ZStackにおけるViewについて考察する(004,ジェスチャのコードをメソッド化する)

import SwiftUI

struct ContentView: View {

    let RECT_W: CGFloat = 320
    let RECT_H: CGFloat = 640

    let COLOR_RECT: Color = Color.blue
    let COLOR_TEXT: Color = Color.white

    let COLOR_INSIDE: Color = Color( red: 0x00, green: 0xff, blue: 0x00, opacity: 0xff )
    let COLOR_OUTSIDE: Color = Color( red: 0xff, green: 0x00, blue: 0x00, opacity: 0xff )

    let CURSOR_COLOR: Color = Color.yellow
    let CURSOR_LINE_WIDTH: CGFloat = 3.0

    @State var Tap = CGPoint( x: 0.0, y: 0.0 )
    @State var InsideRectTap = CGPoint( x: 0.0, y: 0.0 )

    @State var FlagInsideRect = true

    var body: some View {

        ZStack{

            // 最背面.
            Rectangle()
                .foregroundColor( FlagInsideRect ? COLOR_INSIDE : COLOR_OUTSIDE )

            // 中層面.
            Rectangle()
                .frame( width: RECT_W, height: RECT_H ) // サイズを指定する.
                .foregroundColor( COLOR_RECT ) // 色を指定する.
                .onTapGesture { tap in
                    Tap = tap
                    let rct = CGSize( width: RECT_W, height: RECT_H )
                    getInsideRectTapPoint( &InsideRectTap, &FlagInsideRect, Tap, rct )
                }
                .gesture(
                    DragGesture( minimumDistance: 0 )
                        .onChanged{ tap in
                            Tap = tap.location // ここは tap の location.
                            let rct = CGSize( width: RECT_W, height: RECT_H )
                            getInsideRectTapPoint( &InsideRectTap, &FlagInsideRect, Tap, rct )
                        }
                        .onEnded { tap in
                            Tap = tap.location // ここは tap の location.
                            let rct = CGSize( width: RECT_W, height: RECT_H )
                            getInsideRectTapPoint( &InsideRectTap, &FlagInsideRect, Tap, rct )
                        }
                    )

            // 十字カーソルを描画する.
            Path { path in

                let the_x = InsideRectTap.x
                let the_y = InsideRectTap.y

                // 始点から終点にむかって線分を引く(垂直線).
                path.move(to: CGPoint(x: the_x, y: 0 ))
                path.addLine(to: CGPoint(x: the_x, y: RECT_H ))

                // 始点から終点にむかって線分を引く(水平線).
                path.move(to: CGPoint(x: 0, y: the_y ))
                path.addLine(to: CGPoint(x: RECT_W, y: the_y ))

            }
            .stroke( CURSOR_COLOR, lineWidth: CURSOR_LINE_WIDTH )
            .frame( width: RECT_W, height: RECT_H )

            // 最前面.
            VStack{

                Text( String( format: "Rectangle WH %.1f * %.1f", RECT_W, RECT_H ))
                    .foregroundColor( COLOR_TEXT )
                Text( String( format: "TapXY( %.1f, %.1f )", Tap.x, Tap.y ))
                    .foregroundColor( COLOR_TEXT )
                Text( String( format: "InsideRectTapXY( %.1f, %.1f )", InsideRectTap.x, InsideRectTap.y ))
                    .foregroundColor( COLOR_TEXT )
                Text( String( format: "FlagInsideRect is %d", FlagInsideRect ))
                    .foregroundColor( FlagInsideRect ? COLOR_INSIDE : COLOR_OUTSIDE )

            }

        }

    }

    // タップした座標が矩形内部に入っているか確認して矩形内部の座標として取得するメソッド.
    func getInsideRectTapPoint(
            _ inside_rect_tap: inout CGPoint,
            _ flag_inside_rect: inout Bool,
            _ tap: CGPoint,
            _ rect: CGSize
            )->Void{

        // いったんそのままタップ座標を代入する.
        inside_rect_tap.x = tap.x
        inside_rect_tap.y = tap.y

        // いったんフラグを真にしておく.
        flag_inside_rect = true

        // Rectangleの内側か外側か判定して inside_rect_tap.x と .y を調整する.
        if ( inside_rect_tap.x < 0.0 ){
            inside_rect_tap.x = 0.0
            flag_inside_rect = false
        }

        if ( inside_rect_tap.y < 0.0 ){
            inside_rect_tap.y = 0.0
            flag_inside_rect = false
        }

        if ( inside_rect_tap.x >= rect.width ){
            inside_rect_tap.x = rect.width - 1
            flag_inside_rect = false
        }

        if ( inside_rect_tap.y >= rect.height ){
            inside_rect_tap.y = rect.height - 1
            flag_inside_rect = false
        }

        return

    }

}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}