There have been a LOT of users here and on Facebook asking about this issue.
It's worth pointing out that this is not a Reaper specific issue. If you own any other DAW's and run them in HiDPI mode then you will see the same issues with the same third party plugins not scaling correctly. It is down to the plugin developers to code their plugins to support HiDPI scaling smoothly.
Reaper 6.0 supports HiDPI monitoring, and this is enabled by default. 5.0 does not, so
if your plugin GUI's are looking too small, or the theme you were using in 5.0 looks wrong, and you just want it to look like it did before you upgraded, here is what you do -
Preferences/General/Advanced UI/system tweaks.../HiDPI mode (I think this is called something different for mac users, but it's in the same place). In here you can switch Reapers HiDPI mode to 'unaware'. This will disable HiDPI, and make your plugins and themes look like they did in 5.0.
If you want to run Reaper in HiDPI, but just fix the small plugin GUI's, here are your options -
The new per-plugin HiDPI compatibility option introduced in 6.02. You can find it under the + menu or in the right click menu in the FX browser -
Pros - Plugin is scaled up to the correct, expected size when floating.
Cons - Does not work when viewing plugin in the FX chain. Causes weird GUI isses with some plugins. The N.I plugins being an example of this (I have just figured out a solution for this though, see below).
Run the plugin as a separate/dedicated process -
Pros - It will look 100% as it does when running in standalone, with no scaling or graphical issues.
Cons - Does not work with VST3 plugins (although there are always VST2 installer options for any VST3 plugins in my experience).
It will steal keyboard focus, so your keyboard shortcuts for play/record/stop etc will not be passed through to Reaper until you focus the Reaper window... a deal breaker for me personally. However, Edgemeal has just developed a simple (but genius) app that will pass certain key actions through from the bridged plugin window to Reaper... https://forum.cockos.com/showthread.php?t=219817 (check towards the end of the thread) If you use it, please donate to him.
OR - the new option I've just discovered. Run the plugin in a separate/dedicated process, but check 'embed bridged UI' AND the HiDPI compatibility switch on the plugin. This seems to fix the issue for 90% of the problem plugins (like the N.I ones). Once these options are checked they seem to work perfectly, no graphical glitches, and still respond to keyboard shortcuts.
So... with the combination of the solutions above, I am now running in HiDPI (4k) with basically all of my (too many) plugins running smoothly, scaling correctly and with no graphical glitches. In fact, now that I've got all this figured out, I'd say Reaper has some of the the best HiDPI plugin handling options of any DAW I've tried so far. Well done Devs (although the solutions to these issues could have been a bit more forthcoming, I understand you can't sit around testing every third party plugin that we're all using!).
I only wish that the HiDPI compatibility options also worked when plugins are displayed inside the FX chain, that's the last piece of puzzle here for me.
Hopefully this has been helpful.
Plugin GUI's too small since upgrading to 6.0? Here is the solution -
Linear Mode
