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Quellcode

using System;
using System.Timers;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Media;
using System.Windows.Input;

namespace RPG.Editor.Framework {
    public class AutoScrollViewer : ScrollViewer {
        readonly VisualCollection _visuals;
        const double ScrollBaseSize = 2.5,
            InvisibleCursorRadius = 12,
            FourWayCursorRadius = 60;

        Point _scrollBasePosition;
        Vector _vector;
        readonly Timer _ht,
            _vt;

        readonly DrawingVisual _scrollBase;

        public AutoScrollViewer()
            : base() {
            _visuals = new VisualCollection(this);

            _ht = new Timer {Interval = 80};
            _ht.Elapsed += new ElapsedEventHandler(ScrollTickX);

            _vt = new Timer {Interval = 80};
            _vt.Elapsed += new ElapsedEventHandler(ScrollTickY);

            _scrollBase = new DrawingVisual();
            using (DrawingContext dc = _scrollBase.RenderOpen()) {
                dc.DrawEllipse(Brushes.Black, new Pen(Brushes.White, 1), new Point(ScrollBaseSize, ScrollBaseSize), ScrollBaseSize, ScrollBaseSize);
            }
            _scrollBase.Opacity = 0;
            _visuals.Add(_scrollBase);
        }

        private Timer HorizontalTimer {
            get { return _ht; }
        }

        private Timer VerticalTimer {
            get {  return _vt; }
        }

        private DrawingVisual ScrollBase {
            get { return _scrollBase; }
        }

        protected override Visual GetVisualChild(int index) {
            if(index >= base.VisualChildrenCount)
                return _visuals[index - base.VisualChildrenCount];
            return base.GetVisualChild(index);
        }

        protected override int VisualChildrenCount {
            get { return _visuals.Count + base.VisualChildrenCount; }
        }

        protected override void OnMouseDown(MouseButtonEventArgs e) {
            base.OnMouseDown(e);
            if (e.MouseDevice.MiddleButton == MouseButtonState.Pressed) {
                _scrollBasePosition = e.MouseDevice.GetPosition(this);

                ScrollBase.Opacity = 1;
                ScrollBase.Offset = new Vector(_scrollBasePosition.X, _scrollBasePosition.Y);
                Cursor = Cursors.None;

                if (HorizontalScrollBarVisibility == ScrollBarVisibility.Visible)
                    HorizontalTimer.Enabled = true;
                if (VerticalScrollBarVisibility == ScrollBarVisibility.Visible)
                    VerticalTimer.Enabled = true;
            }
        }
        protected override void OnMouseUp(MouseButtonEventArgs e) {
            base.OnMouseUp(e);
            if (e.MouseDevice.MiddleButton == MouseButtonState.Released) {
                ScrollBase.Opacity = 0;
                HorizontalTimer.Stop();
                VerticalTimer.Stop();
                Cursor = Cursors.Arrow;
            }
        }
        protected override void OnMouseMove(MouseEventArgs e) {
            base.OnMouseMove(e);
            if (e.MiddleButton == MouseButtonState.Pressed) {
                _vector = _scrollBasePosition - e.MouseDevice.GetPosition(this);

                if (_vector.Length < InvisibleCursorRadius) {
                    Cursor = Cursors.None;
                    return;
                }

                if (HorizontalTimer.Enabled && VerticalTimer.Enabled) {
                    double absX = Math.Abs(_vector.X),
                        absY = Math.Abs(_vector.Y);
                    if (_vector.X > 0 && absX > absY) Cursor = Cursors.ScrollW;
                    if (_vector.X < 0 && absX > absY) Cursor = Cursors.ScrollE;
                    if (_vector.Y > 0 && absY > absX) Cursor = Cursors.ScrollN;
                    if (_vector.Y < 0 && absY > absX) Cursor = Cursors.ScrollS;

                    if (_vector.Length > FourWayCursorRadius && Math.Abs(absX - absY) < _vector.Length / 2 && Math.Abs(absY - absX) < _vector.Length / 2) {
                        if (_vector.X > 0 && _vector.Y > 0) Cursor = Cursors.ScrollNW;
                        if (_vector.X < 0 && _vector.Y > 0) Cursor = Cursors.ScrollNE;
                        if (_vector.X > 0 && _vector.Y < 0) Cursor = Cursors.ScrollSW;
                        if (_vector.X < 0 && _vector.Y < 0) Cursor = Cursors.ScrollSE;
                    }
                } else {
                    if (HorizontalTimer.Enabled) {
                        if (_vector.X > 0) Cursor = Cursors.ScrollW;
                        if (_vector.X < 0) Cursor = Cursors.ScrollE;
                    }
                    if (VerticalTimer.Enabled) {
                        if (_vector.Y > 0) Cursor = Cursors.ScrollN;
                        if (_vector.Y < 0) Cursor = Cursors.ScrollS;
                    }
                }
            }
        }
        void ScrollTickX(object sender, ElapsedEventArgs e) {
            Dispatcher.Invoke((Action)(() => ScrollToHorizontalOffset(HorizontalOffset - _vector.X)));
        }
        void ScrollTickY(object sender, ElapsedEventArgs e) {
            Dispatcher.Invoke((Action)(() => ScrollToVerticalOffset(VerticalOffset - _vector.Y)));
        }
    }
}