Dragging Span in ScottPlot

gistfile1.txt

using System;
using ScottPlot;
using ScottPlot.Plottable;
using System.Windows.Forms;

namespace WinFormsApp
{
    public partial class Form1 : Form
    {
        readonly HSpan MySpan;

        bool IsDraggingBody;
        bool IsDraggingLeftEdge;
        bool IsDraggingRightEdge;
        bool IsDragging => IsDraggingBody || IsDraggingLeftEdge || IsDraggingRightEdge;

        double MouseDownX;

        double OriginalSpanX1;
        double OriginalSpanX2;

        public Form1()
        {
            InitializeComponent();

            formsPlot1.Plot.AddSignal(DataGen.Sin(51));
            formsPlot1.Plot.AddSignal(DataGen.Cos(51));
            MySpan = formsPlot1.Plot.AddHorizontalSpan(10, 20);

            // dont use the built-in dragging system
            MySpan.DragEnabled = false;

            // we will create our own dragging actions
            formsPlot1.MouseDown += FormsPlot1_MouseDown;
            formsPlot1.MouseMove += FormsPlot1_MouseMove;
            formsPlot1.MouseUp += FormsPlot1_MouseUp;

            formsPlot1.Refresh();
        }

        private void FormsPlot1_MouseMove(object sender, MouseEventArgs e)
        {
            if (!IsDragging)
                return;

            (double currentX, _) = formsPlot1.GetMouseCoordinates();
            double deltaX = currentX - MouseDownX;

            if (IsDraggingBody)
            {
                MySpan.X1 = OriginalSpanX1 + deltaX;
                MySpan.X2 = OriginalSpanX2 + deltaX;
            }
            else if (IsDraggingLeftEdge)
            {
                MySpan.X1 = OriginalSpanX1 + deltaX;
                MySpan.X2 = OriginalSpanX2 - deltaX;
            }
            else if (IsDraggingRightEdge)
            {
                MySpan.X1 = OriginalSpanX1 - deltaX;
                MySpan.X2 = OriginalSpanX2 + deltaX;
            }

            formsPlot1.Refresh();
        }

        private void FormsPlot1_MouseDown(object sender, MouseEventArgs e)
        {
            (MouseDownX, _) = formsPlot1.GetMouseCoordinates();
            OriginalSpanX1 = MySpan.X1;
            OriginalSpanX2 = MySpan.X2;

            float snapPixels = 5;
            double snapUnits = formsPlot1.Plot.XAxis.Dims.UnitsPerPx * snapPixels;
            double distanceFromLeftEdge = Math.Abs(MouseDownX - MySpan.X1);
            double distanceFromRightEdge = Math.Abs(MouseDownX - MySpan.X2);

            if (distanceFromLeftEdge < snapUnits)
            {
                IsDraggingLeftEdge = true;
            }
            else if (distanceFromRightEdge < snapUnits)
            {
                IsDraggingRightEdge = true;
            }
            else if (MouseDownX >= MySpan.X1 && MouseDownX <= MySpan.X2)
            {
                IsDraggingBody = true;
            }

            if (IsDragging)
                formsPlot1.Configuration.LeftClickDragPan = false;
        }

        private void FormsPlot1_MouseUp(object sender, MouseEventArgs e)
        {
            IsDraggingLeftEdge = false;
            IsDraggingRightEdge = false;
            IsDraggingBody = false;
            formsPlot1.Configuration.LeftClickDragPan = true;
        }
    }
}