more ui jumpiness

mac/Sources/Byre/Format.swift

@@ -250,14 +250,104 @@ struct PreBox: View {
 
 struct Spinner: View {
     var color: Color
-    private static let frames = Array("⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏")
+    @Environment(\.font) private var font
+    @Environment(\.fontResolutionContext) private var fontContext
 
     var body: some View {
-        TimelineView(.periodic(from: .now, by: 0.08)) { context in
+        Text("⠋")
-            let i = Int(context.date.timeIntervalSinceReferenceDate / 0.08) % Self.frames.count
+            .hidden()
-            Text(String(Self.frames[i]))
+            .overlay {
-                .foregroundStyle(color)
+                SpinnerGlyphs(font: (font ?? .body).resolve(in: fontContext).ctFont, color: color)
+                    .allowsHitTesting(false)
+            }
+    }
+}
+
+private struct SpinnerGlyphs: NSViewRepresentable {
+    let font: CTFont
+    let color: Color
+
+    func makeNSView(context: Context) -> SpinnerView {
+        SpinnerView()
+    }
+
+    func updateNSView(_ v: SpinnerView, context: Context) {
+        v.font = font
+        v.color = color.resolve(in: context.environment).cgColor
+        v.needsLayout = true
+    }
+}
+
+private final class SpinnerView: NSView {
+    private struct Key: Equatable {
+        let size: CGSize
+        let scale: CGFloat
+        let font: CTFont
+        let color: CGColor
+    }
+
+    private static let frames = Array("⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏")
+    var font: CTFont?
+    var color: CGColor?
+    private let glyph = CALayer()
+    private var drawn: Key?
+
+    override init(frame: NSRect) {
+        super.init(frame: frame)
+        wantsLayer = true
+        layer?.addSublayer(glyph)
+    }
+
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) is not supported")
+    }
+
+    override func viewDidChangeBackingProperties() {
+        super.viewDidChangeBackingProperties()
+        needsLayout = true
+    }
+
+    override func layout() {
+        super.layout()
+        guard let font, let color, let window, bounds.width > 0, bounds.height > 0 else {
+            return
         }
+        let key = Key(size: bounds.size, scale: window.backingScaleFactor, font: font, color: color)
+        if key == drawn {
+            return
+        }
+        drawn = key
+        let images = Self.frames.map { render(String($0), key) }
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
+        glyph.frame = bounds
+        glyph.contentsScale = key.scale
+        glyph.contents = images[0]
+        let spin = CAKeyframeAnimation(keyPath: "contents")
+        spin.values = images
+        spin.keyTimes = (0...images.count).map { NSNumber(value: Double($0) / Double(images.count)) }
+        spin.calculationMode = .discrete
+        spin.duration = 0.08 * Double(images.count)
+        spin.repeatCount = .infinity
+        spin.isRemovedOnCompletion = false
+        glyph.add(spin, forKey: "spin")
+        CATransaction.commit()
+    }
+
+    private func render(_ s: String, _ key: Key) -> CGImage {
+        let ctx = CGContext(data: nil, width: Int(ceil(key.size.width * key.scale)), height: Int(ceil(key.size.height * key.scale)), bitsPerComponent: 8, bytesPerRow: 0, space: CGColorSpace(name: CGColorSpace.sRGB)!, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!
+        ctx.scaleBy(x: key.scale, y: key.scale)
+        let attrs: [NSAttributedString.Key: Any] = [
+            NSAttributedString.Key(kCTFontAttributeName as String): key.font,
+            NSAttributedString.Key(kCTForegroundColorAttributeName as String): key.color,
+        ]
+        let line = CTLineCreateWithAttributedString(NSAttributedString(string: s, attributes: attrs))
+        var ascent: CGFloat = 0
+        var descent: CGFloat = 0
+        let width = CTLineGetTypographicBounds(line, &ascent, &descent, nil)
+        ctx.textPosition = CGPoint(x: (key.size.width - width) / 2, y: (key.size.height - ascent - descent) / 2 + descent)
+        CTLineDraw(line, ctx)
+        return ctx.makeImage()!
     }
 }