新增業務邏輯

據推測，你的程式會做點什麼。將你的工作程式碼新增到專案中以代替 Program.fs。在這種情況下，我們的任務是在 Window Canvas 上繪製螺旋曲線。這是使用下面的 Spirograph.fs 完成的。

namespace Spirograph

// open System.Windows does not automatically open all its sub-modules, so we 
// have to open them explicitly as below, to get the resources noted for each.
open System                             // for Math.PI
open System.Windows                     // for Point
open System.Windows.Controls            // for Canvas
open System.Windows.Shapes              // for Ellipse
open System.Windows.Media               // for Brushes

// ------------------------------------------------------------------------------
// This file is first in the build sequence, so types should be defined here
type DialogBoxXaml  = FsXaml.XAML<"DialogBox.xaml">
type MainWindowXaml = FsXaml.XAML<"MainWindow.xaml">
type App            = FsXaml.XAML<"App.xaml"> 

// ------------------------------------------------------------------------------
// Model: This draws the Spirograph
type MColor = | MBlue   | MRed | MRandom

type Model() =
  let mutable myCanvas: Canvas = null
  let mutable myR              = 220    // outer circle radius
  let mutable myr              = 65     // inner circle radius
  let mutable myl              = 0.8    // pen position relative to inner circle
  let mutable myColor          = MBlue  // pen color
  
  let rng                      = new Random()
  let mutable myRandomColor    = Color.FromRgb(rng.Next(0, 255) |> byte,
                                               rng.Next(0, 255) |> byte,
                                               rng.Next(0, 255) |> byte)

  member this.MyCanvas
    with get() = myCanvas
    and  set(newCanvas) = myCanvas <- newCanvas

  member this.MyR
    with get() = myR
    and  set(newR) = myR <- newR

  member this.Myr
    with get() = myr
    and  set(newr) = myr <- newr

  member this.Myl
    with get() = myl
    and  set(newl) = myl <- newl

  member this.MyColor
    with get() = myColor
    and  set(newColor) = myColor <- newColor

  member this.Randomize =
    // Here we randomize the parameters. You can play with the possible ranges of
    // the parameters to find randomized spirographs that are pleasing to you.
    this.MyR      <- rng.Next(100, 500)
    this.Myr      <- rng.Next(this.MyR / 10, (9 * this.MyR) / 10)
    this.Myl      <- 0.1 + 0.8 * rng.NextDouble()
    this.MyColor  <- MRandom
    myRandomColor <- Color.FromRgb(rng.Next(0, 255) |> byte,
                                   rng.Next(0, 255) |> byte,
                                   rng.Next(0, 255) |> byte)

  member this.DrawSpirograph =
    // Draw a spirograph. Note there is some fussing with ints and floats; this 
    // is required because the outer and inner circle radii are integers. This is
    // necessary in order for the spirograph to return to its starting point 
    // after a certain number of revolutions of the outer circle.
    
    // Start with usual recursive gcd function and determine the gcd of the inner
    // and outer circle radii. Everything here should be in integers.
    let rec gcd x y =
        if y = 0 then x
        else gcd y (x % y)
  
    let g = gcd this.MyR this.Myr             // find greatest common divisor
    let maxRev = this.Myr / g                 // maximum revs to repeat

    // Determine width and height of window, location of center point, scaling 
    // factor so that spirograph fits within the window, ratio of inner and outer
    // radii.
    
    // Everything from this point down should be float.
    let width, height = myCanvas.ActualWidth, myCanvas.ActualHeight
    let cx, cy = width / 2.0, height / 2.0    // coordinates of center point
    let maxR   = min cx cy                    // maximum radius of outer circle
    let scale  = maxR / float(this.MyR)             // scaling factor
    let rRatio = float(this.Myr) / float(this.MyR)  // ratio of the radii

    // Build the collection of spirograph points, scaled to the window.
    let points = new PointCollection()
    for degrees in [0 .. 5 .. 360 * maxRev] do
      let angle = float(degrees) * Math.PI / 180.0
      let x, y = cx + scale * float(this.MyR) *
                 ((1.0-rRatio)*Math.Cos(angle) +
                  this.Myl*rRatio*Math.Cos((1.0-rRatio)*angle/rRatio)),
                 cy + scale * float(this.MyR) *
                 ((1.0-rRatio)*Math.Sin(angle) - 
                  this.Myl*rRatio*Math.Sin((1.0-rRatio)*angle/rRatio))
      points.Add(new Point(x, y))
  
    // Create the Polyline with the above PointCollection, erase the Canvas, and 
    // add the Polyline to the Canvas Children
    let brush = match this.MyColor with
                | MBlue   -> Brushes.Blue
                | MRed    -> Brushes.Red
                | MRandom -> new SolidColorBrush(myRandomColor)
  
    let mySpirograph = new Polyline()
    mySpirograph.Points <- points
    mySpirograph.Stroke <- brush

    myCanvas.Children.Clear()
    this.MyCanvas.Children.Add(mySpirograph) |> ignore

Spirograph.fs 是編譯順序中的第一個 F#檔案，因此它包含我們需要的型別的定義。它的工作是根據在對話方塊中輸入的引數在主視窗 Canvas 上繪製一個螺旋形圖。由於有很多關於如何繪製肺活量計的參考文獻，我們在此不再贅述。