VirtualDisplay/src/Resolution.swift

import Foundation

struct VDConfig: Equatable {
    let pixelWidth: Int
    let pixelHeight: Int
    let logicalWidth: Int
    let logicalHeight: Int
    let refreshRate: Int
}

let scalePercents: [Int] = [100, 125, 133, 150, 166, 175, 200]

let maxFramebufferPixelWidth  = 6144
let maxFramebufferPixelHeight = 3456

func vdConfig(physicalPixelWidth pw: Int,
              physicalPixelHeight ph: Int,
              refreshRate: Int,
              scalePercent s: Int) -> VDConfig {
    let lw = max(1, Int((Double(pw) * 100.0 / Double(s)).rounded()))
    let lh = max(1, Int((Double(ph) * 100.0 / Double(s)).rounded()))
    return VDConfig(
        pixelWidth:  lw * 2,
        pixelHeight: lh * 2,
        logicalWidth:  lw,
        logicalHeight: lh,
        refreshRate: refreshRate
    )
}

func availableScales(physicalPixelWidth pw: Int, physicalPixelHeight ph: Int) -> [Int] {
    return scalePercents.filter { s in
        let cfg = vdConfig(physicalPixelWidth: pw,
                           physicalPixelHeight: ph,
                           refreshRate: 60,
                           scalePercent: s)
        return cfg.pixelWidth  <= maxFramebufferPixelWidth
            && cfg.pixelHeight <= maxFramebufferPixelHeight
    }
}