Clip geometry

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// Copyright 2022 Esri
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import ArcGIS
import SwiftUI

struct ClipGeometryView: View {
    /// A Boolean value indicating whether the geometries are clipped.
    @State private var geometriesAreClipped = false

    /// The view model for the sample.
    @StateObject private var model = Model()

    var body: some View {
        MapView(map: model.map, graphicsOverlays: model.graphicsOverlays)
            .toolbar {
                ToolbarItem(placement: .bottomBar) {
                    Button(geometriesAreClipped ? "Reset" : "Clip") {
                        if geometriesAreClipped {
                            model.reset()
                        } else {
                            model.clipGeometries()
                        }
                        geometriesAreClipped.toggle()
                    }
                }
            }
    }
}

private extension ClipGeometryView {
    /// The model used to store the geo model and other expensive objects
    /// used in this view.
    class Model: ObservableObject {
        /// A map with a topographic basemap style and an initial viewpoint of Colorado.
        let map: Map = {
            let map = Map(basemapStyle: .arcGISTopographic)
            // Sets the initial viewpoint to Colorado and adds additional padding.
            map.initialViewpoint = Viewpoint(boundingGeometry: .coloradoEnvelope.expanded(by: 2))
            return map
        }()

        /// The graphics overlay containing an unclipped graphic of Colorado.
        private let coloradoGraphicsOverlay = GraphicsOverlay(
            graphics: [
                Graphic(geometry: .coloradoEnvelope, symbol: .coloradoFill)
            ]
        )

        /// The graphics overlay containing graphics of the other envelopes, outlined by a dotted red line.
        private let envelopesGraphicsOverlay = GraphicsOverlay(
            graphics: Geometry.envelopes.map {
                Graphic(geometry: $0, symbol: SimpleLineSymbol(style: .dot, color: .red, width: 3))
            }
        )

        /// The graphics overlay containing clipped graphics.
        private let clippedGraphicsOverlay = GraphicsOverlay()

        /// The unclipped graphic of Colorado.
        private var coloradoGraphic: Graphic { coloradoGraphicsOverlay.graphics.first! }

        /// The graphics overlays used in this sample.
        var graphicsOverlays: [GraphicsOverlay] {
            return [coloradoGraphicsOverlay, envelopesGraphicsOverlay, clippedGraphicsOverlay]
        }

        /// Clips the geometry of Colorado to the given envelope.
        /// - Parameter envelope: The envelope to clip the geometry of Colorado to.
        /// - Returns: The clipped graphic.
        private func clipColoradoGeometry(to envelope: Envelope) -> Graphic {
            // Uses the geometry engine to create a new geometry for the area of
            // Colorado that overlaps the given envelope.
            let clippedGeometry = GeometryEngine.clip(coloradoGraphic.geometry!, to: envelope)
            // Creates and returns the clipped graphic from the clipped geometry if there is an overlap.
            return Graphic(geometry: clippedGeometry, symbol: .coloradoFill)
        }

        /// Clips geometries and adds resulting graphics.
        func clipGeometries() {
            // Hides the Colorado graphic.
            coloradoGraphic.isVisible = false
            // Clips Colorado's geometry to each envelope.
            let clippedGraphics = envelopesGraphicsOverlay.graphics.map { clipColoradoGeometry(to: $0.geometry as! Envelope) }
            // Adds the clipped graphics.
            clippedGraphicsOverlay.addGraphics(clippedGraphics)
        }

        /// Removes all clipped graphics.
        func reset() {
            clippedGraphicsOverlay.removeAllGraphics()
            coloradoGraphic.isVisible = true
        }
    }
}

private extension Symbol {
    /// The simple fill symbol for Colorado graphics.
    static var coloradoFill: SimpleFillSymbol {
        SimpleFillSymbol(
            color: .blue.withAlphaComponent(0.2),
            outline: SimpleLineSymbol(
                style: .solid,
                color: .blue,
                width: 2
            )
        )
    }
}

private extension Geometry {
    /// An envelope approximating the boundary of Colorado.
    static var coloradoEnvelope: Envelope {
        Envelope(
            xMin: -11362327.1283,
            yMin: 5012861.2903,
            xMax: -12138232.0184,
            yMax: 4441198.7738,
            spatialReference: .webMercator
        )
    }
    /// An envelope inside the boundary of Colorado.
    static var containedEnvelope: Envelope {
        Envelope(
            xMin: -11655182.5952,
            yMin: 4741618.773,
            xMax: -11431488.567,
            yMax: 4593570.0683,
            spatialReference: .webMercator
        )
    }
    /// An envelope intersecting the boundary of Colorado.
    static var intersectingEnvelope: Envelope {
        Envelope(
            xMin: -11962086.4793,
            yMin: 4566553.8814,
            xMax: -12260345.1836,
            yMax: 4332053.3784,
            spatialReference: .webMercator
        )
    }
    /// An envelope outside the boundary of Colorado.
    static var outsideEnvelope: Envelope {
        Envelope(
            xMin: -11858344.3213,
            yMin: 5147942.2252,
            xMax: -12201990.2197,
            yMax: 5297071.5773,
            spatialReference: .webMercator
        )
    }
    /// The envelopes to clip the geometry of Colorado to.
    static var envelopes: [Envelope] {
        return [.containedEnvelope, .intersectingEnvelope, .outsideEnvelope]
    }
}

private extension Envelope {
    /// Expands the envelope by a given factor.
    func expanded(by factor: Double) -> Envelope {
        let builder = EnvelopeBuilder(envelope: self)
        builder.expand(by: factor)
        return builder.toGeometry()
    }
}

#Preview {
    NavigationStack {
        ClipGeometryView()
    }
}