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Resolved font sizes include the layout's display scale, and that scaled size was passed to HarfRust as the point size. The AAT `trak` table's tracking is looked up by point size, so on a 2x display text got the tracking for twice its size (for San Francisco: negative tracking at 11px instead of positive). `ShapeOptions` now has a `point_size` that Parley sets to the font size before display scaling.
DJMcNab
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Nov 5, 2026
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Conceptually, I agree that this change is correct. The way this PR is structured made me need to research to work out what it's actually doing - I've made suggestions inline to more closely match my mental model.
It also isn't self-evident that storing the physical font size and then dividing it back out by the scale to get the logical font size is the right shape for this, although arguably that could just be kept as a todo?
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| // Resolved font sizes include the display scale, but size-dependent shaping (such as `trak`) | ||
| // must use the unscaled point size. |
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Suggested change
| // Resolved font sizes include the display scale, but size-dependent shaping (such as `trak`) | |
| // must use the unscaled point size. |
I don't find the term "unscaled point size" to be a self-explanatory phrase, and this isn't something subtle which requires a comment.
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| /// The font size to shape the item with. | ||
| pub font_size: f32, | ||
| /// The font size in points (CSS pixels), before any display scaling. | ||
| /// | ||
| /// Used by size-dependent shaping, such as the AAT `trak` table's tracking. This usually | ||
| /// equals `font_size` unless that has been multiplied by a display scale factor. | ||
| pub point_size: f32, |
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I'd like to see this changed to something like:
Suggested change
| /// The font size to shape the item with. | |
| pub font_size: f32, | |
| /// The font size in points (CSS pixels), before any display scaling. | |
| /// | |
| /// Used by size-dependent shaping, such as the AAT `trak` table's tracking. This usually | |
| /// equals `font_size` unless that has been multiplied by a display scale factor. | |
| pub point_size: f32, | |
| /// The font size to shape the item with. | |
| /// | |
| /// This is a number of device/physical points, i.e. the logical font size | |
| /// multiplied by any active scale factor. | |
| pub font_size: f32, | |
| /// The logical font size in points (CSS pixels), i.e. ignoring . | |
| /// | |
| /// Used by size-dependent shaping, such as the AAT `trak` table's tracking. | |
| pub point_size: f32, |
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The AAT
traktable's tracking is looked up by the unscaled (logical pixel) font size, so we need to pass that size rather the scale (physical pixel) font size to HarfRust.Screenshot
Changelog