在單獨的線程中在圖像緩衝區（MemoryDC）上繪圖

Question

我有：使用Cairo繪製窗體時使用圖像緩衝區的面板。 緩衝實現，就像這裏的例子：http://wiki.wxpython.org/BufferedCanvas

我想：一個線程它做所有的繪圖緩衝區時，更新（創建/調整/縮放）

的問題：什麼是解決這個問題的好方法嗎？

我已經嘗試在線程中繪製本身，並且因爲直流沒有完成而出現斷言錯誤。 我是否必須在線程或其中創建DC？ 有關於線程和DC的一些教程嗎？

編輯：

我試圖合併與BufferedCanvas的例子，這樣的：LongRunningTasks

在這裏看到：http://pastebin.com/X9kqSMKT

有時它給X Window系統錯誤，有時工作不正常

感謝您的幫助

Answer 1

這裏是一個3面板的例子。首先使用Paint和Resize事件繪製。其次使用雙緩衝，所以它不閃爍。第三個使用另一個線程繪製位圖，並在Paint事件中顯示位圖。

import wx 
from wx.lib.delayedresult import startWorker 
import array 

#============================================================================= 
class DrawPanel(wx.Panel): 
    """ 
    Basic panel with graphics drawn in Pain Event 
    """ 
    def __init__(self, *args, **kwargs): 
     wx.Panel.__init__(self, *args, **kwargs) 

     self.Bind(wx.EVT_PAINT, self.OnPaint) 
     self.Bind(wx.EVT_SIZE, self.OnSize) 
     self.Bind(wx.EVT_ERASE_BACKGROUND, self.OnEraseBackground) 

    #------------------------------------------------------------------------- 
    def OnPaint(self, event): 
     dc = wx.PaintDC(self) 
     dc.SetBackground(wx.Brush(wx.BLACK)) 
     dc.Clear() 
     w, h = self.GetClientSizeTuple() 
     dc.DrawCirclePoint((w/2, h/2), 50) 

    #------------------------------------------------------------------------- 
    def OnSize(self, event): 
     self.Refresh() 
     self.Update() 

    #------------------------------------------------------------------------- 
    def OnEraseBackground(self, event): 
     pass # Or None 

#============================================================================= 
class DrawPanelDB(wx.Panel): 
    """ 
    Basic panel with graphics drawn in Pain Event using Double Buffering 
    """ 
    def __init__(self, *args, **kwargs): 
     wx.Panel.__init__(self, *args, **kwargs) 

     self.Bind(wx.EVT_PAINT, self.OnPaint) 
     self.Bind(wx.EVT_SIZE, self.OnSize) 
     self.Bind(wx.EVT_ERASE_BACKGROUND, self.OnEraseBackground) 

    #------------------------------------------------------------------------- 
    def OnPaint(self, event): 
     # Switches the buffers when 'dc' goes out of scope 
     dc = wx.BufferedPaintDC(self) 
     dc.SetBackground(wx.Brush(wx.BLACK)) 
     dc.Clear() 
     w, h = self.GetClientSizeTuple() 
     dc.DrawCirclePoint((w/2, h/2), 50) 

    #------------------------------------------------------------------------- 
    def OnSize(self, event): 
     self.Refresh() 
     self.Update() 

    #------------------------------------------------------------------------- 
    def OnEraseBackground(self, event): 
     pass # Or None 

#============================================================================= 
class DrawPanelDBT(wx.Panel): 
    """ 
    Complex panel with its content drawn in another thread 
    """ 
    def __init__(self, *args, **kwargs): 
     wx.Panel.__init__(self, *args, **kwargs) 

     self.t = None 
     self.w, self.h = self.GetClientSizeTuple() 
     self.buffer = wx.EmptyBitmap(self.w, self.h) 

     self.Bind(wx.EVT_PAINT, self.OnPaint) 
     self.Bind(wx.EVT_SIZE, self.OnSize) 
     self.Bind(wx.EVT_ERASE_BACKGROUND, self.OnEraseBackground) 

     self.timer = wx.Timer(self) 
     self.Bind(wx.EVT_TIMER, self.OnTimer, self.timer) 

     self.SizeUpdate() 

