How to: Select Ink from a Custom Control

Article
02/06/2023

By adding an IncrementalLassoHitTester to your custom control, you can enable your control so that a user can select ink with a lasso tool, similar to the way the InkCanvas selects ink with a lasso.

This example assumes you are familiar with creating an ink-enabled custom control. To create a custom control that accepts ink input, see Creating an Ink Input Control.

Example

When the user draws a lasso, the IncrementalLassoHitTester predicts which strokes will be within the lasso path's boundaries after the user completes the lasso. Strokes that are determined to be within the lasso path's boundaries can be thought of as being selected. Selected strokes can also become unselected. For example, if the user reverses direction while drawing the lasso, the IncrementalLassoHitTester may unselect some strokes.

The IncrementalLassoHitTester raises the SelectionChanged event, which enables your custom control to respond while the user is drawing the lasso. For example, you can change the appearance of strokes as the user selects and unselects them.

Managing the Ink Mode

It is helpful to the user if the lasso appears differently than the ink on your control. To accomplish this, your custom control must keep track of whether the user is writing or selecting ink. The easiest way to do this is to declare an enumeration with two values: one to indicate that the user is writing ink and one to indicate that the user is selecting ink.

// Enum that keeps track of whether StrokeCollectionDemo is in ink mode
// or select mode.
public enum InkMode
{
    Ink, Select
}

' Enum that keeps track of whether StrokeCollectionDemo is in ink mode 
' or select mode.
Public Enum InkMode
    Ink
    [Select]
End Enum 'InkMode

Next, add two DrawingAttributes to the class: one to use when the user writes ink, one to use when the user selects ink. In the constructor, initialize the DrawingAttributes and attach both AttributeChanged events to the same event handler. Then set the DrawingAttributes property of the DynamicRenderer to the ink DrawingAttributes.

DrawingAttributes inkDA;
DrawingAttributes selectDA;

Private inkDA As DrawingAttributes
Private selectDA As DrawingAttributes

// In the constructor.
// Selection drawing attributes use dark gray ink.
selectDA = new DrawingAttributes();
selectDA.Color = Colors.DarkGray;

// ink drawing attributes use default attributes
inkDA = new DrawingAttributes();
inkDA.Width = 5;
inkDA.Height = 5;

inkDA.AttributeChanged += new PropertyDataChangedEventHandler(DrawingAttributesChanged);
selectDA.AttributeChanged += new PropertyDataChangedEventHandler(DrawingAttributesChanged);

' In the constructor.
' Selection drawing attributes use dark gray ink.
selectDA = New DrawingAttributes()
selectDA.Color = Colors.DarkGray

' ink drawing attributes use default attributes
inkDA = New DrawingAttributes()
inkDA.Width = 5
inkDA.Height = 5

AddHandler inkDA.AttributeChanged, _
           AddressOf DrawingAttributesChanged

AddHandler selectDA.AttributeChanged, _
           AddressOf DrawingAttributesChanged

Add a property that exposes the selection mode. When the user changes the selection mode, set the DrawingAttributes property of the DynamicRenderer to the appropriate DrawingAttributes object and then reattach the RootVisual Property to the InkPresenter.

// Property to indicate whether the user is inputting or
// selecting ink.
public InkMode Mode
{
    get
    {
        return mode;
    }

    set
    {
        mode = value;

        // Set the DrawingAttributes of the DynamicRenderer
        if (mode == InkMode.Ink)
        {
            renderer.DrawingAttributes = inkDA;
        }
        else
        {
            renderer.DrawingAttributes = selectDA;
        }

        // Reattach the visual of the DynamicRenderer to the InkPresenter.
        presenter.DetachVisuals(renderer.RootVisual);
        presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes);
    }
}

' Property to indicate whether the user is inputting or
' selecting ink.  
Public Property Mode() As InkMode
    Get
        Return Mode
    End Get

    Set(ByVal value As InkMode)
        modeState = value

        ' Set the DrawingAttributes of the DynamicRenderer
        If modeState = InkMode.Ink Then
            renderer.DrawingAttributes = inkDA
        Else
            renderer.DrawingAttributes = selectDA
        End If

        ' Reattach the visual of the DynamicRenderer to the InkPresenter.
        presenter.DetachVisuals(renderer.RootVisual)
        presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes)
    End Set
End Property

Expose the DrawingAttributes as properties so applications can determine the appearance of the ink strokes and selection strokes.

