從一個單獨的線程繪畫？

Question

我目前正在使用圖形類創建遊戲中所有圖片的遊戲，我也試圖從單獨的線程中繪製圖片來阻止我的主線程凍結。但每次我嘗試運行程序時，窗體出現什麼也沒有它，我得到這個錯誤...

System.NullReferenceException：對象不設置到對象的實例。

在Single_Player.Form1.mainPaint（PaintEventArgs的E）在C：\用戶\塞繆爾\文件\視覺工作室2012 \項目\ Single_Player \ Single_Player \ Form1.vb的：行12

如果我的代碼做的工作，我期待它在屏幕上移動一個橢圓，反正這是我的代碼...

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load 
    Dim paintT As New Threading.Thread(AddressOf mainPaint) 
    paintT.Start() 
End Sub 

Private Sub mainPaint(e As PaintEventArgs) 
    e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias 
    e.Graphics.CompositingQuality = Drawing2D.CompositingQuality.HighQuality 
    Dim playerX As Integer = 0 
    Dim playerY As Integer = 206 
    Do While 0/0 
     e.Graphics.DrawRectangle(New Pen(Color.FromArgb(128, Color.Black)), 0, 0, 884, 24) 
     e.Graphics.FillRectangle(New SolidBrush(Color.FromArgb(128, Color.Black)), 0, 0, 884, 24) 
     e.Graphics.DrawString("Life: 5", New Font("DigifaceWide", 20, GraphicsUnit.Pixel), New SolidBrush(Color.FromArgb(191, Color.Green)), 2, 0) 
     e.Graphics.DrawString("Score: 0", New Font("DigifaceWide", 20, GraphicsUnit.Pixel), New SolidBrush(Color.FromArgb(191, Color.White)), 100, 0) 
     e.Graphics.FillEllipse(New SolidBrush(Color.FromArgb(128, Color.Blue)), playerX, playerY, 24, 24) 
     playerX = playerX + 1 
     playerY = playerY + 1 
     e.Graphics.Clear(Color.Transparent) 
     Threading.Thread.Sleep(50) 
    Loop 
End Sub 

更新（再次） 我到目前爲止的代碼（這時候我已經通過設計窗口中增加了一個定時器）...

Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles Me.Shown 
    Timer1.Interval = 50 
    Timer1.Start() 
End Sub 

Private Sub mainBackgroundPB_Paint(sender As Object, e As PaintEventArgs) Handles Timer1.Tick 
    e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias 
    e.Graphics.CompositingQuality = Drawing2D.CompositingQuality.HighQuality 
    e.Graphics.DrawRectangle(New Pen(Color.FromArgb(128, Color.Black)), 0, 0, 884, 24) 
    e.Graphics.FillRectangle(New SolidBrush(Color.FromArgb(128, Color.Black)), 0, 0, 884, 24) 
    e.Graphics.DrawString("Life: 5", New Font("DigifaceWide", 20, GraphicsUnit.Pixel), New SolidBrush(Color.FromArgb(191, Color.Green)), 2, 0) 
    e.Graphics.DrawString("Score: 0", New Font("DigifaceWide", 20, GraphicsUnit.Pixel), New SolidBrush(Color.FromArgb(191, Color.White)), 100, 0) 
    e.Graphics.FillEllipse(New SolidBrush(Color.FromArgb(128, Color.Blue)), playerX, playerY, 24, 24) 
    playerX = playerX + 1 
    playerY = playerY + 1 
    e.Graphics.Clear(Color.Transparent) 
End Sub 

Answer 1

你不能在工作線程漆，窗戶根本線程安全的。計時器滴答事件處理程序會在計時器滴答時崩潰並燒燬。 Tick事件沒有PaintEventArgs參數。

只有Paint事件有這些參數，添加事件和移動你的代碼。您可以使用計時器觸發繪畫，使事件處理程序如下所示：

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick 
    Me.Invalidate() 
End Sub 

Answer 2

上面的答案不正確。它CAN來完成，然後將其CAN可以做得更爲出色。

定時器，以預設間隔，它可以很好的對predictabilitys起見運行，但不利於性能，因爲它總是會以相同的速度或更慢運行。定時器在遊戲中是昂貴的，所以要相應地使用它們，如果有的話。

下面是一個簡單的例子我寫了表示在一個線程繪製，其傳遞到一個委託和使用掃描層寫入圖像到主UI。

改進建議被註釋爲好。

Public Class Form1 

Enum enumGameObjectTypes 
    RedBox = 0 
    BlueBox = 1 
    YellowCircle = 2 
End Enum 

