[RESOLVED] Drawing using BackGroundWorker, I don't see my where I'm wrong.

I'm using drawing routines that are all called by the .Paint Event of my Control.
The calculation of the objects is done in the Routine "SystemTracks_Simulation", also the positional regions where the objects have been and are now get invalidated. This routine is called once for each Frame.

If I use that routine in the GUI thread, everything works as it should. All the different objects are drawn.
However if I use a BackGroundWorker-thread to call the "SystemTracks_Simulation" the respective objects are most of the time not drawn. Only if I do a ReScale (complete Redraw, i.e. Invalidate without Region) the objects are drawn. If the simulation in running the objects are only shown momentarily (which is the problem), if it isn't running the redraw will show all the objects.



Here are the codelines that call the routine either by the BGW or directly.

Code:

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If Not MainForm.BackgroundSystemTracksWorker.IsBusy Then
    MainForm.BackgroundSystemTracksWorker.RunWorkerAsync()
Else
      debug_schreiben("SystemTracks_Sim ausgefallen! ")
End If

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or

Code:

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SystemTracks_Simulation()

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I think I know what may be happening as I had this happen a lot during some games that I made. In my case, one thing that would happen is that the drawing would occur before the physics causing terrible ripping and glitches. The solution in my case was a managed game loop. What does the actual drawing look like and are you using GDI+ or something else?

The (shortened) code that does draw one object (Track)

Code:

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Private Sub TrackDrawing(ByRef e As Graphics, ByRef Pen As Pen, ByRef Brush As SolidBrush, ByVal Track As SystemTrack)
        'Draw a Systemtrack
        Dim j As Integer
        Dim SymbolPos As Point
        Dim Linksymbol As Bitmap
        Dim LinkString As String
        Try
          SymbolPos = Track.PixelPosition
          SymbolPos.X -= 16 'SymbolSize 32*32!!
            SymbolPos.Y -= 16
            Pen.Width = 2
            Pen.LineJoin = Drawing2D.LineJoin.Round
          ' .......
            Linksymbol = CType(Bitmap.FromFile(LinkDirectory & "/" & LinkString), Bitmap)
            Dim TheImage As New Bitmap(Linksymbol, 32, 32)
            TheImage.MakeTransparent()
            Dim ptsArray As Single()() = {New Single() {1, 0, 0, 0, 0}, New Single() {0, 1, 0, 0, 0}, New Single() {0, 0, 1, 0, 0}, New Single() {0, 0, 0, 0.5F, 0}, New Single() {0, 0, 0, 0, 1}}
            Dim clrMatrix As New System.Drawing.Imaging.ColorMatrix(ptsArray)
            Dim imgAttributes As New System.Drawing.Imaging.ImageAttributes
            imgAttributes.SetColorMatrix(clrMatrix, Imaging.ColorMatrixFlag.Default, Imaging.ColorAdjustType.Bitmap)
            e.DrawImage(TheImage, New Rectangle(SymbolPos.X, SymbolPos.Y, TheImage.Width, TheImage.Height), 0, 0, TheImage.Width, TheImage.Height, GraphicsUnit.Pixel, imgAttributes)
          Pen.Width = 1
            Dim Text As String
            If Track.TrackNumber = 0 Then
                Text = "_" & Track.SystemID
            Else
                Text = Track.TrackNumber.ToString
            End If
            Brush.Color = Pen.Color
            e.DrawString(Text, Me.Font, Brush, KursLinie(0).X + 11, KursLinie(0).Y + 11)
        Catch ex As Exception
            ErrLog_schreiben("TrackZeichnen", ex.Message)
        End Try
    End Sub

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My GameLoop looks like that

Code:

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Public Sub TimeControll()
        Static LastSimTime As Integer = Environment.TickCount
        Dim ActualZeit As Integer
        Static CycleCounter As Double
        Try
            ActualZeit = Environment.TickCount
            If LastSimTime + SpeedFactor / FPS <= ActualZeit Then
                Zeitschritte = 1
                If ActualZeit - LastSimTime > SpeedFactor / FPS Then
                    ZeitSchritte = (ActualZeit - LastSimTime) / (SpeedFactor / FPS) 'If the time is lagging, do a bigger step
                End If
                LastSimTime = ActualZeit
                Playtime = ((DateTime.UtcNow.Hour) * 60 + DateTime.UtcNow.Minute) * 60 + DateTime.UtcNow.Second
              Simulation(MainForm, System.EventArgs.Empty)
            End If
            'Application.DoEvents()
            If StartStop = True Then
                'as long as StartStop=True these Routine is calling itself again!
                ExecuteAfterPause(CInt(SpeedFactor / FPS), New MethodInvoker(AddressOf TimeControl))
            End If
        Catch ex As Exception
            ErrLog_schreiben("Zeitkontrolle", ex.Message, StartStop.ToString, ActualZeit.ToString, Playtime.ToString, Mode.ToString)
        End Try
    End Sub