// Property to allow the user to change the pen's DrawingAttributes.
public DrawingAttributes InkDrawingAttributes
{
    get
    {
        return inkDA;
    }
}

// Property to allow the user to change the Selector'newStroke DrawingAttributes.
public DrawingAttributes SelectDrawingAttributes
{
    get
    {
        return selectDA;
    }
}

' Property to allow the user to change the pen's DrawingAttributes.
Public ReadOnly Property InkDrawingAttributes() As DrawingAttributes
    Get
        Return inkDA
    End Get
End Property

' Property to allow the user to change the Selector'newStroke DrawingAttributes.
Public ReadOnly Property SelectDrawingAttributes() As DrawingAttributes
    Get
        Return selectDA
    End Get
End Property

When a property of a DrawingAttributes object changes, the RootVisual must be reattached to the InkPresenter. In the event handler for the AttributeChanged event, reattach the RootVisual to the InkPresenter.

void DrawingAttributesChanged(object sender, PropertyDataChangedEventArgs e)
{
    // Reattach the visual of the DynamicRenderer to the InkPresenter
    // whenever the DrawingAttributes change.
    presenter.DetachVisuals(renderer.RootVisual);
    presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes);
}

Private Sub DrawingAttributesChanged(ByVal sender As Object, _
                             ByVal e As PropertyDataChangedEventArgs)

    ' Reattach the visual of the DynamicRenderer to the InkPresenter 
    ' whenever the DrawingAttributes change.
    presenter.DetachVisuals(renderer.RootVisual)
    presenter.AttachVisuals(renderer.RootVisual, _
                            renderer.DrawingAttributes)

End Sub

Using the IncrementalLassoHitTester

Create and initialize a StrokeCollection that contains the selected strokes.

// StylusPointCollection that collects the stylus points from the stylus events.
StylusPointCollection stylusPoints;

' StylusPointCollection that collects the stylus points from the stylus events.
Private stylusPoints As StylusPointCollection

When the user starts to draw a stroke, either ink or the lasso, unselect any selected strokes. Then, if the user is drawing a lasso, create an IncrementalLassoHitTester by calling GetIncrementalLassoHitTester, subscribe to the SelectionChanged event, and call AddPoints. This code can be a separate method and called from the OnStylusDown and OnMouseDown methods.

private void InitializeHitTester(StylusPointCollection collectedPoints)
{
    // Deselect any selected strokes.
    foreach (Stroke selectedStroke in selectedStrokes)
    {
        selectedStroke.DrawingAttributes.Color = inkDA.Color;
    }
    selectedStrokes.Clear();

    if (mode == InkMode.Select)
    {
        // Remove the previously drawn lasso, if it exists.
        if (lassoPath != null)
        {
            presenter.Strokes.Remove(lassoPath);
            lassoPath = null;
        }

        selectionTester =
            presenter.Strokes.GetIncrementalLassoHitTester(80);
        selectionTester.SelectionChanged +=
            new LassoSelectionChangedEventHandler(selectionTester_SelectionChanged);
        selectionTester.AddPoints(collectedPoints);
    }
}

Private Sub InitializeHitTester(ByVal collectedPoints As StylusPointCollection)

    ' Deselect any selected strokes.
    Dim selectedStroke As Stroke
    For Each selectedStroke In selectedStrokes
        selectedStroke.DrawingAttributes.Color = inkDA.Color
    Next selectedStroke
    selectedStrokes.Clear()

