App Icon Generator — Swift source

// App Icon Generator — contain-fit, centered export geometry for the
// 16/32/180/192/512 icon set.
//
// Language: Swift (5.9, standard library only)
// Source:   CosmoDev polyglot showcase port, from the authored TypeScript
//           snippet src/tool-sources/app-icon-generator/typescript.ts.

/// One export target: the square canvas edge and the centered contain-fit
/// rect the source image is drawn into.
struct IconRect: Equatable, Sendable {
    let size: Int  // canvas edge (px x px)
    let x: Int, y: Int  // top-left offset: centers the fitted image
    let w: Int, h: Int  // fitted image size, at least 1x1
}

enum AppIconGeometry {

    static let defaultSizes = [16, 32, 180, 192, 512]

    /// The deterministic half of the tool: per export size, the contain-fit
    /// rect (scale = min(px/w, px/h), clamped to >= 1) plus the centered draw
    /// offset — the geometry the TS pipeline feeds `ctx.drawImage` before
    /// `canvas.toBlob` PNG-encodes each square. Bitmap decode and PNG encode
    /// stay with the host. `.rounded()` rounds half away from zero, matching
    /// JS `Math.round` on these non-negative values.
    static func iconSetPlan(srcW: Int, srcH: Int, sizes: [Int]? = nil) -> [IconRect] {
        let sizes = sizes ?? defaultSizes
        return sizes.map { px in
            let scale = min(Double(px) / Double(srcW), Double(px) / Double(srcH))
            let w = max(1, (Double(srcW) * scale).rounded())
            let h = max(1, (Double(srcH) * scale).rounded())
            return IconRect(
                size: px,
                x: Int(((Double(px) - w) / 2).rounded()),  // letterbox on transparency
                y: Int(((Double(px) - h) / 2).rounded()),
                w: Int(w),
                h: Int(h))
        }
    }
}