Q about images, Refresh() and Layout()

Michael Eager <[email protected]> Mon, 10 Aug 2020 12:52:16 -0700

Newsgroups	gmane.comp.python.wxpython
Message-ID	<[email protected]>

I'm pretty confused about the differences between the
wx.Frame::Refresh() and Layout() functions. And maybe Update(), as well.

I have an small test application where I create a panel and add an
wx.StaticBitmap to it, using a BoxSizer to center the image on the
panel. Initially, the image is blank. When I start the app, the blank
image is displayed centered on the screen as expected.

When I update the image control with a wx.Bitmap, and then call
Refresh(), the updated image is displayed in the top left corner. The
new image fits within the original blank image, although it may not be
exactly the same size. If I call Layout(), the updated image is
displayed correctly.

My expectation was that calling Refresh() would redraw the image (and
everything else on the panel) without changing where the widget was
located. That doesn't appear to be the case. Calling Layout() should
recalculate the position of widgets, without redrawing the panel. That
also isn't happening in the way I expected.

Can someone give me a clue what is really happening?

I've attached my test program.

Is there a way to update the image in a StaticBitmap without redrawing
everything in the panel or recomputing the layout? For example, if I
have a panel with a number of thumbnail images, it seems that I would
want to update each one without having to redo the layout.

--
Michael Eager

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try.py (text/x-python, 2.1 KB)

import wx

class MainFrame(wx.Frame):
    def __init__(self):
        super().__init__(None, -1, title="File Browser", size=(1000,1000))

        #self.image_panel = ImagePanel(self, size=(200, 200))
        self.image_panel = ImagePanel(self)

        browseBtn = wx.Button(self, label='Browse')
        browseBtn.Bind(wx.EVT_BUTTON, self.onBrowse)

        vbox = wx.BoxSizer(wx.VERTICAL, )
        vbox.Add(self.image_panel, 1, wx.ALL|wx.EXPAND, 5)
        vbox.Add(browseBtn, 0, wx.ALL, 5)

        self.SetSizer(vbox)
        self.Layout()
        self.Show()

    def onBrowse(self, event):
        """
        Browse for file
        """
        wildcard = "JPEG files (*.jpg)|*.jpg"
        dialog = wx.FileDialog(None, "Choose a file",
                               wildcard=wildcard,
                               style=wx.FD_OPEN)
        if dialog.ShowModal() == wx.ID_OK:
            self.image_panel.loadImage(dialog.GetPath())
        dialog.Destroy()

class ImagePanel(wx.Panel):
    def __init__(self, parent):
        super().__init__(parent, style=wx.BORDER_DOUBLE)

        self.maxsize = 200

        img = wx.Image((400,400))
        empty = wx.EmptyBitmap(200,200)
        dc = wx.MemoryDC(empty)
        dc.SetBackground(wx.Brush("white"))
        dc.Clear()
        self.image_ctrl = wx.StaticBitmap(self, bitmap=empty)

        main_sizer = wx.BoxSizer(wx.VERTICAL)
        main_sizer.Add(self.image_ctrl, 1, wx.ALL|wx.ALIGN_CENTER_HORIZONTAL|wx.SHAPED, 5)

        self.SetSizerAndFit(main_sizer)

    def loadImage(self, filepath):
        img = wx.Image(filepath, wx.BITMAP_TYPE_ANY)

        w = img.GetWidth()
        h = img.GetHeight()
        print ("w = %d, h = %d" % (w, h))

        if w > h:
            W = self.maxsize
            H = self.maxsize * h / w
        else:
            H = self.maxsize
            W = self.maxsize * w / h
        img = img.Scale(int(W), int(H))

        self.image_ctrl.SetBitmap(wx.Bitmap(img))
        #self.Refresh()
        self.Layout()

def main():
    app = wx.App()
    fr = MainFrame()
    fr.Show()
    app.MainLoop()

if __name__ == '__main__':
    main()