Why does my Mac slow down when the volume/brightness indicator fades out?

I frequently change the volume and brightness on my computer. Usually I modify them to more or less match my surrounding physical(!) environment. But there's this one annoying quirk with changing my volume and brightness.

When the brightness/volume indicator – I'm referring to this thing, by the way:

..fades out, my entire computer's frame rate just seems to drop. For example when I'm playing Minecraft and I'm changing my brightness or volume, the FPS drops down to about 10 from 110. YouTube videos also go from 60FPS to around a few frames per second.

Any idea what the cause of this is? It seems to be consistent across different Macs, too – I get the same issue on a new MacBook Pro.

What kind of OS X version that you are running? (Yosemite or El Capitan? I see in screenshot posted a volume/brightness indicator)

It sounds LIKE a good idea when you talking about Mac slow down when volume/brightness indicator fades out.

Here to fix this:

Go to System Preferences > Accessibility and then check "Increase Contrast" Option.

Also you can watch this video to fix about Slow Macs: https://www.youtube.com/watch?v=hi5VJsbRxzk

Same problem on my 2008 Mac Pro too, But i'm sorry that for didn't answer for a long, I am a first user using this forum, But People who don't know what problem this is.