3rdpartylibs/fastreports.wpf/FastReport.Forms.WPF/Controls/ShadowControl.cs

using System.Windows.Media;

namespace System.Windows.Forms
{
    public class ShadowControl : Control
    {
        private Shadow shadow { get; }

        private System.Drawing.Color color;
        public Drawing.Color Color 
        { 
            get => color;
            set
            {
                color = value;
                UpdateControl();
            }
        }

        private int depth;
        public int Depth
        {
            get => depth;
            set
            {
                depth = value;
                UpdateControl();
            }
        }

        private DockStyle dock;
        public override DockStyle Dock 
        { 
            get => dock; 
            set
            {
                dock = value;
                UpdateControl();
            }
        }

        private void UpdateControl()
        {
            int angle = dock switch
            {
                DockStyle.Left => 180,
                DockStyle.Bottom => 90,
                DockStyle.Top => 270,
                _ => 0,
            };

            bool vertical = dock == DockStyle.Left || dock == DockStyle.Right;
            if (vertical)
                shadow.Width = depth;
            else
                shadow.Height = depth;

            shadow.Background = new LinearGradientBrush(Helper.GetColor(Color), Helper.GetColor(System.Drawing.Color.FromArgb(0, Color)), angle);
            shadow.InvalidateVisual();
        }

        public ShadowControl()
        {
            shadow = new Shadow() { IsHitTestVisible = false };
            SetControl(shadow);
            depth = 3;
            Dock = DockStyle.Bottom;
        }

        private class Shadow : System.Windows.Controls.Control
        {
            protected override void OnRender(DrawingContext drawingContext)
            {
                base.OnRender(drawingContext);
                drawingContext.PushOpacity(0.7);
                drawingContext.DrawRectangle(Background, null, new Rect(0, 0, ActualWidth, ActualHeight));
            }
        }
    }

    public static class ShadowControlExtensions
    {
        public static ShadowControl SetShadow(this Control control, DockStyle dock)
        {
            var shadow = new ShadowControl() { Dock = dock };
            var shCtl = shadow.control;
            var ctl = control.control;
            (ctl.Parent as System.Windows.Controls.Panel)?.Children.Add(shadow.control);

            ctl.LayoutUpdated += (s, e) =>
            {
                shCtl.Visibility = ctl.Visibility;
                switch (shadow.Dock)
                {
                    case DockStyle.Left:
                        shCtl.Margin = new Thickness(ctl.Margin.Left - shadow.Depth, ctl.Margin.Top, 0, 0);
                        shCtl.Height = ctl.ActualHeight;
                        break;
                    case DockStyle.Right:
                        shCtl.Margin = new Thickness(ctl.Margin.Left + ctl.ActualWidth, ctl.Margin.Top, 0, 0);
                        shCtl.Height = ctl.ActualHeight;
                        break;
                    case DockStyle.Top:
                        shCtl.Margin = new Thickness(ctl.Margin.Left, ctl.Margin.Top - shadow.Depth, 0, 0);
                        shCtl.Width = ctl.ActualWidth;
                        break;
                    case DockStyle.Bottom:
                        shCtl.Margin = new Thickness(ctl.Margin.Left, ctl.Margin.Top + ctl.ActualHeight, 0, 0);
                        shCtl.Width = ctl.ActualWidth;
                        break;
                }
            };

            return shadow;
        }
    }
}