No Transparency on Visual Basic PictureBox

问题

I have some picture boxes on Visual Basic Express 2010, and these picture have alpha channels on them, but when the background color is set to transparent, it does not become transparent but becomes the color of the form. I still can't see anything else through the alpha map. What is the problem? I don't only want to see the parent object behind the picture box, but every other object that is underneath it.

回答1:

I have got some code that will create "proper" transparency for a control by drawing every control that's behind it onto it's background.

How to use:

1) Create a custom class. (From the "Add New Item" menu)

2) Give it a name of your choice (ex: TransparentPictureBox)

3) Make it inherit from the original PictureBox.

Public Class TransparentPictureBox
    Inherits PictureBox

End Class

4) Paste this code within the class:

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

The code will override the PictureBox's OnPaintBackground event, thus drawing it's own transparent background.

5) Build your project.

6) Select your component from the ToolBox and add it to your form.

Hope this helps!

Result:

EDIT:

In addition to your comment, start by building your project via the Build > Build <your project name> menu.

Then you can find your custom control at the top of the toolbox under the <your project name> Components category.

来源：https://stackoverflow.com/questions/32431300/no-transparency-on-visual-basic-picturebox

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vb.net

transparency

picturebox