How to draw dropshadow effect in a geometry in WPF - wpf

Question

I'm drawing the following Shape in a Canvas.
I would like to highlight it when it's selected by changing its color (the easy part) and drawing an small halo around it:
This is how I did using SASS: http://codepen.io/aaromnido/pen/zKvAwd/
How coud I draw in WPF? Remember that I'm drawing using the Shape's OnRender method.

Answer 1

Set some defaults in constructor.
One of these defaults is Shape.Effect, as it will be animated on MouseEnter event.
Construct VisualStates for Normal , and MouseEnter scenarios.
Change the VisualState of the element using VisualStateManager.GoToElementState() in MouseEnter and MouseLeave event handlers.
You can expose various properties using DPs for customization.
NewShape.cs
using System.Windows.Shapes;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows;
using System.Windows.Media.Effects;
namespace WpfStackOverflow.NewShape
{
public class CNewShape : Shape
{
public CNewShape()
{
// setting the defaults
this.Width = 40;
this.Height = 40;
this.Stroke = new SolidColorBrush() { Color = Colors.Red };
this.StrokeThickness = 5;
this.Effect = new DropShadowEffect() {
Color = Colors.Transparent,
BlurRadius = 1,
Direction = -150,
ShadowDepth = 1
};
// constructing the VisualStates
_constructVisualStates();
// event handlers
this.MouseEnter += CNewShape_MouseEnter;
this.MouseLeave += CNewShape_MouseLeave;
}
#region EventHandlers
void CNewShape_MouseLeave(object sender, System.Windows.Input.MouseEventArgs e)
{
VisualStateManager.GoToElementState(this, "VSNormal", false);
}
void CNewShape_MouseEnter(object sender, System.Windows.Input.MouseEventArgs e)
{
VisualStateManager.GoToElementState(this, "VSMouseEnter", false);
}
#endregion
#region Overrides
// This needs to be implemented as it is abstract in base class
GeometryGroup geo = new GeometryGroup();
protected override Geometry DefiningGeometry
{
get { return geo; }
}
protected override void OnRender(System.Windows.Media.DrawingContext drawingContext)
{
Pen pen = new Pen(this.Stroke, StrokeThickness);
drawingContext.DrawEllipse(Brushes.Transparent, pen, new Point(Width/2, Height/2), 40, 40);
drawingContext.DrawEllipse(Stroke, null, new Point(Width / 2, Height / 2), 30, 30);
base.OnRender(drawingContext);
}
#endregion
#region Helpers
private void _constructVisualStates()
{
VisualStateGroup vsg1 = new VisualStateGroup();
#region VSNormal (Normal Visual State)
VisualState stateVSNormal = new VisualState() { Name = "VSNormal" };
Storyboard sbVSNormal = new Storyboard();
ObjectAnimationUsingKeyFrames oa = new ObjectAnimationUsingKeyFrames();
Storyboard.SetTargetProperty(oa, new PropertyPath("Effect"));
DiscreteObjectKeyFrame dokf = new DiscreteObjectKeyFrame(null);
oa.KeyFrames.Add(dokf);
sbVSNormal.Children.Add(oa);
stateVSNormal.Storyboard = sbVSNormal;
vsg1.States.Add(stateVSNormal);
#endregion
#region VSMouseEnter (MouseEnter Visual State)
VisualState stateVSMouseEnter = new VisualState() { Name = "VSMouseEnter" };
Storyboard sbVSMouseEnter = new Storyboard();
ColorAnimation caStrokeColor = new ColorAnimation();
caStrokeColor.To = (Color)ColorConverter.ConvertFromString("#FF24BCDE");
Storyboard.SetTargetProperty(caStrokeColor, new PropertyPath("(Shape.Stroke).(SolidColorBrush.Color)"));
sbVSMouseEnter.Children.Add(caStrokeColor);
ColorAnimation caEffectColor = new ColorAnimation();
caEffectColor.To = (Color)ColorConverter.ConvertFromString("#FFA4E1F3");
Storyboard.SetTargetProperty(caEffectColor, new PropertyPath("(Shape.Effect).(Color)"));
sbVSMouseEnter.Children.Add(caEffectColor);
DoubleAnimation daBlurRadius = new DoubleAnimation();
daBlurRadius.To = 10;
Storyboard.SetTargetProperty(daBlurRadius, new PropertyPath("(Shape.Effect).(BlurRadius)"));
sbVSMouseEnter.Children.Add(daBlurRadius);
DoubleAnimation daDirection = new DoubleAnimation();
daDirection.To = -190;
Storyboard.SetTargetProperty(daDirection, new PropertyPath("(Shape.Effect).(Direction)"));
sbVSMouseEnter.Children.Add(daDirection);
stateVSMouseEnter.Storyboard = sbVSMouseEnter;
vsg1.States.Add(stateVSMouseEnter);
#endregion
VisualStateManager.GetVisualStateGroups(this).Add(vsg1);
}
#endregion
}
}
Usage
<local:CNewShape Canvas.Left="70" Canvas.Top="52" Stroke="#FF374095" StrokeThickness="10" Width="100" Height="100" />
Output
Quality of the image is bad. On screen actual output looks good.

Answer 2

Whatever your trigger is that your control enters the Highlighted state, in that trigger just set the Effect property. For my test the "trigger" is a property:
public static readonly DependencyProperty ShowShadowProperty =
DependencyProperty.Register ("ShowShadow", typeof (bool), typeof (TestShape), new PropertyMetadata (false, ShowShadowChanged));
public bool ShowShadow
{
get { return (bool)GetValue (ShowShadowProperty); }
set { SetValue (ShowShadowProperty, value); }
}
private static void ShowShadowChanged (DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((TestShape)d).OnShowShadow ();
}
private void OnShowShadow ()
{
if (ShowShadow)
{
Effect = new DropShadowEffect { Direction = 0, ShadowDepth = 20, BlurRadius = 33, Opacity = 1, Color = Colors.Black};
}
else
{
Effect = null;
}
}
Which means you don't need to do anything in OnRender.