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The code from post #1 are called in "Simulation((MainForm, System.EventArgs.Empty)".
I guess you do recognise your technique, and yes its the Pauser from JMcIlhinney

I'd say that's the issue. You don't really want the Paint routine to be waiting on a background thread, but that means that your paint event may complete before your calculations. The results could be totally bizarre, depending on what you were doing. In the worst case, you could be sharing variables between the paint routine and the foreground, thus setting up a race condition for the painting.

Edit - I already knew the information I asked for :/

Altered post. It's certainly a race condition that's occurring like what Shaggy said. What you'll have to do is rework your code to try and prevent that as much as possible. One thing that I could see what would be causing it is your Try/Catch, that alone is such a resource hog. One other thing which is what I do on my game projects is set it up in this format:

Step 1. Update
Step 2. Draw
Step 3. Render

Each step has a separate thread and one will not perform until the other has finished. Finally my last suggestion is to change your game loop. While the one that I posted using JMcIlhinney's pauser works well, it doesn't work as efficiently as this one here:

Code:

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    Private game_thread As Threading.Thread

    Private Sub Form1_FormClosing(sender As Object, e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        quit = True
    End Sub

    Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load

        game_thread = New Threading.Thread(AddressOf GameLoop)
        game_thread.Start()

    End Sub

    Private quit As Boolean = False
    Private Sub GameLoop()

        Dim s As New Stopwatch
        s.Start()

        'Update
        'Draw
        'Render

        'Loop
        While s.Elapsed <= TimeSpan.FromMilliseconds(16.6)
            Application.DoEvents()
        End While

        Console.WriteLine(s.ElapsedMilliseconds)

        s.Stop()
        If quit = False Then
            game_thread = New Threading.Thread(AddressOf GameLoop)
            game_thread.Start()
        End If
    End Sub

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The reason is because of the nature of the timer, it's just not a high precision instrument where as the stopwatch will be if the computer will allow it to be.

Quote:

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Originally Posted by Shaggy Hiker

You don't really want the Paint routine to be waiting on a background thread, but that means that your paint event may complete before your calculations.

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I was thinking that the Paint routine would use the actually "known" values, i.e. possibly old data, but why doesn't it show up at all (except for a complete .Invalidate of the Control?).

This one is really bugging me!
I made a small example of what I'm trying to do, and guess what, it is working!
Now I have to look real deep into my application where the failure is. Will report on results.

The small example (Form1 has two Buttons (btnStartStop and btnAdd) and a PictureBox1 and a BGW

Code:

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Public Class Form1

    Private Sub PictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
        Try
            DrawObjects(e.Graphics, MyObjects, Color.Black)
            DrawObjects(e.Graphics, MyObjects2, Color.Red)
        Catch
            Debug.Print("error")
        End Try
    End Sub

    Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        Dim p As New Point(0, 0)
        Dim o As New clEntity("LaLa", p)
        MyObjects.Add(o)
        p = New Point(PictureBox1.Width, 0)
        o = New clEntity("Bla", p)
        MyObjects2.Add(o)
    End Sub

    Private Sub btnStartStop_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnStartStop.Click
        Dim btn As Button = DirectCast(sender, Button)
        If btn.Text = "Start" Then
            btn.Text = "Stop"
            started = True
            GameLoop()
        Else
            btn.Text = "Start"
            started = False
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        MyObjects = New List(Of clEntity)
        MyObjects2 = New List(Of clEntity)
        AddHandler PicBoxInvalidate, AddressOf PictureBox_Invalidate
    End Sub

    Private Sub PictureBox1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PictureBox1.Click
        Dim pic As PictureBox = DirectCast(sender, PictureBox)
        pic.Invalidate()
    End Sub

    Private Sub PictureBox_Invalidate(ByVal sender As Object, ByVal k As KarteEventArgs)
        PictureBox1.Invalidate(k.Region)
    End Sub

    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        MoveObjects(MyObjects, InvalRegions, 1, 1)
    End Sub
   
    Private Sub DrawObjects(g As Graphics, Objects As List(Of clEntity), Color As Color)
        If Not Objects Is Nothing Then
            For Each o As clEntity In Objects
                Using Pen As New Pen(Color)
                    g.DrawLine(Pen, o.Position.X - 3, o.Position.Y, o.Position.X + 3, o.Position.Y)
                    g.DrawLine(Pen, o.Position.X, o.Position.Y - 3, o.Position.X, o.Position.Y + 3)
                End Using
            Next
        End If
    End Sub
End Class

