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Comment by sho_hn | Hacker News Reader

In KDE Plasma we've supported the way you like for quite some years, because Qt is a cross-platform toolkit that supported fractional on e.g. Windows already and we just went ahead and put the mechanisms in place to make use of that on Wayland.

The standardized protocols are more recent (and of course we heavily argued for them).

Regarding the way the protocol works and something having to be retrofitted, I think you are maybe a bit confused about the way the scale factor and buffer scale work on wl_output and wl_surface?

But in any case, yes, I think the happy camper days are coming for you! I also find the macOS approach attrocious, so I appreciate the sentiment.

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Thanks! By retrofitting I mean having to have a new protocol with this new opt-in method where some apps will be getting integer scales and go through a transform and some apps will be getting a fractional scale and rendering directly to the output resolution. If this had worked "correctly" from the start the compositors wouldn't even need to know anything about scaling. As far as they knew the scaling metadata could have been an opaque value that they passed from the user config to the clients to figure out. I assume we're stuck forever with all compositors having to understand all this instead of just punting the problem completely to clients.

When you say you supported this for quite some years was there a custom protocol in KWin to allow clients to render directly to the fractionally scaled resolution? ~4 years ago I was frustrated by this when I benchmarked a 2x slowdown from RAW file to the same number of pixels on screen when using fractional scaling and at least in sway there wasn't a way to fix it or much appetite to implement it. It's great to see it is mostly in place now and just needs to be enabled by all the stack.

Oh, ok. Yeah, this I agree with, and I think plenty of people do - having integer-only scaling in the core protocol at the start was definitely a regretable oversight and is a wart on things.

> When you say you supported this for quite some years was there a custom protocol in KWin to allow clients to render directly to the fractionally scaled resolution?

Qt had a bunch of different mechanisms for how you could tell it to use a fractional scale factor, from setting an env var to doing it inside a "platform plugin" each Qt process loads at runtime (Plasma provides one), etc. We also had a custom-protocol-based mechanism (zwp_scaler_dev iirc) that basically had a set_scale with a 'fixed' instead of an 'int'. Ultimately this was all pretty Qt-specific though in practice. To get adoption outside of just our stack a standard was of course needed, I guess what we can claim though is that we were always pretty firm we wanted proper fractional and to put in the work.

Thank you for that. The excellent fractional scaling and multi-monitor support is why I finally switched back to KDE full time (after first switching away during the KDE 3 to 4 mess).

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