flashlight: Add multiple display modes

[vkareh]

Adds various modes to the flashlight app:

• Off
• Red (night mode)
• White (normal)
• Strobe (safety/emergency signaling)

Tapping the screen cycles through these modes. This makes it behave more like standard headlamps or safety hiking/cycling lights, with the first mode always red to not affect your pupils in the dark.

Note: The strobe looks strange in the animation because of the InfiniSim refresh rate. It looks better on the real watch, since it turns the backlight on and off directly.

Also the strobe is 2Hz at 20% duty cycle (100ms on, 400ms off), which provides good visibility from a distance and is low enough that it won't trigger people with photosensitive epilepsy.

[github-actions]

Build size and comparison to main:

Section	Size	Difference
text	383100B	320B
data	944B	0B
bss	22632B	0B

Run in InfiniEmu

[Andersama]

What would you think about adding an option for an SOS indicator in addition to the strobe? Shouldn't be much different from the strobe option, just an additional amount of memory for a small state machine.

[vkareh]

@Andersama

What would you think about adding an option for an SOS indicator in addition to the strobe? Shouldn't be much different from the strobe option, just an additional amount of memory for a small state machine.

To be honest, I don't think the display refresh is fast enough for this. At best you'd get something that looks like a random pattern blinker... I played with different frequencies, duty cycles, and patterns, and none of them look like what you'd expect from a simple hardware-controlled LED...

[vkareh]

🤦 doh! Of course! As soon as I said "simple hardware-controlled LED", it dawned on me that redrawing the screen between black and white is kind of pointless if I can just set the screen as white and just turn it on-and-off at the hardware level. So I did that and the strobe is significantly nicer now.

Also I was able to get a somewhat reasonable SOS signal:

sos-strobe.mp4

(but I haven't pushed that change yet - maybe if more folks think it's a good idea I can add it?)