    If modeState = InkMode.Select Then
        ' Remove the previously drawn lasso, if it exists.
        If Not (lassoPath Is Nothing) Then
            presenter.Strokes.Remove(lassoPath)
            lassoPath = Nothing
        End If

        selectionTester = presenter.Strokes.GetIncrementalLassoHitTester(80)
        AddHandler selectionTester.SelectionChanged, AddressOf selectionTester_SelectionChanged
        selectionTester.AddPoints(collectedPoints)
    End If

End Sub

Add the stylus points to the IncrementalLassoHitTester while the user draws the lasso. Call the following method from the OnStylusMove, OnStylusUp, OnMouseMove, and OnMouseLeftButtonUp methods.

private void AddPointsToHitTester(StylusPointCollection collectedPoints)
{

    if (mode == InkMode.Select &&
        selectionTester != null &&
        selectionTester.IsValid)
    {
        // When the control is selecting strokes, add the
        // stylus packetList to selectionTester.
        selectionTester.AddPoints(collectedPoints);
    }
}

Private Sub AddPointsToHitTester(ByVal collectedPoints As StylusPointCollection)

    If modeState = InkMode.Select AndAlso _
       Not selectionTester Is Nothing AndAlso _
       selectionTester.IsValid Then

        ' When the control is selecting strokes, add the
        ' stylus packetList to selectionTester.
        selectionTester.AddPoints(collectedPoints)
    End If

End Sub

Handle the IncrementalLassoHitTester.SelectionChanged event to respond when the user selects and unselects strokes. The LassoSelectionChangedEventArgs class has the SelectedStrokes and DeselectedStrokes properties that get the strokes that were selected and unselected, respectively.

void selectionTester_SelectionChanged(object sender,
    LassoSelectionChangedEventArgs args)
{
    // Change the color of all selected strokes to red.
    foreach (Stroke selectedStroke in args.SelectedStrokes)
    {
        selectedStroke.DrawingAttributes.Color = Colors.Red;
        selectedStrokes.Add(selectedStroke);
    }

    // Change the color of all unselected strokes to
    // their original color.
    foreach (Stroke unselectedStroke in args.DeselectedStrokes)
    {
        unselectedStroke.DrawingAttributes.Color = inkDA.Color;
        selectedStrokes.Remove(unselectedStroke);
    }
}

Private Sub selectionTester_SelectionChanged(ByVal sender As Object, _
                                     ByVal args As LassoSelectionChangedEventArgs)

    ' Change the color of all selected strokes to red.
    Dim selectedStroke As Stroke
    For Each selectedStroke In args.SelectedStrokes
        selectedStroke.DrawingAttributes.Color = Colors.Red
        selectedStrokes.Add(selectedStroke)
    Next selectedStroke

    ' Change the color of all unselected strokes to 
    ' their original color.
    Dim unselectedStroke As Stroke
    For Each unselectedStroke In args.DeselectedStrokes
        unselectedStroke.DrawingAttributes.Color = inkDA.Color
        selectedStrokes.Remove(unselectedStroke)
    Next unselectedStroke

End Sub

When the user finishes drawing the lasso, unsubscribe from the SelectionChanged event and call EndHitTesting.

if (mode == InkMode.Select && lassoPath == null)
{
    // Add the lasso to the InkPresenter and add the packetList
    // to selectionTester.
    lassoPath = newStroke;
    lassoPath.DrawingAttributes = selectDA.Clone();
    presenter.Strokes.Add(lassoPath);
    selectionTester.SelectionChanged -= new LassoSelectionChangedEventHandler
                    (selectionTester_SelectionChanged);
    selectionTester.EndHitTesting();
}

If modeState = InkMode.Select AndAlso lassoPath Is Nothing Then
    ' Add the lasso to the InkPresenter and add the packetList
    ' to selectionTester.
    lassoPath = newStroke
    lassoPath.DrawingAttributes = selectDA.Clone()
    presenter.Strokes.Add(lassoPath)
    RemoveHandler selectionTester.SelectionChanged, _
                  AddressOf selectionTester_SelectionChanged
    selectionTester.EndHitTesting()
End If

Putting it All Together.

