Gradually Decreasing Opacity Over Time

[5chw1]

Is it possible to have a gradually decreasing opacity, let say minus 20 per second and stop the decrease once 0 is reach.
I will be using this idea to “if music is stopped or paused, it will gradually decrease and set it to 100 opacity if music is playing”.

[Ace]

If you’re using KLWP, you can simply use Animation > Fade Out. You can have that react to a Global Switch that is tied up to $mi(state)$.

[Nihilism]

This turned out to be much harder than I originally thought. I tried various combinations of tu and fl timers with no success, and then switched to try it with animations which also gave me problems with non-intuitive or weird behavior. However eventually I came up with a solution although probably better programmers can simplify or improve.

1/ Create an OVERLAY GROUP at the basic (top) level of your design.
2/ Create or move your image or shape items in the Overlap Group.
3/ In the Group options select Animation and press + to create a rule.
4/ Click on the center of the rule (to the right of ‘Disabled’) and select React On.
5/ Select FORMULA and then in the second line Formula type or paste:
$if(mi(state)=PLAYING,f,b)$
so if music is playing the animation will go forward, and any other option (stopped, paused, etc.) will reverse [1 can replace f, and 0 can replace b]).
6/ Select ACTION: Fade In
7/ Select EASE: Normal
8/ Select DURATION and convert to formula then paste:
$if(mi(state)=PLAYING,1,100)$
which sets the animation speed to immediate (1) and 100 (10 seconds) if not playing.
9/ Select DELAY, convert to formula and paste:
$if(mi(state)=PLAYING,0,10)$
which sets the animation delay when music starts to 0 and when the music stops to 10 (1 second).

Obviously you can change the duration and delay values to whatever you like. And that should do it, I hope. At least it works on my Android 14, Samsung A54 5G, UI One 6.

The formulas are required because I am unable to explain why it seems impossible, at least in my testing of dozens of combinations, to create one fade in animation rule with fixed duration and delay values, and a separate fade out animation rule with different fixed values. Possibly @frank or @Ace or someone better than me can do that.