Wayland pain points – kgamma

In the feedback about dropping X11 support, one very surprisingly common comment is from users saying they "need" kgamma, a simple tool that allows the user to adjust the gamma, red, blue and green that gets drawn to the screen operating directly on the X server.

On our Wayland session we have colour management that blows simple gamma adjustment out of the water, so on the face of it it seems weird that this would come up. However at the same time, I get it. ICC profiles are very confusing and it's not the same as a few basic sliders that anyone can understand.

We want people to have the best transition to Wayalnd we can offer and this is a relatively easy fix.

The new tool

I have made a simple tool that edits the relevant part of an ICC profile - VCGTs.

"VCGT (Video Card Gamma Table): An optional, private tag inside an ICC file that stores 1D grayscale/gamma curves loaded directly into your graphics card's hardware Look-Up Table (LUT)."

That's a lot of fancy terms, but the key point is it's a tiny subset of the thing Kwin already supports. We can add a UI around those few values and not need to add a second code path in kwin or kscreen.

The UX is deliberately similar to the old UI.
Obviously it needs a round of polish (volunteers welcome!), but it's functional.

Why this is even better than on X11

Unlike KGamma on X11, this new tool:

  • Supports multiple monitors with independent values

  • Works with night colour rather than fighting over the same settings, Kwin will blend the two sets on top of each other

  • Gets applied by Kwin on startup so the first frame is perfect, rather than glitching during loading

What next

Whilst changing your red/green settings wtih sliders might be something a few users do, and we got a few comments it remains a niche case.
My intention is to post it as a standalone application on Flathub and not as part of Plasma. I think that strikes the right balance of providing support without holding ourselves back longterm.

Getting it

The new tool is available at:

https://invent.kde.org/davidedmundson/kgamma2

Usual CMake + build instructions apply.

Feel free to make pull requests and let me know if it helps solve your issue!