The following example is a custom control that enables a user to select ink with a lasso.

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Input;
using System.Windows.Input.StylusPlugIns;
using System.Windows.Ink;

// Enum that keeps track of whether StrokeCollectionDemo is in ink mode
// or select mode.
public enum InkMode
{
    Ink, Select
}

// This control allows the user to input and select ink.  When the
// user selects ink, the lasso remains visible until they erase, or clip
// the selected strokes, or clear the selection.  When the control is
// in selection mode, strokes that are selected turn red.
public class InkSelector : Label
{
    InkMode mode;

    DrawingAttributes inkDA;
    DrawingAttributes selectDA;

    InkPresenter presenter;
    IncrementalLassoHitTester selectionTester;
    StrokeCollection selectedStrokes = new StrokeCollection();

    // StylusPointCollection that collects the stylus points from the stylus events.
    StylusPointCollection stylusPoints;
    // Stroke that represents the lasso.
    Stroke lassoPath;

    DynamicRenderer renderer;

    public InkSelector()
    {
        mode = InkMode.Ink;

        // Use an InkPresenter to display the strokes on the custom control.
        presenter = new InkPresenter();
        this.Content = presenter;

        // In the constructor.
        // Selection drawing attributes use dark gray ink.
        selectDA = new DrawingAttributes();
        selectDA.Color = Colors.DarkGray;

        // ink drawing attributes use default attributes
        inkDA = new DrawingAttributes();
        inkDA.Width = 5;
        inkDA.Height = 5;

        inkDA.AttributeChanged += new PropertyDataChangedEventHandler(DrawingAttributesChanged);
        selectDA.AttributeChanged += new PropertyDataChangedEventHandler(DrawingAttributesChanged);

        // Add a DynmaicRenderer to the control so ink appears
        // to "flow" from the tablet pen.
        renderer = new DynamicRenderer();
        renderer.DrawingAttributes = inkDA;
        this.StylusPlugIns.Add(renderer);
        presenter.AttachVisuals(renderer.RootVisual,
            renderer.DrawingAttributes);
    }

    static InkSelector()
    {
        // Allow ink to be drawn only within the bounds of the control.
        Type owner = typeof(InkSelector);
        ClipToBoundsProperty.OverrideMetadata(owner,
            new FrameworkPropertyMetadata(true));
    }

    // Prepare to collect stylus packets. If Mode is set to Select,
    // get the IncrementalHitTester from the InkPresenter'newStroke
    // StrokeCollection and subscribe to its StrokeHitChanged event.
    protected override void OnStylusDown(StylusDownEventArgs e)
    {
        base.OnStylusDown(e);

        Stylus.Capture(this);

        // Create a new StylusPointCollection using the StylusPointDescription
        // from the stylus points in the StylusDownEventArgs.
        stylusPoints = new StylusPointCollection();
        StylusPointCollection eventPoints = e.GetStylusPoints(this, stylusPoints.Description);

        stylusPoints.Add(eventPoints);

        InitializeHitTester(eventPoints);
    }

    protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
    {
        base.OnMouseLeftButtonDown(e);

        Mouse.Capture(this);

        if (e.StylusDevice != null)
        {
            return;
        }

        Point pt = e.GetPosition(this);

        StylusPointCollection collectedPoints = new StylusPointCollection(new Point[] { pt });

        stylusPoints = new StylusPointCollection();

        stylusPoints.Add(collectedPoints);

        InitializeHitTester(collectedPoints);
    }
    private void InitializeHitTester(StylusPointCollection collectedPoints)
    {
        // Deselect any selected strokes.
        foreach (Stroke selectedStroke in selectedStrokes)
        {
            selectedStroke.DrawingAttributes.Color = inkDA.Color;
        }
        selectedStrokes.Clear();

        if (mode == InkMode.Select)
        {
            // Remove the previously drawn lasso, if it exists.
            if (lassoPath != null)
            {
                presenter.Strokes.Remove(lassoPath);
                lassoPath = null;
            }

            selectionTester =
                presenter.Strokes.GetIncrementalLassoHitTester(80);
            selectionTester.SelectionChanged +=
                new LassoSelectionChangedEventHandler(selectionTester_SelectionChanged);
            selectionTester.AddPoints(collectedPoints);
        }
    }

