Practically I felt bored one day and since I had just installed a new applet that does what the built-in commands should do but don't some ideas popped to mind. Someone on its specific page was asking ironically what this does that an older similar one doesn't. Well, for starters it doesn't ask the user to install an extra mandatory library. I like that.
Before continuing someone might ask why not go to github and interact directly with the developer/maintainer. Hell no. That place - besides belonging to Microsoft - is so weirdly structured that I just can't understand it. And even if I took one week or one month to try and grasp its concepts I'd forget everything within a couple days due to my bad memory. Not to mention the whole login procedure, which is unacceptable in either variant. So no github. If the current maintainer @cardsurf happens to be passing by I'll gladly have a chat.
OK, so the applet is called Brightness and Gamma Applet. Its official Spices page is here.
What have I done? First of all added a tooltip. I hate it when a tray icon doesn't tell me what it's doing there, more so when its icon is ugly-symbolic and ambiguous. So now it displays a nice tooltip with details on the screen and displays it's enabled for, the Mode (talk about that right away), and the percentual levels for Brightness and RGB. Tooltip gets updated in real time when scrolling mouse wheel over icon to adjust brightness.
Then I added a Mode switch upon middle-click that cycles through three different modes: Day, Night and Custom. For now only Brightness can be set to different values for each mode. It's more like a proof of concept, a test. If/when I feel again like messing with code I may improve it even further. Oh and there's also a brief popup notification when cycling through modes so the user knows exactly what was chosen since the tray icon does not (yet?) reflect current mode.
There are many other things to do, like saving/loading all custom values for all modes; for now they are hardcoded (for brightness only). Or options to choose specific icons for the popup notifications (and tray icon maybe, at some point). Other ideas would be welcome.
This mod has only been tested in Mint Cinnamon 19.2. Hopefully it works in other older or newer versions but that's for you to test and report back, if you want to.
Installation is as simple as unpacking the contents of the archive (folder included) in
~/.local/share/cinnamon/applets
.If already installed choose to overwrite all files. Of course, backup the existing applet's folder before overwriting, just in case.
a) If applet is already enabled and running, open Looking Glass (right-click panel > Troubleshoot > Looking Glass), select the Extensions tab,
find Brightness and gamma applet in the list, right-click it and choose Reload Code.
If it doesn't show back up in the tray switch to the Log tab and look at the bottom for any related error messages. Then please copy/paste here hoping it can be fixed. But hopefully there won't be any errors.
b) If applet was not previously installed you will have to open the Applets GUI (Main Menu > Preferences > Applets) and enable it there.
At the same place it can later on be disabled or uninstalled if so desired.
LATER EDIT:
Please read through the rest of the topic,there is now a fork of this B&G mod called Applet PYE sporting more features.
A download link for the latest version is placed here for convenience but it is advisable for you to read through as there may be useful hints and advices posted along. Most important advice is to first disable or uninstall all similar applets (B&G, B&G mod, Redshift, qRedshift etc) before installing and enabling Applet PYE - otherwise there will be conflicts that could even hang or crash Cinnamon.
MUCH LATER EDIT:
Yesterday (April 16, 2022) I noticed the applet wouldn't connect to the sunrise-sunset.org site anymore to retrieve the sunrise/sunset data. The log revealed the site SSL certificate had expired. Personally I'm not at all a fan of all this apparent security that only places obstacles in the way of ordinary people while the real bad ones fly over them with grace.
Therefore since waiting for a certificate renewal - if ever - was not an option I decided to go for a workaround and only today finally found it.
So if you have a problem with accepting expired certificates (for retrieving a few dozen words, really?) then by all means uninstall the applet or at least use it offline with manual settings (thankfully I had implemented that). Otherwise get the latest fixed version below.
Since the board attachment limit is too low I'll just post the latest version; previous versions can be found on my blog: Applet PYE is now at GitHub if anybody cares.
Here you are Brightness & Gamma Applet v1.1.2.1 based on official v1.1.2:
(latest version of the mod, v1.1.3.1, can be found a few comments below) Enjoy!