Scaled Metric Surprises on iOS & iPadOS
UIKit’s UIFontMetrics.scaledValue(for:) and SwiftUI’s @ScaledMetric property wrapper offer third-party developers a public means to scale arbitrary design reference values up and down relative to dynamic type size changes. Please be aware, however, that scaled values are not scaled proportionally with the default point sizes of the related text style. They scale according to some other scaling function that differs considerably from the related text style. An example will help illustrate this. Consider the following code:
let metrics = UIFontMetrics(forTextStyle: .body)
let size = metrics.scaledValue(for: 17.0)
If the device is set to the .large dynamic type setting, the identity value is returned (size == 17.0). If you then downscale the device’s dynamic type size setting to .medium, one might expect the returned value to be 16.0. After all, the default system .body font size at .large is exactly 17.0, and the default .body font size at .medium is exactly 16.0. But instead, this is what happens:
// current dynamic type size setting is .medium...
let metrics = UIFontMetrics(forTextStyle: .body)
let size = metrics.scaledValue(for: 17.0)
// size == 16.333...
The divergence is even more pronounced the further up/down the dynamic type size range one goes:
The red text in each pairing the above is the system default .body font, and the black text is a system body font obtained using a ScaledMetric:
@ScaledMetric(relativeTo: .body) var scaled = 17.0
var body: some View {
Text("Quick, brown fox.")
.foregroundStyle(.red)
.font(.body)
.overlay {
Text("Quick, brown fox.")
.foregroundStyle(.black)
.font(.system(size: scaled))
}
}
So if you need to scale a bit of UI in exact proportion to the .body font size, avoid using ScaledMetric/UIFontMetrics scaling APIs and instead directly obtain the pointSize from a system body font and use that value instead:
UIFont.preferredFont(
forTextStyle: .body,
compatibleWith: traitCollection
).pointSize
(EDITED: An earlier version of this post included an erroneous assumption that has been living rent-free in my brain for years. Thanks to Matthias for the clarification.)
Dagmar Chili Pitas & Doxowox: Now With Slightly-Less Unofficial Mirrors
It is with great pleasure that I share that the following two Internet classics have been brought back to life at their own blessed domain names, with TLS and everything, honest to God 21st century websites:
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Dagmar Chili Pitas, the Two-Year Chili, demonstrably the peak of what’s possible with Hypertext Markup Language as a medium. The original domain name (dagmarchili.pitas.com) wasn’t available. In the years since The Chili went offline, pitas.com has changed hands. It’s replacement uses a hyphenated URL instead. ….the enemy of the good and all that.
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Doxowox, the older sibling to The Chili, a beloved precursor, has also been resurrected. Enjoy!
Reader please note: these are not my writings, but I am honored to steward their continued presence on the Internet. They are works of art and deserve grace and aesthetic elbow room.
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Deep Fake
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Deep Fake
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Mustang
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