That's probably better than most scaling done on Wayland today because it's doing the rendering directly at the target resolution instead of doing the "draw at 2x scale and then scale down" dance that was popularized by OSX and copied by Linux. If you do it that way you both lose performance and get blurry output. The only corner case a compositor needs to cover is when a client is straddling two outputs. And even in…
> doing the "draw at 2x scale and then scale down" dance that was popularized by OSX Originally OS X defaulted to drawing at 2x scale without any scaling down because the hardware was designed to have the right number of pixels for 2x scale. The earliest retina MacBook Pro in 2012 for example was 2x in both width and height of the earlier non-retina MacBook Pro. Eventually I guess the cost of the hardware made this t…
That's an interesting related discussion. The idea that there is a physically correct 2x scale and fractional scaling is a tradeoff is not necessarily correct. First because different users will want to place the same monitor at different distances from their eyes, or have different eyesight, or a myriad other differences. So the ideal scaling factor for the same physical device depends on the user and the setup. But more importantly because having integer scaling be sharp and snapped to pixels and fractional scaling a tradeoff is mostly a software limitation. GUI toolkits can still place all ther UI at pixel boundaries even if you give them a target scaling of 1.785. They do need extra logic to do that and most can't. But in a weird twist of destiny the most used app these days is the browser and the rendering engines are designed to output at arbitrary factors natively and in most cases can't because the windowing system forces these extra transforms on them. 3D engines are another example, where they can output whatever arbitrary resolution is needed but aren't allowed to. Most games can probably get around that in some kind of fullscreen mode that bypasses the scaling.
I think we've mostly ignored these issues because computers are so fast and monitors have gotten so high resolution that the significant performance penalty (2x easily) and introduced blurryness mostly goes unnoticed.
> Take a look at this HiDPI rendering example in Leopard
That's a really cool example, thanks. At one point Ubuntu's Unity had a fake fractional scaling slider that just used integer scaling plus font size changes for the intermediate levels. That mostly works very well from the point of view of the user. Because of the current limitations in Wayland I mostly do that still manually. It works great for single monitor and can work for multiple monitors if the scaling factors work out because the font scaling is universal and not per output.