    // Collect the stylus packets as the stylus moves.
    protected override void OnStylusMove(StylusEventArgs e)
    {
        if (stylusPoints == null)
        {
            return;
        }

        StylusPointCollection collectedPoints = e.GetStylusPoints(this, stylusPoints.Description);
        stylusPoints.Add(collectedPoints);
        AddPointsToHitTester(collectedPoints);
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {

        base.OnMouseMove(e);

        if (e.StylusDevice != null)
        {
            return;
        }

        if (e.LeftButton == MouseButtonState.Released)
        {
            return;
        }

        stylusPoints ??= new StylusPointCollection();

        Point pt = e.GetPosition(this);

        StylusPointCollection collectedPoints = new StylusPointCollection(new Point[] { pt });

        stylusPoints.Add(collectedPoints);

        AddPointsToHitTester(collectedPoints);
    }

    private void AddPointsToHitTester(StylusPointCollection collectedPoints)
    {

        if (mode == InkMode.Select &&
            selectionTester != null &&
            selectionTester.IsValid)
        {
            // When the control is selecting strokes, add the
            // stylus packetList to selectionTester.
            selectionTester.AddPoints(collectedPoints);
        }
    }

    // When the user lifts the stylus, create a Stroke from the
    // collected stylus points and add it to the InkPresenter.
    // When the control is selecting strokes, add the
    // point data to the IncrementalHitTester.
    protected override void OnStylusUp(StylusEventArgs e)
    {
        stylusPoints ??= new StylusPointCollection();
        StylusPointCollection collectedPoints =
            e.GetStylusPoints(this, stylusPoints.Description);

        stylusPoints.Add(collectedPoints);
        AddPointsToHitTester(collectedPoints);
        AddStrokeToPresenter();
        stylusPoints = null;

        Stylus.Capture(null);
    }

    protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
    {

        base.OnMouseLeftButtonUp(e);

        if (e.StylusDevice != null) return;

        if (stylusPoints == null) stylusPoints = new StylusPointCollection();

        Point pt = e.GetPosition(this);

        StylusPointCollection collectedPoints = new StylusPointCollection(new Point[] { pt });

        stylusPoints.Add(collectedPoints);
        AddPointsToHitTester(collectedPoints);
        AddStrokeToPresenter();

        stylusPoints = null;

        Mouse.Capture(null);
    }

    private void AddStrokeToPresenter()
    {
        Stroke newStroke = new Stroke(stylusPoints);

        if (mode == InkMode.Ink)
        {
            // Add the stroke to the InkPresenter.
            newStroke.DrawingAttributes = inkDA.Clone();
            presenter.Strokes.Add(newStroke);
        }

        if (mode == InkMode.Select && lassoPath == null)
        {
            // Add the lasso to the InkPresenter and add the packetList
            // to selectionTester.
            lassoPath = newStroke;
            lassoPath.DrawingAttributes = selectDA.Clone();
            presenter.Strokes.Add(lassoPath);
            selectionTester.SelectionChanged -= new LassoSelectionChangedEventHandler
                            (selectionTester_SelectionChanged);
            selectionTester.EndHitTesting();
        }
    }

    void selectionTester_SelectionChanged(object sender,
        LassoSelectionChangedEventArgs args)
    {
        // Change the color of all selected strokes to red.
        foreach (Stroke selectedStroke in args.SelectedStrokes)
        {
            selectedStroke.DrawingAttributes.Color = Colors.Red;
            selectedStrokes.Add(selectedStroke);
        }

        // Change the color of all unselected strokes to
        // their original color.
        foreach (Stroke unselectedStroke in args.DeselectedStrokes)
        {
            unselectedStroke.DrawingAttributes.Color = inkDA.Color;
            selectedStrokes.Remove(unselectedStroke);
        }
    }

