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Rumor has it that Apple will support the Apple Pencil in the forthcoming iPad. If so, more developers will want to use the new features of UITouch — force, angle, and elevation — supported by the incredibly-precise stylus.
Basically, it’s trivial:
— Force is UITouch.Force;
— Angle is UITouch.GetAzimuthAngle(UIView); and
— Angle above horizontal is UITouch.AltitudeAngle
(The UIView objects are there, I think, to make it easier to create a custom angular transform that is more natural to the task at hand — i.e., an artist could “rotate” the page slightly to accommodate the angle with which they like to work. I think.)
Anyhow, here’s some code:
namespace UITouch0 open System open UIKit open Foundation open System.Drawing open CoreGraphics type ContentView(color : UIColor) as this = inherit UIView() do this.BackgroundColor <- color let MaxRadius = 200.0 let MaxStrokeWidth = nfloat 10.0 //Mutable! member val Circle : (CGPoint * nfloat * nfloat * nfloat ) option = None with get, set member this.DrawTouch (touch : UITouch) = let radius = (1.0 - (float touch.AltitudeAngle) / (Math.PI / 2.0)) * MaxRadius |> nfloat this.Circle <- Some (touch.LocationInView(this), radius, touch.GetAzimuthAngle(this), touch.Force) this.SetNeedsDisplay() override this.Draw rect = match this.Circle with | Some (location, radius, angle, force) -> let rectUL = new CGPoint(location.X - radius, location.Y - radius) let rectSize = new CGSize(radius * (nfloat 2.0), radius * (nfloat 2.0)) use g = UIGraphics.GetCurrentContext() let strokeWidth = force * MaxStrokeWidth g.SetLineWidth(strokeWidth) let hue = angle / nfloat (Math.PI * 2.0) let color = UIColor.FromHSB(hue, nfloat 1.0, nfloat 1.0) g.SetStrokeColor(color.CGColor) g.AddEllipseInRect <| new CGRect(rectUL, rectSize) g.MoveTo (location.X, location.Y) let endX = location.X + nfloat (cos(float angle)) * radius let endY = location.Y + nfloat (sin(float angle)) * radius g.AddLineToPoint (endX, endY) g.StrokePath() | None -> ignore() type SimpleController() = inherit UIViewController() override this.ViewDidLoad() = this.View <- new ContentView(UIColor.Blue) override this.TouchesBegan(touches, evt) = let cv = this.View :?> ContentView touches |> Seq.map (fun o -> o :?> UITouch) |> Seq.iter cv.DrawTouch override this.TouchesMoved(touches, evt) = let cv = this.View :?> ContentView touches |> Seq.map (fun o -> o :?> UITouch) |> Seq.iter cv.DrawTouch [<Register("AppDelegate")>] type AppDelegate() = inherit UIApplicationDelegate() let window = new UIWindow(UIScreen.MainScreen.Bounds) override this.FinishedLaunching(app, options) = let viewController = new SimpleController() viewController.Title <- "F# Rocks" let navController = new UINavigationController(viewController) window.RootViewController <- navController window.MakeKeyAndVisible() true module Main = [<EntryPoint>] let main args = UIApplication.Main(args, null, "AppDelegate") 0
And it looks like this:
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