Panel flicker

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  • Sarika
    #1

    Panel flicker

    I migrated a VB6.0 application to VB.NET. This app has a drawing area, which
    is a panel. The user can drag and drop several objects on this drawing area
    and can also draw lines, boxes etc. The app is sufferring from the problem of
    flicker.

    On reading several posts on this forum and others I decided to enable double
    buffering for my panel. However the drawing area appears blank. I can briefly
    see the objects when adding new objects on the drawing area.

    I have a context menu associated w/ the panel. On clicking the Show option
    in the context menu, the drawing appears, however on resizing the form or
    adding a new object to the drawing area, the screen becomes blank again.

    Any idea as to what I am missing here?

    Posting some code snippets below, if that will help.

    Thanks in advance for your help.


    Code:

    'This class defines an object which is a specialized panel, which eliminates
    'the flickering effect when used as a drawing pad

    Public Class CBufferedPanel
    Inherits Panel

    Public Sub New()
    MyBase.New()

    SetStyle(Contro lStyles.AllPain tingInWmPaint Or _
    ControlStyles.D oubleBuffer Or _
    ControlStyles.R esizeRedraw Or _
    ControlStyles.U serPaint, _
    True)

    UpdateStyles()
    End Sub
    End Class

    'In the form that has the panel, I define picSegment of type CBuffered class
    and instantiate it
    Public Class DrawingArea
    Inherits System.Windows. Forms.Form

    Private Sub picSegment_Pain t(ByVal Sender As Object, ByVal pea As
    PaintEventArgs) _
    Handles picSegment.Pain t

    'Paint method calls the draw routine
    DrawAll(picSegm ent, True)
    End Sub

    End Class
    Tags: None
    • Ken Tucker [MVP]
      #2
      Re: Panel flicker

      Hi,

      You need to use the graphics object passed to you in paint event to
      draw on the panel. I dont see you passing it to your drawall procedure.
      The graphics object is passed in pea.

      Ken
      -----------------
      "Sarika" <Sarika@discuss ions.microsoft. com> wrote in message
      news:4D6945F6-C377-4E43-9799-2374E7838CBB@mi crosoft.com...[color=blue]
      > I migrated a VB6.0 application to VB.NET. This app has a drawing area,
      > which
      > is a panel. The user can drag and drop several objects on this drawing
      > area
      > and can also draw lines, boxes etc. The app is sufferring from the problem
      > of
      > flicker.
      >
      > On reading several posts on this forum and others I decided to enable
      > double
      > buffering for my panel. However the drawing area appears blank. I can
      > briefly
      > see the objects when adding new objects on the drawing area.
      >
      > I have a context menu associated w/ the panel. On clicking the Show option
      > in the context menu, the drawing appears, however on resizing the form or
      > adding a new object to the drawing area, the screen becomes blank again.
      >
      > Any idea as to what I am missing here?
      >
      > Posting some code snippets below, if that will help.
      >
      > Thanks in advance for your help.
      >
      >
      > Code:
      >
      > 'This class defines an object which is a specialized panel, which
      > eliminates
      > 'the flickering effect when used as a drawing pad
      >
      > Public Class CBufferedPanel
      > Inherits Panel
      >
      > Public Sub New()
      > MyBase.New()
      >
      > SetStyle(Contro lStyles.AllPain tingInWmPaint Or _
      > ControlStyles.D oubleBuffer Or _
      > ControlStyles.R esizeRedraw Or _
      > ControlStyles.U serPaint, _
      > True)
      >
      > UpdateStyles()
      > End Sub
      > End Class
      >
      > 'In the form that has the panel, I define picSegment of type CBuffered
      > class
      > and instantiate it
      > Public Class DrawingArea
      > Inherits System.Windows. Forms.Form
      >
      > Private Sub picSegment_Pain t(ByVal Sender As Object, ByVal pea As
      > PaintEventArgs) _
      > Handles picSegment.Pain t
      >
      > 'Paint method calls the draw routine
      > DrawAll(picSegm ent, True)
      > End Sub
      >
      > End Class[/color]


        Comment

        • Sarika
          #3
          Re: Panel flicker

          Hi Ken,

          Thanks for your response. I pass the panel "picSegment " to the DrawAll
          method and create a graphics object in the DrawAll method. The various
          objects on the screen are drawn by their individual methods.

          I am pasting the code snippet for your ref.

          Thanks in advance for your help.

