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dragging a picturebox over another picturebox.

Posted on 2009-04-06
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Hi,

I am developing a VC++ application and I am trying to make a circle image over a map image to be draggable by mouse. I did this by first creating a picturebox which has its image set to a map and the circle as anothe picturebox  (PNG) which has transparency.

I am setting the first picturebox as the parent of the second picturebox.

I am making the image draggable by using the mousedown events and mouse move events to relocate the circle picturebox to the mouse pointer position.

The problem is, when I do this, the transparent areas of the circle image look messy (flickering) and the circle image is looking strange and not moving smoothly. Am I doing anything wrong? is there a better way to achieve this in VC++ dot net?

Regards,
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Question by:gghaleb
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omegaomega earned 2000 total points
ID: 24089507
Hello, gghaleb,

You might find this smoother if you don't bother with the second PictureBox but instead just draw the circle during the map PictureBox's Paint event.  The snippet shows a simple example.  (It's in VB, but you probably won't have any trouble converting it.)   The MouseMove and MouseUp events simply request repainting of the PictureBox.  The Paint event is then used to draw the circle.

Cheers,
Randy

Public Class Form1
 
    Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
        If (e.Button = Windows.Forms.MouseButtons.Left) Then
            PictureBox1.Invalidate()
        End If
    End Sub
 
    Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseUp
        PictureBox1.Invalidate()
    End Sub
 
    Private Sub PictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
        If (Control.MouseButtons = Windows.Forms.MouseButtons.Left) Then
            Const Radius As Integer = 30
            Dim Centre As Point = PictureBox1.PointToClient(Control.MousePosition)
            Dim CircleFrame As New Rectangle(Centre.X - Radius, Centre.Y - Radius, 2 * Radius, 2 * Radius)
            e.Graphics.DrawEllipse(Pens.Black, CircleFrame)
        End If
    End Sub
 
End Class

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