pamhagen-sysctrl/PamhagenSysCtrl/Helpers/Pipeline/FlowArrow.cs

using System.Diagnostics;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Shapes;

namespace PamhagenSysCtrl.Helpers.Pipeline {
    internal sealed class FlowArrow {

        private const double Speed = 45;
        private const double Spacing = 40;
        private const double HalfLength = 5;
        private const double HalfWidth = 3.5;

        private static readonly Stopwatch Clock = Stopwatch.StartNew();

        private readonly Canvas _layer;
        private readonly Point[] _path;
        private Point[] _points = [];
        private double _length;
        private double _pathOffset;
        private bool _isActive;

        public double Length => GetLength(_path[0], _path[1]) + GetLength(_path[1], _path[2]);

        private FlowArrow(Canvas canvas, Point[] path) {
            _path = path;
            _layer = new Canvas() {
                IsHitTestVisible = false,
                Visibility = Visibility.Collapsed,
            };
            _layer.Unloaded += (_, _) => Stop();
            canvas.Children.Add(_layer);
        }

        public static FlowArrow Create(Canvas canvas, Line first, Line second) {
            return new FlowArrow(canvas, [
                new Point(first.X1, first.Y1),
                new Point(first.X2, first.Y2),
                new Point(second.X2, second.Y2),
            ]);
        }

        public static FlowArrow Create(Canvas canvas, Polyline path) {
            return new FlowArrow(canvas, [.. path.Points]);
        }

        public void Update((bool TowardEnd, double PathOffset)? flow) {
            if (flow == null) {
                Stop();
                return;
            }

            var points = flow.Value.TowardEnd
                ? _path
                : [.. _path.Reverse()];
            var length = GetLength(points[0], points[1]) + GetLength(points[1], points[2]);
            if (length < 16) {
                Stop();
                return;
            }

            _points = points;
            _length = length;
            _pathOffset = flow.Value.PathOffset;
            if (!_isActive) {
                CompositionTarget.Rendering += OnRendering;
                _isActive = true;
            }
            _layer.Visibility = Visibility.Visible;
            Render();
        }

        private void OnRendering(object? sender, EventArgs args) {
            Render();
        }

        private void Render() {
            var distance = PositiveModulo(Clock.Elapsed.TotalSeconds * Speed - _pathOffset, Spacing);
            var arrowIndex = 0;
            while (distance <= _length) {
                var arrow = GetArrow(arrowIndex++);
                SetPosition(arrow, distance);
                arrow.Visibility = Visibility.Visible;
                distance += Spacing;
            }
            while (arrowIndex < _layer.Children.Count) {
                _layer.Children[arrowIndex++].Visibility = Visibility.Collapsed;
            }
        }

        private Polygon GetArrow(int index) {
            if (index < _layer.Children.Count) {
                return (Polygon)_layer.Children[index];
            }

            var arrow = new Polygon() {
                Fill = Brushes.Black,
                IsHitTestVisible = false,
                Points = [
                    new Point(HalfLength, 0),
                    new Point(-HalfLength, HalfWidth),
                    new Point(-HalfLength, -HalfWidth),
                ],
                RenderTransform = new MatrixTransform(Matrix.Identity),
            };
            _layer.Children.Add(arrow);
            return arrow;
        }

        private void SetPosition(Polygon arrow, double distance) {
            var firstLength = GetLength(_points[0], _points[1]);
            var secondLength = GetLength(_points[1], _points[2]);
            Point start;
            Point end;
            double segmentDistance;
            if ((firstLength > 0 && distance <= firstLength) || secondLength == 0) {
                start = _points[0];
                end = _points[1];
                segmentDistance = distance;
            } else {
                start = _points[1];
                end = _points[2];
                segmentDistance = distance - firstLength;
            }

            var segmentLength = GetLength(start, end);
            if (segmentLength == 0) return;
            var ux = (end.X - start.X) / segmentLength;
            var uy = (end.Y - start.Y) / segmentLength;
            var x = start.X + ux * segmentDistance;
            var y = start.Y + uy * segmentDistance;
            ((MatrixTransform)arrow.RenderTransform).Matrix = new Matrix(
                ux, uy, -uy, ux, x, y);
        }

        private void Stop() {
            if (_isActive) {
                CompositionTarget.Rendering -= OnRendering;
                _isActive = false;
            }
            _layer.Visibility = Visibility.Collapsed;
        }

        private static double PositiveModulo(double value, double modulus) {
            return (value % modulus + modulus) % modulus;
        }

        private static double GetLength(Point start, Point end) {
            var dx = end.X - start.X;
            var dy = end.Y - start.Y;
            return Math.Sqrt(dx * dx + dy * dy);
        }
    }
}