    #------------------------------------------------------------------------- 
    def OnPaint(self, event): 
     # Just draw prepared bitmap 
     wx.BufferedPaintDC(self, self.buffer) 

    #------------------------------------------------------------------------- 
    def OnSize(self, event): 
     self.w, self.h = self.GetClientSizeTuple() 
     self.buffer = wx.EmptyBitmap(self.w, self.h) 
     self.Refresh() 
     self.Update() 
     # After drawing empty bitmap start update 
     self.SizeUpdate() 

    #------------------------------------------------------------------------- 
    def OnEraseBackground(self, event): 
     pass # Or None 

    #------------------------------------------------------------------------- 
    def OnTimer(self, event): 
     # Start another thread which will update the bitmap 
     # But only if another is not still running! 
     if self.t is None: 
      self.timer.Stop() 
      self.t = startWorker(self.ComputationDone, self.Compute) 

    #------------------------------------------------------------------------- 
    def SizeUpdate(self): 
     # The timer is used to wait for last thread to finish 
     self.timer.Stop() 
     self.timer.Start(100) 

    #------------------------------------------------------------------------- 
    def Compute(self): 
     # Compute Fractal 
     MI = 20 

     def mapme(x, minimal, maximal, newmin, newmax): 
      return(((float(x) - minimal)/(maximal - minimal)) 
        * (newmax - newmin) + newmin) 

     def compute(x, y): 
      z = complex(0, 0) 
      c = complex(x, y) 
      for i in range(MI): 
       z = z**2 + c 
       if abs(z) > 2: 
        return i+1 
      return 0 

     def color(i): 
      a = int(mapme(i, 1, MI, 0, 255)) 
      return(a, a, a) 

     def compute_buff(x1, x2, y1, y2, w, h): 
      buffer = array.array('B') 
      for y in range(h): 
       for x in range(w): 
        i = compute(mapme(x, 0, w, x1, x2), 
           mapme(y, 0, h, y2, y1)) 
        if i == 0: 
         buffer.extend((255, 255, 255)) 
        else: 
         buffer.extend(color(i)) 
      return buffer 

     width, height = self.w, self.h 
     x = -0.5 
     y = 0.0 
     w = 2.4 
     h = w * height/width 
     data = compute_buff(x - w/2, x + w/2, y - h/2, y + h/2, width, height) 
     temp_buffer = wx.BitmapFromBuffer(width, height, data) 
     return temp_buffer 

    #------------------------------------------------------------------------- 
    def ComputationDone(self, r): 
     # When done, take bitmap and place it to the drawing buffer 
     # Invalidate panel, so it is redrawn 
     # But not if the later thread is waiting! 
     temp = r.get() 
     if not self.timer.IsRunning(): 
      self.buffer = temp 
      self.Refresh() 
      self.Update() 
     self.t = None 

#============================================================================= 
class MainWindow(wx.Frame): 
    def __init__(self, *args, **kwargs): 
     wx.Frame.__init__(self, *args, **kwargs) 
     self.panel = wx.Panel(self) 
     self.drawing = DrawPanel(self.panel, size=(300, 300)) 
     self.drawingDB = DrawPanelDB(self.panel, size=(300, 300)) 
     self.drawingDBT = DrawPanelDBT(self.panel, size=(300, 300)) 
     self.sizerPanel = wx.BoxSizer() 
     self.sizerPanel.Add(self.panel, proportion=1, flag=wx.EXPAND) 
     self.sizerMain = wx.BoxSizer() 
     self.sizerMain.Add(self.drawing, 1, wx.ALL | wx.EXPAND, 5) 
     self.sizerMain.Add(self.drawingDB, 1, wx.ALL | wx.EXPAND, 5) 
     self.sizerMain.Add(self.drawingDBT, 1, wx.ALL | wx.EXPAND, 5) 
     self.panel.SetSizerAndFit(self.sizerMain) 
     self.SetSizerAndFit(self.sizerPanel)  
     self.Show() 

app = wx.App(False) 
win = MainWindow(None) 
app.MainLoop()