    // Property to indicate whether the user is inputting or
    // selecting ink.
    public InkMode Mode
    {
        get
        {
            return mode;
        }

        set
        {
            mode = value;

            // Set the DrawingAttributes of the DynamicRenderer
            if (mode == InkMode.Ink)
            {
                renderer.DrawingAttributes = inkDA;
            }
            else
            {
                renderer.DrawingAttributes = selectDA;
            }

            // Reattach the visual of the DynamicRenderer to the InkPresenter.
            presenter.DetachVisuals(renderer.RootVisual);
            presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes);
        }
    }
    void DrawingAttributesChanged(object sender, PropertyDataChangedEventArgs e)
    {
        // Reattach the visual of the DynamicRenderer to the InkPresenter
        // whenever the DrawingAttributes change.
        presenter.DetachVisuals(renderer.RootVisual);
        presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes);
    }

    // Property to allow the user to change the pen's DrawingAttributes.
    public DrawingAttributes InkDrawingAttributes
    {
        get
        {
            return inkDA;
        }
    }

    // Property to allow the user to change the Selector'newStroke DrawingAttributes.
    public DrawingAttributes SelectDrawingAttributes
    {
        get
        {
            return selectDA;
        }
    }
}

Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Media
Imports System.Windows.Input
Imports System.Windows.Input.StylusPlugIns
Imports System.Windows.Ink


' Enum that keeps track of whether StrokeCollectionDemo is in ink mode 
' or select mode.
Public Enum InkMode
    Ink
    [Select]
End Enum 'InkMode

' This control allows the user to input and select ink.  When the
' user selects ink, the lasso remains visible until they erase, or clip
' the selected strokes, or clear the selection.  When the control is
' in selection mode, strokes that are selected turn red.
Public Class InkSelector
    Inherits Label

    Private modeState As InkMode

    Private inkDA As DrawingAttributes
    Private selectDA As DrawingAttributes

    Private presenter As InkPresenter
    Private selectionTester As IncrementalLassoHitTester
    Private selectedStrokes As New StrokeCollection()

    ' StylusPointCollection that collects the stylus points from the stylus events.
    Private stylusPoints As StylusPointCollection

    ' Stroke that represents the lasso.
    Private lassoPath As Stroke

    Private renderer As DynamicRenderer


    Public Sub New()
        modeState = InkMode.Ink

        ' Use an InkPresenter to display the strokes on the custom control.
        presenter = New InkPresenter()
        Me.Content = presenter

        ' In the constructor.
        ' Selection drawing attributes use dark gray ink.
        selectDA = New DrawingAttributes()
        selectDA.Color = Colors.DarkGray

        ' ink drawing attributes use default attributes
        inkDA = New DrawingAttributes()
        inkDA.Width = 5
        inkDA.Height = 5

        AddHandler inkDA.AttributeChanged, _
                   AddressOf DrawingAttributesChanged

        AddHandler selectDA.AttributeChanged, _
                   AddressOf DrawingAttributesChanged

        ' Add a DynmaicRenderer to the control so ink appears
        ' to "flow" from the tablet pen.
        renderer = New DynamicRenderer()
        renderer.DrawingAttributes = inkDA
        Me.StylusPlugIns.Add(renderer)
        presenter.AttachVisuals(renderer.RootVisual, _
            renderer.DrawingAttributes)

    End Sub


    Shared Sub New()
        ' Allow ink to be drawn only within the bounds of the control.
        Dim owner As Type = GetType(InkSelector)
        ClipToBoundsProperty.OverrideMetadata(owner, _
            New FrameworkPropertyMetadata(True))

    End Sub

    ' Prepare to collect stylus packets. If Mode is set to Select,  
    ' get the IncrementalHitTester from the InkPresenter'newStroke 
    ' StrokeCollection and subscribe to its StrokeHitChanged event.
    Protected Overrides Sub OnStylusDown(ByVal e As StylusDownEventArgs)
        MyBase.OnStylusDown(e)

