Graduated transition when setting brightness

[akiva]

Would it be possible to implement an option to transition the fade when setting, ie. brightnessctl set 5%-, so that it's more aesthetically pleasing and feels less clunky as it steps up or down?

[Hummer12007]

Sure! It's an awesome idea. I'll definitely merge a PR.

If you're up to it, I'd be glad to discuss the implementation with you.

[akiva]

I would be happy to try and help with this—it would be my first c-based PR. Would you care to provide any implementation tips here or in e-mail? Cheers!

[Hummer12007]

Great!
You will roughly need to do the following:

• Add an option for transition duration (0 by default)
• An example of a way to implement smooth transition would be: when the transition duration is non-zero, you can split the duration into equal chunks (|d->curr_brightness - new| chunks to be precise, https://github.com/Hummer12007/brightnessctl/blob/master/brightnessctl.c#L325) , and increment/decrement the brightness, writing the new value on each chunk.

I'd also like you to consider what would happen if a user executes multiple instances of smooth transition concurrently, and how/whether we'd need to handle that.

[CameronNemo]

FWIW my project brillo implements this feature. Most of the functionality to enable it is concentrated in this file (note: this is 0BSD now).

Some tips from my experience:

• You need to decide on a sleep interval at which to write to the brightness file, and if it is too rapid udevd will eat up a lot of resources. I used 100 writes per second; you may not need this many.
• You will need to write at each interval, then flush the write data (if applicable), then sleep the remaining time in the interval.
• You will need to check the clock before and after each write. The write may take some time, so you will need to subtract the difference from the sleep interval duration.

Best of luck!

[dirdi]

This would be a really nice feature. Unfortunately my C skills are very limited, so I can not provide a PR. However, I wrote this short BASH script that does the job:

I=0
while [ $I -lt 10 ]; do
    brightnessctl -c backlight -q s 2%-
    sleep 0.05
    ((I = I + 1));
done

Adjust the values to fit your needs.

[Hummer12007]

There's some work-in-progress code in the anim branch, I think there are a few concurrency left to be resolved.