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The module with all the logic. Note that MyObjects.Bewegung (Movement) is calculated using the BGW. MyObjects2.Bewegung is done on the GUI-thread. All the drawing is done in the Paint-Event

Code:

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Module Module1
    Public MyObjects As List(Of clEntity)
    Public MyObjects2 As List(Of clEntity)
    Public Started As Boolean = False
    Public Event PicBoxInvalidate As EventHandler(Of KarteEventArgs)

    Public Class KarteEventArgs
        Inherits EventArgs
        Private _Region As Rectangle
        Public Property Region() As Rectangle
            Get
                Return Me._Region
            End Get
            Set(ByVal value As Rectangle)
                _Region = value
            End Set
        End Property
        Public Sub New(Optional ByVal Region As Rectangle = Nothing)
            Me._Region = Region
        End Sub
    End Class

    Public Sub GameLoop()
        Static LastTime As Integer = Environment.TickCount
        Dim ActualTime As Integer
        Dim FrameIntervall As Integer = 10
        ActualTime = Environment.TickCount
        If LastTime + FrameIntervall <= ActualTime Then
           
            If Not Form1.BackgroundWorker1.IsBusy Then
                Form1.BackgroundWorker1.RunWorkerAsync()
            End If
        End If
        MoveObjects(MyObjects2, InvalRegions, 1, -1)
        LastTime = ActualTime
        If Started = True Then
            ExecuteAfterPause(FrameIntervall, New MethodInvoker(AddressOf GameLoop))
        End If

    End Sub

    Public Sub MoveObjects(ByVal Objects As List(Of clEntity), ByVal Regions As Queue(Of Region), ByVal Vertical As Integer, ByVal Horizontal As Integer)
        If Not Objects Is Nothing Then
            Dim RemoveObjects As New List(Of clEntity)
            For Each o As clEntity In Objects
                Dim size As New Size(8, 8)
                Dim p As New Point(o.Position.X - 4, o.Position.Y - 4)
                Dim k As New KarteEventArgs
                k.Region = New Rectangle(p, size)
                RaiseEvent PicBoxInvalidate(Form1, k) 'to wipe off on the old position
               
                o.Bewegung(Vertical, Horizontal)
               
                p.X = o.Position.X - 3
                p.Y = o.Position.Y - 3
                k.Region = New Rectangle(p, size)
                RaiseEvent PicBoxInvalidate(Form1, k) 'to draw the new position
                'If outside of PictureBox, Remove it
                If o.Position.X > Form1.PictureBox1.Width Or o.Position.X < 0 Or o.Position.Y > Form1.PictureBox1.Height Or o.Position.Y < 0 Then
                    RemoveObjects.Add(o)
                End If
            Next
            If Not RemoveObjects.Count = 0 Then
                For Each o As clEntity In RemoveObjects
                    Objects.Remove(o)
                Next
            End If
        End If
    End Sub
 
End Module

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The clEntity

Code:

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Imports System.Math
Public Class clEntity
   
   

#Region "New Prozeduren"

    Public Sub New(ByVal _Name As String, ByVal _Position As Point)
        With Me
            .Name = _Name
            .Position = _Position
        End With
    End Sub

#End Region

#Region "Eigenschaften"
    Public Mutex As New System.Threading.Mutex
    Private _Name As String
    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(ByVal value As String)
            _Name = value
        End Set
    End Property
    Private _Position As Point
    Public Property Position() As Point
        Get
            Return _Position
        End Get
        Set(ByVal value As Point)
            _Position = value
        End Set
    End Property
 
#End Region

#Region "Methoden"

    Public Sub Bewegung(ByVal Vertical As Integer, ByVal Horizontal As Integer)
        Dim p As New Point(Position.X + Horizontal, Position.Y + Vertical)
        Position = p
    End Sub

#End Region

End Class

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Me.Stupid!
I was precomputing the actual PixelLocation of each object when calculating the movements. That is because I'm using a chart projection that needs much calculation (Mercator). I try to compute each PixelPosition only once, and out of some reasons that does go along with the movement calculus.
By moving that into another thread I missed that I need the correct (centre) position and size of the control. Guess what, I had those values in Public properties of the Form. No problem if you're on a single thread, however........................
All those objects were drawn, however somewhere on a screen in Timbuktu or whatever.

Thanks everybody for the helpfull hints.