"OnPaint" flickering on text lines. can it be avoided somehow? [source code included]

[jari_stockholm]

Hi There
Anyone got a idea how to get rid of the flickering?

Yes, complete source code is pasted also.
copy and paste the code and RUN it.
now move the mouse up and down...

Option Explicit On

Public Class Form1
    Dim iLine As Integer
    Dim iTab As Integer

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

        Dim myGraphics As Graphics = MyBase.CreateGraphics()
        Dim myPen As New Pen(Color.FromArgb(45, 45, 45))
        Dim myBrush As New SolidBrush(Color.FromArgb(230, 230, 230))
        Dim myBrush2 As New SolidBrush(Color.FromArgb(80, 80, 80))
        Dim g As Graphics = e.Graphics

         [1] Draw the rectangle behind text line
        myGraphics.FillRectangle(myBrush, iTab, iLine, 300, 20)

         [2] Draw 20 lines with some text
        For i = 0 To 20
            g.DrawString("Textline_" & (i), New Font("Verdena", 12), myBrush2, iTab, i * 20)
        Next i

        MyBase.OnPaint(e)
    End Sub

    Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove

         iline is used to -> Dont update screen while mouse at same line as last time
         my idea to avoid unnessesary screen updates

        Select Case e.Y
            Case 0 To 19 And iLine <> 0
                iLine = 0
                Me.Invalidate()
            Case 20 To 39 And iLine <> 20
                iLine = 20
                Me.Invalidate()
            Case 40 To 59 And iLine <> 40
                iLine = 40
                Me.Invalidate()
            Case 60 To 79 And iLine <> 60
                iLine = 60
                Me.Invalidate()
            Case 80 To 99 And iLine <> 80
                iLine = 80
                Me.Invalidate()
            Case 100 To 119 And iLine <> 100
                iLine = 100
                Me.Invalidate()
            Case 120 To 139 And iLine <> 120
                iLine = 120
                Me.Invalidate()
            Case 140 To 159 And iLine <> 140
                iLine = 140
                Me.Invalidate()
            Case 160 To 179 And iLine <> 160
                iLine = 160
                Me.Invalidate()
            Case 180 To 199 And iLine <> 180
                iLine = 180
                Me.Invalidate()
        End Select

    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub

End Class

 

[PlausiblyDamp]

Re: "OnPaint" flickering on text lines. can it be avoided somehow? [source code inclu

Try adding

    Public Sub New()

         This call is required by the Windows Form Designer.
        InitializeComponent()

         Add any initialization after the InitializeComponent() call.
        DoubleBuffered = True
    End Sub

to the form and see if that helps. Also is there a reason you are doing the call to base.CreateGraphics in the OnPaint as you could just use e.Graphics for all the drawing.

 

[jari_stockholm]

Re: "OnPaint" flickering on text lines & rectangle. [sollution included]

well... seems flickerfree now.
no flickering text and a flickerfree progressbar added
just add a timer and run code. hope it helps someone out there.

Option Explicit On
Imports System.Drawing.Drawing2D

Public Class Form1
    Dim iWidth As Integer
    Dim iLine As Integer

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Timer1.Interval = 10
        Timer1.Enabled = True
        Me.DoubleBuffered = True
        iWidth = 1
        iLine = 20
    End Sub

    Protected Overrides Sub OnPaint(ByVal pe As PaintEventArgs)
        Dim g As Graphics = pe.Graphics
        Dim fnt As New Font("Verdana", 10)
        Dim rect As New Rectangle(20, iLine, iWidth, 20)
        Dim lBrush As New LinearGradientBrush(rect, Color.Red, Color.Yellow, LinearGradientMode.BackwardDiagonal)

        g.FillRectangle(lBrush, rect)
        For i = 1 To 20
            g.DrawString("GDI+ World", fnt, New SolidBrush(Color.Red), 20, i * 20)
        Next i
    End Sub

    Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
        Select Case e.Y
            Case 0 To 19 And iLine <> 0
                iLine = 0
            Case 20 To 39 And iLine <> 20
                iLine = 20
            Case 40 To 59 And iLine <> 40
                iLine = 40
            Case 60 To 79 And iLine <> 60
                iLine = 60
            Case 80 To 99 And iLine <> 80
                iLine = 80
            Case 100 To 119 And iLine <> 100
                iLine = 100
            Case 120 To 139 And iLine <> 120
                iLine = 120
            Case 140 To 159 And iLine <> 140
                iLine = 140
            Case 160 To 179 And iLine <> 160
                iLine = 160
            Case 180 To 199 And iLine <> 180
                iLine = 180
        End Select
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        iWidth = iWidth + 1
        Me.Text = iWidth
        If iWidth = 400 Then iWidth = 1
        Me.Refresh()
    End Sub
End Class