SCALE=x`

`GDK_SCALE` only allow interger values however
`GDK_DPI_SCALE=x` allow for decimal values like i.e.`GDK_DPI_SCALE=0.66`

For other SDK based applications there are likely similar settings for respective kits. However since your problem is with gnome desktop I will provide this solution.

I haven't tried with a 4k monitor, but running `GDK_DPI_SCALE=1.66 gnome-calculator` will demo the solution.

Source: <https://developer.gnome.org/gtk3/stable/gtk-x11.html>