One of the nicer looking visualizers I have seen yet...
While dgrace should certainly be fully credited for AudioLevel, I am only a minor player in the development of Rainmeter. Quite a few folks have had important roles, both past and present. I accept the thanks on behalf of the Rainmeter Team, and say you're welcome!.
I don't know, I suppose there are lots of ways you could come at that. I'd at least be tempted to use AudioLevel to get the "low end" of the signal, the "beat" if you will. Then use that value to drive ColorMatrix on the background image to lighten or darken the green based on it.
I'm certainly no expert on the AudioLevel plugin, so I'm not sure how best to get it to measure the "beat" in a song, but assuming that can be done, (and I'm pretty sure it can, based on the "throbbing" subwoofer skins I have seen around) then there are a lot of ways to react and change the image. ColorMatrix, ImageTint, ImageAlpha, etc.
Yeah, using RGB colors and ImageTint is one approach. I'd really be tempted to at least explore ColorMatrix for this though, as it gives you much finer control over things. Rather than "tinting" the entire image some color, you can specifically target just the "green" values, and do some very cool stuff with them. Add more or less green, adjust the luminescence, ect. It can get just a tad complicated, but worth wrapping your head around, not only for this, but in general.
I quick-and-dirty separated the "border" from the "center", as that just seemed nicer for my tastes. Seems to me to be a better illusion of a "window". I just tint the center.
BackBorder.png
BackCenter.png
test.gif
If you replace the random number Calc with an AudioLevel child measure, which measures from 0 to 1, you are off and running.
While this simple use of ColorMatrix just more or less duplicates the functionality of ImageTint, it does have the advantage of not requiring a few extra measures to deal with the red, green, blue as separate things.
You do not have the required permissions to view the files attached to this post.
Always a few different ways to do things in Rainmeter...
I don't know what issue you have with my code, you must have some typo somewhere. It's not really about tinting from out -> in or in -> out, it just adds color to every pixel in the image, while keeping the existing transparency.