[Submitted as FB22612121]
A SwiftUI Button using .buttonStyle(.glass) with .buttonBorderShape(.capsule) changes its background abruptly when its size goes from 50×50 to 51×51 points in dark mode. This appears to be a threshold in opacity/material rather than a smooth size-based change.
The sample shows identical buttons at 40, 50, 51, and 60 points, with a clear jump between 50 and 51. Measured RGB values shift from 19,19,19 to 30,30,30. The effect also varies with the background, which points to a material/opacity change rather than a fixed fill.
ENVIRONMENT
iOS 26.4.1 (23E254a)
iOS 26.5 (23F5059e)
REPRO STEPS
Create a new iOS SwiftUI project.
Replace ContentView with the sample code below.
Run the app or open ContentView in SwiftUI Preview (dark mode).
Observe the buttons at 40×40, 50×50, 51×51, and 60×60.
Compare the 50pt and 51pt buttons.
ACTUAL
The background changes abruptly between 50pt and 51pt. The 51pt button uses a noticeably different opacity/material, producing a visible jump in dark mode.
EXPECTED
The glass background should remain visually consistent or change smoothly as size changes by 1 point. 50pt and 51pt buttons should not have a discontinuous difference.
SCREENSHOT
SAMPLE CODE
struct ContentView: View {
private let sizes: [CGFloat] = [40, 50, 51, 60]
var body: some View {
ScrollView {
VStack(alignment: .leading, spacing: 16) {
Text("Glass button dark-mode size jump")
.font(.headline)
Text("All buttons use .buttonStyle(.glass). Only the label frame changes.")
.font(.footnote)
.foregroundStyle(.secondary)
ForEach(Array(sizes.enumerated()), id: \.offset) { index, size in
HStack(spacing: 14) {
Button {
} label: {
Text("\(index + 1)")
.font(.system(size: size * 0.42, weight: .medium))
.frame(width: size, height: size)
}
.buttonStyle(.glass)
.buttonBorderShape(.capsule)
Text("label frame: \(Int(size)) x \(Int(size))")
.font(.callout.monospacedDigit())
.foregroundStyle(.secondary)
}
}
}
.padding(24)
}
.preferredColorScheme(.dark)
}
}