          ///
          Public Sub DrawAll(ByVal Pic As Object, Optional ByVal Clear As
          Boolean = True, _
          Optional ByVal watermark As Boolean = False)

          Dim wm As String
          Dim g As Graphics

          g = Pic.CreateGraph ics

          If Clear Then g.Clear(Pic.Bac kColor)

          If watermark = True Then
          wm = "Copyright "
          Pic.Font = New Font("Arial", 28)

          CurrentX = (Pic.ClientRect angle.Width - g.MeasureString (wm,
          Pic.Font).Width ) / 2
          CurrentY = (Pic.ClientRect angle.Height - g.MeasureString (wm,
          Pic.Font).Heigh t) / 2
          g.DrawString(wm , Pic.Font, WmarkBrush, CurrentX, CurrentY)

          Pic.Font = New Font("Arial", 8)
          End If

          For Each child In Items
          child.Paint(Pic )
          Next child

          For Each child In Links
          child.Paint(Pic )
          Next child

          For Each child In Texts
          child.Paint(Pic )
          Next child

          For Each child In Lines
          child.Paint(Pic )
          Next child

          For Each child In Boxes
          child.Paint(Pic )
          Next child

          g.Dispose()
          WmarkBrush.Disp ose()
          End Sub
          \\\

            Comment

            • Ronchese
              #4
              Re: Panel flicker

              You are calling your DrawAll method in the OnPaint() event already?

              A suggestion to improve your painting is write the image in a new bitmap,
              and later draw it directly to control's graphic object.

              For sample:



              Private Sub MyGrid_Paint(By Val sender As Object, ByVal e As
              System.Windows. Forms.PaintEven tArgs) Handles MyBase.Paint

              Dim g As System.Drawing. Graphics

              (...)

              Dim bmp As New Bitmap(rectClie nt.Width, rectClient.Heig ht,
              Imaging.PixelFo rmat.Format32bp pArgb)
              g = Graphics.FromIm age(bmp)

              (...) 'draw everything in the g object created above

              'transfer to control's graphics object
              e.Graphics.Draw Image(bmp, New Point(0, 0))

              'release memory
              g.Dispose()

              End sub



              []s
              Cesar



              "Sarika" <Sarika@discuss ions.microsoft. com> escreveu na mensagem
              news:10FF2404-D65E-4D6E-857B-5F3ACEB943DF@mi crosoft.com...
              Hi Ken,

              Thanks for your response. I pass the panel "picSegment " to the DrawAll
              method and create a graphics object in the DrawAll method. The various
              objects on the screen are drawn by their individual methods.

              I am pasting the code snippet for your ref.

              Thanks in advance for your help.

              ///
              Public Sub DrawAll(ByVal Pic As Object, Optional ByVal Clear As
              Boolean = True, _
              Optional ByVal watermark As Boolean = False)

              Dim wm As String
              Dim g As Graphics

              g = Pic.CreateGraph ics

              If Clear Then g.Clear(Pic.Bac kColor)

              If watermark = True Then
              wm = "Copyright "
              Pic.Font = New Font("Arial", 28)

              CurrentX = (Pic.ClientRect angle.Width - g.MeasureString (wm,
              Pic.Font).Width ) / 2
              CurrentY = (Pic.ClientRect angle.Height - g.MeasureString (wm,
              Pic.Font).Heigh t) / 2
              g.DrawString(wm , Pic.Font, WmarkBrush, CurrentX, CurrentY)

              Pic.Font = New Font("Arial", 8)
              End If

              For Each child In Items
              child.Paint(Pic )
              Next child

              For Each child In Links
              child.Paint(Pic )
              Next child

              For Each child In Texts
              child.Paint(Pic )
              Next child

              For Each child In Lines
              child.Paint(Pic )
              Next child

              For Each child In Boxes
              child.Paint(Pic )
              Next child

              g.Dispose()
              WmarkBrush.Disp ose()
              End Sub
              \\\


                Comment

                • Sarika
                  #5
                  Re: Panel flicker

                  Thanks all for your inputs.

                  As mentioned in <a href="http://www.bobpowell.n et/creategraphics. htm">GDI
                  Info</a> and also by you, I improvised my Paint routine. I was unnecessarily
                  creating a Graphics object instead of utilizing the object provided by the
                  PaintEventArgs argument. After optimizing the routine I enabled double
                  buffering on the Panel and yohoo! the flicker was gone...

                  Thanks!

                    Comment

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