        Stylus.Capture(Me)

        ' Create a new StylusPointCollection using the StylusPointDescription
        ' from the stylus points in the StylusDownEventArgs.
        stylusPoints = New StylusPointCollection()
        Dim eventPoints As StylusPointCollection = e.GetStylusPoints(Me, stylusPoints.Description)

        stylusPoints.Add(eventPoints)

        InitializeHitTester(eventPoints)

    End Sub


    Protected Overrides Sub OnMouseLeftButtonDown(ByVal e As MouseButtonEventArgs)
        MyBase.OnMouseLeftButtonDown(e)

        Mouse.Capture(Me)

        If Not (e.StylusDevice Is Nothing) Then
            Return
        End If

        Dim pt As Point = e.GetPosition(Me)

        Dim collectedPoints As New StylusPointCollection(New Point() {pt})

        stylusPoints = New StylusPointCollection()

        stylusPoints.Add(collectedPoints)

        InitializeHitTester(collectedPoints)

    End Sub


    Private Sub InitializeHitTester(ByVal collectedPoints As StylusPointCollection)

        ' Deselect any selected strokes.
        Dim selectedStroke As Stroke
        For Each selectedStroke In selectedStrokes
            selectedStroke.DrawingAttributes.Color = inkDA.Color
        Next selectedStroke
        selectedStrokes.Clear()

        If modeState = InkMode.Select Then
            ' Remove the previously drawn lasso, if it exists.
            If Not (lassoPath Is Nothing) Then
                presenter.Strokes.Remove(lassoPath)
                lassoPath = Nothing
            End If

            selectionTester = presenter.Strokes.GetIncrementalLassoHitTester(80)
            AddHandler selectionTester.SelectionChanged, AddressOf selectionTester_SelectionChanged
            selectionTester.AddPoints(collectedPoints)
        End If

    End Sub

    ' Collect the stylus packets as the stylus moves.
    Protected Overrides Sub OnStylusMove(ByVal e As StylusEventArgs)

        If stylusPoints Is Nothing Then
            Return
        End If

        Dim collectedPoints As StylusPointCollection = e.GetStylusPoints(Me, stylusPoints.Description)
        stylusPoints.Add(collectedPoints)
        AddPointsToHitTester(collectedPoints)

    End Sub


    Protected Overrides Sub OnMouseMove(ByVal e As MouseEventArgs)

        MyBase.OnMouseMove(e)

        If Not (e.StylusDevice Is Nothing) Then
            Return
        End If

        If e.LeftButton = MouseButtonState.Released Then
            Return
        End If

        If stylusPoints Is Nothing Then
            stylusPoints = New StylusPointCollection()
        End If

        Dim pt As Point = e.GetPosition(Me)

        Dim collectedPoints As New StylusPointCollection(New Point() {pt})

        stylusPoints.Add(collectedPoints)

        AddPointsToHitTester(collectedPoints)

    End Sub


    Private Sub AddPointsToHitTester(ByVal collectedPoints As StylusPointCollection)

        If modeState = InkMode.Select AndAlso _
           Not selectionTester Is Nothing AndAlso _
           selectionTester.IsValid Then

            ' When the control is selecting strokes, add the
            ' stylus packetList to selectionTester.
            selectionTester.AddPoints(collectedPoints)
        End If

    End Sub

    ' When the user lifts the stylus, create a Stroke from the
    ' collected stylus points and add it to the InkPresenter.
    ' When the control is selecting strokes, add the
    ' point data to the IncrementalHitTester.
    Protected Overrides Sub OnStylusUp(ByVal e As StylusEventArgs)

        If stylusPoints Is Nothing Then
            stylusPoints = New StylusPointCollection()
        End If

        Dim collectedPoints As StylusPointCollection = _
            e.GetStylusPoints(Me, stylusPoints.Description)

        stylusPoints.Add(collectedPoints)
        AddPointsToHitTester(collectedPoints)
        AddStrokeToPresenter()

        stylusPoints = Nothing

        Stylus.Capture(Nothing)

