Draft: Improve femtovg rendering on high-DPI displays #9310
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Related also #2618 |
This was referenced Sep 8, 2025
tronical
reviewed
Sep 15, 2025
| // dpi / device pixel ratio as the anti-alias of femtovg needs that to draw text clearly. | ||
| // We need to care about that `ceil()` when calculating metrics. | ||
| femtovg_canvas.set_size(surface_size.width, surface_size.height, scale); | ||
| femtovg_canvas.set_size(surface_size.width, surface_size.height, 1.0); |
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This reverts #2618 more or less. I was under the impression that it looked better, but from the amount of reports and your testing it looks like that isn't universally the case. I'm okay with reverting back to what you're proposing, but I think the comment before this function call needs adjusting.
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I don't believe that this is still relevant after the recent fontique and parley changes. |
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DO NOT MERGE
This is a complete draft and I do not know what I'm doing.
Related to #6298 #6215 #5748 afaik.
What seems to be happening is that slint is doing its own handling of monitor scale factors/DPI scales greater than 1. At the same time, there's code in femtovg to handle this, but the logic is either somewhat botched or unaware of what slint is already doing. Such that if slint is already handling a scale factor of e.g. 1.5, then that is mistakenly being multiplied by another 1.5 in femtovg to produce a value of 2.25 that's doing something bad somewhere. Or something.
My changes here just remove the scale passed to femtovg and hardcode a value of
1.0instead.Regardless, compare how the bevy example looks on my 1.566667 scale factor laptop monitor before and after this change. You might need to download the file and view it 1:1 to properly see the difference:
Even if this is indeed the correct solution here (I doubt it) then more cleanup work is needed.