title: wxPython - Resizing an image with the EVT_SIZE event of its parent panel
body: <p>My previous attempt at asking this question was horrible and I had also made some progress, please bear with me, I did not intend to re-ask this so many times, and it is not my style.</p>
  
  <p>Here is the final version:  I am resizing a window that contains a DC Client painted bitmap and on the EVT_SIZE event, I am resizing it by re-scaling it (using scale, not rescale) and re-painting the image.  The problem is it does not appear as though its respecting the aspect ratio even though I am calculating w/h for it.  Also when it grows in height the image is distorted.  Finally, when another window passes over it, the image goes white.  Any ideas how to fix any of these issues?  My window/image class is below:</p>
  
  <pre><code>class TransactionImage(wx.Window):
      def __init__(self, parent, fname, name):
          wx.Window.__init__(self, parent, name=name)
  
          self.dc = wx.ClientDC(self)  
  
          self.load_image(fname)
          cursor = wx.StockCursor(wx.CURSOR_MAGNIFIER)
          self.SetCursor(cursor)
  
          self.Bind(wx.EVT_SIZE, self.resize_space)
  
  
      def load_image(self, image):
          self.image = wx.Image(image, wx.BITMAP_TYPE_JPEG)
          (w, h) = self.image.GetSize()
          self.image_ar = w/h
  
      def resize_space(self, size):
          (w, h) = self.get_best_size()
          self.s_image = self.image.Scale(w, h)
          self.bitmap = wx.BitmapFromImage(self.s_image)
          self.dc.DrawBitmap(self.bitmap, 0, 0, useMask=False)
          # how can I 'refresh this area to make it 'fit'
  
      def get_best_size(self):
          (window_width, window_height) = self.GetSizeTuple()
          new_height = window_width / self.image_ar
          new_size = (window_width, new_height)
          return new_size
  </code></pre>
  
  <p>Also, I am having trouble understanding how to properly use the Client DC.  I want to refresh the window area before re-drawing the next image, because if i dont i get weird risiduals and it looks bad.  In order to fix this I tried using dc.Clear which cleans the background off.  However, doing so on every size call as i would need to causes the image to flash white a million times while im re-sizing.  how can i avoid this?</p>
  
  <p>EDIT - </p>
  
  <p>In response to Umyal's comment response - here is a very simplified version of my application.  Either way I class my window generator for the images the size handler re-scaling the images causes the image to flicker badly, creating an unappealing artifact.  Also, when another frame passes over the application, the image display becomes white, as if been erased.</p>
  
  <p>I was thinking as a way around this - I could implement the solution windows image viewer seems to have, which is the image is only rescaled and repainted when the user lets go of the edge of the frame when resizing it.  Problem with that solution is that there is no clear way to detect when the user stops resizing the frame. (wxEVT_SIZE, wxEVT_SIZING)</p>
  
  <p>Here is the simplified application code, you will need to find your own images and the bigger the better.  The original image dimentions are 3872 x 2592</p>
  
  <pre><code># this is required for 'real' math - derive the 'aspect ratio'
  from __future__ import division
  import wx
  
  class TransactionImage(wx.Window):
      def __init__(self, parent, fname, name):
          wx.Window.__init__(self, parent, name=name)
  
          self.load_image(fname)
          cursor = wx.StockCursor(wx.CURSOR_MAGNIFIER)
          self.SetCursor(cursor)
  
          self.Bind(wx.EVT_SIZE, self.resize_space)
          self.Bind(wx.EVT_PAINT, self.on_paint)
  
      def load_image(self, image):
          self.image = wx.Image(image, wx.BITMAP_TYPE_JPEG)
          (w, h) = self.image.GetSize()
          self.image_ar = w/h
          self.bitmap = wx.BitmapFromImage(self.image)
  
      def resize_space(self, event):
          (w, h) = self.get_best_size()
          self.s_image = self.image.Scale(w, h)
          self.bitmap = wx.BitmapFromImage(self.s_image)
  
      def on_paint(self, event):
          self.dc = wx.PaintDC(self)
          self.dc.DrawBitmap(self.bitmap, 0, 0, useMask=False)
  
      def get_best_size(self):
          (window_width, window_height) = self.GetSizeTuple()
          new_height = window_width / self.image_ar
          new_size = (window_width, new_height)
          return new_size
  
  
  class OriginalTransactionImage(wx.Window):
      def __init__(self, parent, fname, name):
          wx.Window.__init__(self, parent, name=name)
  
          self.dc = wx.ClientDC(self)  
  
          self.load_image(fname)
          cursor = wx.StockCursor(wx.CURSOR_MAGNIFIER)
          self.SetCursor(cursor)
  
          self.Bind(wx.EVT_SIZE, self.resize_space)
  
  
      def load_image(self, image):
          self.image = wx.Image(image, wx.BITMAP_TYPE_JPEG)
          (w, h) = self.image.GetSize()
          self.image_ar = w/h
  
      def resize_space(self, size):
          (w, h) = self.get_best_size()
          self.s_image = self.image.Scale(w, h)
          self.bitmap = wx.BitmapFromImage(self.s_image)
          self.dc.DrawBitmap(self.bitmap, 0, 0, useMask=False)
  
      def get_best_size(self):
          (window_width, window_height) = self.GetSizeTuple()
          new_height = window_width / self.image_ar
          new_size = (window_width, new_height)
          return new_size
  
  
  class ImageBrowser(wx.Frame):
  
      def __init__(self, image1, image2, parent=None, id=wx.ID_ANY,
                   pos=wx.DefaultPosition, title='Image Browser'):
          size = (1500, 800)
          wx.Frame.__init__(self, parent, id, title, pos, size)
  
          self.CentreOnScreen()
  
          self.panel = wx.Panel(self, wx.ID_ANY)
          self.panel.SetBackgroundColour(wx.Colour(191,197,229))
  
          self.main_sizer = wx.BoxSizer(wx.VERTICAL)
  
          self.image_panel = wx.Panel(self.panel, wx.ID_ANY, style=wx.SIMPLE_BORDER)
          self.image_panel.SetBackgroundColour(wx.Colour(255, 255, 255))
  
          self.image_sizer = wx.BoxSizer(wx.HORIZONTAL)
          self.image_panel.SetSizer(self.image_sizer)
  
          self.load_image_sizer(image1, image2)
          self.main_sizer.Add(self.image_panel, 1, wx.GROW|wx.ALIGN_CENTER|wx.ALL, 25)
          self.panel.SetSizer(self.main_sizer)
  
  
      def load_image_sizer(self, image1, image2):
          #bitmap1 = OriginalTransactionImage(self.image_panel, image1, 'image1')
          #bitmap2 = OriginalTransactionImage(self.image_panel, image2, 'image2')
  
          bitmap1 = TransactionImage(self.image_panel, image1, 'image1')
          bitmap2 = TransactionImage(self.image_panel, image2, 'image2')
  
          self.image_sizer.Add(bitmap1, 1, wx.GROW|wx.ALIGN_LEFT|wx.ALL, 20)
          self.image_sizer.Add(bitmap2, 1, wx.GROW|wx.ALIGN_RIGHT|wx.ALL, 20)
  
  
  class IBApp(wx.App):
  
      def OnInit(self):
          img1 = "0_3126_image1.jpeg"
          img2 = "0_3126_image2.jpeg"
  
          ib = ImageBrowser(img1, img2)
          ib.Show()
          self.SetTopWindow(ib)        
          return True
  
  app = IBApp(False, None)
  app.MainLoop()
  </code></pre>