Animation - A class to extract all the frames of an animated image

' This class loads an animated image and gives access to all its internal 
' frames as Bitmap objects
'
' Example:
'    ' load the animation and extract its frames
'    Me.Cursor = Cursors.WaitCursor
'    Dim anim As New Animation("D:\SampleAnimation.gif")
'    Me.Cursor = Cursors.Default
'    ' get a reference to the first and last frame
'    Dim firstFrame As Bitmap = anim.Frame(0)
'    Dim lastFrame As Bitmap = anim.Frame(anim.FrameCount - 1)
'    ' show the frames in two picture boxes
'    PictureBox1.Image = firstFrame
'    PictureBox2.Image = lastFrame

Class Animation
    Implements IDisposable

    Dim m_Img As System.Drawing.Image
    Dim m_Frames As New System.Collections.ArrayList
    Dim m_FrameCount As Integer

    Sub New(ByVal imgPath As String)
        ' load the image
        m_Img = System.Drawing.Image.FromFile(imgPath)

        ' throw an exception and exit if this is not an animated image
        If System.Drawing.ImageAnimator.CanAnimate(m_Img) = False Then
            m_Img.Dispose()
            Throw New ArgumentException("This is not an animated image")
        End If

        ' count the image's frames
        Dim fdl As New Drawing.Imaging.FrameDimension(m_Img.FrameDimensionsList _
            (0))
        m_FrameCount = m_Img.GetFrameCount(fdl)

        ' extract the first frame and start the animation to extract the other 
        ' single frames
        AddCurrentFrame()
        System.Drawing.ImageAnimator.Animate(m_Img, New EventHandler(AddressOf _
            OnFrameChanged))

        Do ' wait until all frames are loaded
        Loop Until Done
    End Sub

    ' Return the total number of frames
    Public ReadOnly Property FrameCount() As Integer
        Get
            Return m_FrameCount
        End Get
    End Property

    ' Return the bitmap of the specified frame, stored in the private ArrayList
    Public ReadOnly Property Frame(ByVal index As Integer) As _
        System.Drawing.Bitmap
        Get
            Return DirectCast(m_Frames(index), System.Drawing.Bitmap)
        End Get
    End Property

    Public Sub Dispose() Implements System.IDisposable.Dispose
        StopAnimate()
    End Sub

    ' ==================== PRIVATE MEMBERS ====================

    ' This method is raised when the current frame changes
    Private Sub OnFrameChanged(ByVal sender As Object, ByVal e As EventArgs)
        ' if the m_Frames array contains FrameCount bitmaps,
        '  it means that the animation run through the end, 
        ' and now it is starting from the beginning again, so stop it
        If Done Then
            StopAnimate()
            Exit Sub
        End If

        ' update the image to the new frame, and save it
        System.Drawing.ImageAnimator.UpdateFrames(m_Img)
        AddCurrentFrame()
    End Sub

    ' Add the current frame to the private ArrayList of bitmaps
    Private Sub AddCurrentFrame()
        ' create a new empty bitmap
        Dim bmp As New System.Drawing.Bitmap(m_Img.Width, m_Img.Height)
        ' retrieve a canvas object that allows to draw on the empty bitmap
        Dim g As System.Drawing.Graphics = System.Drawing.Graphics.FromImage _
            (DirectCast(bmp, System.Drawing.Image))
        ' copy the original image on the canvas, and thus on the new bitmap
        g.DrawImage(m_Img, 0, 0)
        ' add the frame to the array
        m_Frames.Add(bmp)
    End Sub

    ' Return True when the class has extracted all the frames
    Private ReadOnly Property Done() As Boolean
        Get
            Return m_Frames.Count = FrameCount
        End Get
    End Property

    ' Stop the animation and dispose the open image object
    Private Sub StopAnimate()
        System.Drawing.ImageAnimator.StopAnimate(m_Img, _
            New EventHandler(AddressOf OnFrameChanged))
        m_Img.Dispose()
    End Sub
End Class