Structure structGameObjects 
    Dim Type As enumGameObjectTypes 
    Dim Location As Point 
End Structure 

' When you have global variables, they are accessible outside the thread. 
' You cannot access them on the drawing thread however, without using SyncLock to lock 
' the object. 
Public GameObjects As New List(Of structGameObjects) 
Public tDrawingThread As New System.Threading.Thread(AddressOf DrawingThread) 

' We have to use delegates to pass the image 
Delegate Sub DrawingDelegateSub(TheDrawnImage As Image) 
Public DrawingDelegate As DrawingDelegateSub 

' Set this to true when it's time to exit cleanly 
Public _ExitThreadSafelyNow As Boolean = False 

Public Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load 
    Dim rand As New Random 

    For cnt = 1 To rand.Next(5, 20) 
     ' Create some game objects 
     Dim newObj As New structGameObjects 
     With newObj 
      .Type = rand.Next(0, 2) 
      .Location = New Point(rand.Next(0, cnt * 100), rand.Next(0, cnt * 50)) 
     End With 
    Next 

    ' Set up a delegate (basically a worker that can "move data between threads" safely) 
    DrawingDelegate = AddressOf DrawImage 

    ' Start the thread 
    tDrawingThread.Start() 
End Sub 

Public Sub DrawImage(ByVal DrawnImage As Bitmap) 

    Dim tmpImage As New Bitmap(1024, 768) 

    ' Draw the image to the picture box using an intermediary layer... 
    ' The reason we dont just say pb.Image = DrawnImage is because the bitmaps are passed by pointer references NOT just by the image 
    ' So, passing it direct would be non-thread safe. 
    ' 
    ' This also isn't the *right* way to do this, but it is just an example. 
    ' 
    ' What we're doing is all the heavy lifting in the thread and then we're scanning pixel by pixel through the image drawn by the thread. 
    ' 
    ' The performance here will be awful, so the fix; if you can understand how it works, is to use Bitmap.LockBits; 
    ' Performance will ramp up 1000x right away. https://msdn.microsoft.com/en-us/library/5ey6h79d(v=vs.110).aspx 
    For x = 1 To DrawnImage.Width - 1 
     For y = 1 To DrawnImage.Height - 1 
      tmpImage.SetPixel(x, y, DrawnImage.GetPixel(x, y)) 
     Next 
    Next 

    pb.Image = tmpImage 
    Debug.Print("Wrote frame !") 
End Sub 

' Main drawing loop 
Sub DrawingThread() 
    Dim rectBounds As New Rectangle(0, 0, 1024, 768) 

    ' 
    ' 
    Do Until _ExitThreadSafelyNow = True 

     ' Set up the next frame 
     Dim ImageBuffer As New Bitmap(rectBounds.Width, rectBounds.Height) 
     Dim g As Graphics = Graphics.FromImage(ImageBuffer) ' Create the graphics object 
     g.FillRectangle(Brushes.Black, rectBounds) 

     ' Lock the gameobjects object until we're done using it. 
     SyncLock GameObjects 
      For Each obj In GameObjects 
       Select Case obj.Type 
        Case enumGameObjectTypes.RedBox 
         g.FillRectangle(Brushes.Red, New Rectangle(obj.Location.X, obj.Location.Y, 15, 15)) 
         ' 
        Case enumGameObjectTypes.BlueBox 
         g.FillRectangle(Brushes.Blue, New Rectangle(obj.Location.X, obj.Location.Y, 20, 20)) 
         ' 
        Case enumGameObjectTypes.YellowCircle 
         g.FillEllipse(Brushes.Yellow, New Rectangle(obj.Location.X, obj.Location.Y, 15, 15)) 
         ' 
        Case Else 
         g.FillEllipse(Brushes.Pink, New Rectangle(obj.Location.X, obj.Location.Y, 15, 15)) 
       End Select 
      Next 
     End SyncLock 


     '/// All done drawing by this point... 

     'TODO: Eventually implement Bitmap.LockBits here! 


     SyncLock ImageBuffer 
      ' Send the image onto the main thread. 
      Call DrawingDelegate(ImageBuffer) 
     End SyncLock 


    Loop 
End Sub 

Private Sub Form1_Closing(sender As Object, e As CancelEventArgs) Handles Me.Closing 

    _ExitThreadSafelyNow = True 
End Sub 
End Class