UserControl/ElementHost Transparent Background

Question

I need a method that sets the background of the ElementHost completely transparent or so that it does not even render in the first place.

Current Structure

In the background I have a PictureBox. Over that there is my UserControl (Which you can Download below). Both the PictureBox and the UserControl have a Width of 150. As you can see in the Picture above, the UserControl is 100% Invisible. In the UserControl is an ElementHost with a Width of 120, within that there is a WPF-Content with a Width of 100.
Everything is Transparent, except the ElementHost1.

My Code

UserControl:

Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
    Get
        Dim cp As CreateParams = MyBase.CreateParams
        cp.ExStyle = &H20
        Return cp
    End Get
End Property

Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
End Sub

Public Overrides Sub Refresh()
    Parent.Invalidate(New Rectangle(Me.Location, Me.Size), True)
End Sub

Public Sub New()
    InitializeComponent()

    Me.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
    Me.BackColor = System.Drawing.Color.Transparent

    ElementHost1.BackColor = System.Drawing.Color.Transparent
    ElementHost1.BackColorTransparent = True
End Sub

I´ve also tried to create a Custom ElementHost:

Public Class TransElementHost
    Inherits ElementHost

    Public Sub TransElementHost()
        Me.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
        Me.BackColorTransparent = True
        'Me.BackColor = System.Drawing.Color.FromArgb(0, 0, 0, 0)
    End Sub

    Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
        Get
            Dim cp As CreateParams = MyBase.CreateParams
            cp.ExStyle = &H20
            Return cp
        End Get
    End Property

    Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
    End Sub

    Public Overrides Sub Refresh()
        Parent.Invalidate(New Rectangle(Me.Location, Me.Size), True)
    End Sub
End Class

My SVGTest-UserControl

Does anybody have an idea?

Answer 1

It's probably not the best fix, but you could try using the ButtonRenderer class. Put this code either in OnPaintBackground or OnPaint.

If Me.BackColor = Color.Transparent Then
    Windows.Forms.ButtonRenderer.DrawParentBackground(e.Graphics, Me.ClientRectangle, Me)
End If

The ButtonRenderer class is used to draw the regular buttons; their border, background, text, image etc.

I used the above code myself to create a custom control with transparent background. (Though I see now that my control inherits from ButtonBase... But the above code is still worth a try).

Answer 2

I know it's been really long since this was active, but if you still need it I've (finally) got a code that will draw controls' backgrounds fully transparent.

Just put this code in the control's code. It overrides the OnPaintBackground event:

Protected Overrides Sub OnPaintBackground(e As System.Windows.Forms.PaintEventArgs)
    MyBase.OnPaintBackground(e)

    If Parent IsNot Nothing Then
        Dim index As Integer = Parent.Controls.GetChildIndex(Me)

        For i As Integer = Parent.Controls.Count - 1 To index + 1 Step -1
            Dim c As Control = Parent.Controls(i)
            If c.Bounds.IntersectsWith(Bounds) AndAlso c.Visible = True Then
                Dim bmp As New Bitmap(c.Width, c.Height, e.Graphics)
                c.DrawToBitmap(bmp, c.ClientRectangle)
                e.Graphics.TranslateTransform(c.Left - Left, c.Top - Top)
                e.Graphics.DrawImageUnscaled(bmp, Point.Empty)
                e.Graphics.TranslateTransform(Left - c.Left, Top - c.Top)
                bmp.Dispose()
            End If
        Next
    End If
End Sub