    End Sub


    Protected Overrides Sub OnMouseLeftButtonUp(ByVal e As MouseButtonEventArgs)

        MyBase.OnMouseLeftButtonUp(e)

        If Not (e.StylusDevice Is Nothing) Then
            Return
        End If
        If stylusPoints Is Nothing Then
            stylusPoints = New StylusPointCollection()
        End If
        Dim pt As Point = e.GetPosition(Me)

        Dim collectedPoints As New StylusPointCollection(New Point() {pt})

        stylusPoints.Add(collectedPoints)
        AddPointsToHitTester(collectedPoints)
        AddStrokeToPresenter()

        stylusPoints = Nothing

        Mouse.Capture(Nothing)

    End Sub


    Private Sub AddStrokeToPresenter()
        Dim newStroke As New Stroke(stylusPoints)

        If modeState = InkMode.Ink Then
            ' Add the stroke to the InkPresenter.
            newStroke.DrawingAttributes = inkDA.Clone()
            presenter.Strokes.Add(newStroke)
        End If

        If modeState = InkMode.Select AndAlso lassoPath Is Nothing Then
            ' Add the lasso to the InkPresenter and add the packetList
            ' to selectionTester.
            lassoPath = newStroke
            lassoPath.DrawingAttributes = selectDA.Clone()
            presenter.Strokes.Add(lassoPath)
            RemoveHandler selectionTester.SelectionChanged, _
                          AddressOf selectionTester_SelectionChanged
            selectionTester.EndHitTesting()
        End If

    End Sub

    Private Sub selectionTester_SelectionChanged(ByVal sender As Object, _
                                         ByVal args As LassoSelectionChangedEventArgs)

        ' Change the color of all selected strokes to red.
        Dim selectedStroke As Stroke
        For Each selectedStroke In args.SelectedStrokes
            selectedStroke.DrawingAttributes.Color = Colors.Red
            selectedStrokes.Add(selectedStroke)
        Next selectedStroke

        ' Change the color of all unselected strokes to 
        ' their original color.
        Dim unselectedStroke As Stroke
        For Each unselectedStroke In args.DeselectedStrokes
            unselectedStroke.DrawingAttributes.Color = inkDA.Color
            selectedStrokes.Remove(unselectedStroke)
        Next unselectedStroke

    End Sub

    ' Property to indicate whether the user is inputting or
    ' selecting ink.  
    Public Property Mode() As InkMode
        Get
            Return Mode
        End Get

        Set(ByVal value As InkMode)
            modeState = value

            ' Set the DrawingAttributes of the DynamicRenderer
            If modeState = InkMode.Ink Then
                renderer.DrawingAttributes = inkDA
            Else
                renderer.DrawingAttributes = selectDA
            End If

            ' Reattach the visual of the DynamicRenderer to the InkPresenter.
            presenter.DetachVisuals(renderer.RootVisual)
            presenter.AttachVisuals(renderer.RootVisual, renderer.DrawingAttributes)
        End Set
    End Property
    Private Sub DrawingAttributesChanged(ByVal sender As Object, _
                                 ByVal e As PropertyDataChangedEventArgs)

        ' Reattach the visual of the DynamicRenderer to the InkPresenter 
        ' whenever the DrawingAttributes change.
        presenter.DetachVisuals(renderer.RootVisual)
        presenter.AttachVisuals(renderer.RootVisual, _
                                renderer.DrawingAttributes)

    End Sub

    ' Property to allow the user to change the pen's DrawingAttributes.
    Public ReadOnly Property InkDrawingAttributes() As DrawingAttributes
        Get
            Return inkDA
        End Get
    End Property

    ' Property to allow the user to change the Selector'newStroke DrawingAttributes.
    Public ReadOnly Property SelectDrawingAttributes() As DrawingAttributes
        Get
            Return selectDA
        End Get
    End Property

End Class

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How to: Select Ink from a Custom Control

Example

Managing the Ink Mode

Using the IncrementalLassoHitTester

Putting it All Together.

See also

Additional resources