Drawable scrollable window not rendering

Question

I'm working on a project in which I want to draw stuff on a bitmap inside a ScrolledWindow.

It works fine, I can draw lines, but when I scroll the window and try to draw something, it is not rendering. The newly drawed line will only be rendered when I "move away" (like scroll back to 0, 0) and then come back.

I've come accross a few (pretty old) questions on SO but it seems that no one have had that problem.

Here's an example a code example:

import wx


class MainFrame(wx.Frame):

    def __init__(self, *args, **kw):
        wx.Frame.__init__(self, *args, **kw)
        s = wx.BoxSizer(wx.VERTICAL)
        panel = DrawablePanel(self)
        s.Add(panel, 1, wx.EXPAND)
        self.SetSizer(s)
        self.SetSize(400, 400)


class DrawablePanel(wx.ScrolledWindow):

    def __init__(self, parent):
        super().__init__(parent, id=wx.ID_ANY)
        self.SetScrollbars(10, 10, 100, 100)

        self.buffer = wx.Bitmap((1000, 1000))
        cdc = wx.ClientDC(self)
        self.DoPrepareDC(cdc)
        dc = wx.BufferedDC(cdc, self.buffer)
        dc.Clear()

        self.mouse_pos = None

        self.Bind(wx.EVT_PAINT, self.on_paint)
        self.Bind(wx.EVT_LEFT_DOWN, self.on_mouse_down)
        self.Bind(wx.EVT_MOTION, self.on_motion)

    def on_paint(self, evt):
        wx.BufferedPaintDC(self, self.buffer, wx.BUFFER_VIRTUAL_AREA)

    def on_mouse_down(self, evt):
        self.mouse_pos = self.CalcUnscrolledPosition(evt.GetPosition()).Get()

    def on_motion(self, evt):
        if evt.Dragging() and evt.LeftIsDown():
            new_pos = self.CalcUnscrolledPosition(evt.GetPosition()).Get()
            coord = self.mouse_pos + new_pos
            client_device = wx.ClientDC(self)
            self.DoPrepareDC(client_device)
            dc = wx.BufferedDC(client_device, self.buffer)
            dc.DrawLine(*coord)
            self.mouse_pos = new_pos


if __name__ == "__main__":
    app = wx.App()
    wx.InitAllImageHandlers()
    MainFrame(None).Show()
    app.MainLoop()

Any help would really be appreciated. Thanks in advance,

Jeremy

Answer 1

Simply add a 'Refresh' command for the panel window:

Refresh(self, eraseBackground=True, rect=None) Causes this window, and all of its children recursively, to be repainted.

def on_motion(self, evt):
    if evt.Dragging() and evt.LeftIsDown():
        new_pos = self.CalcUnscrolledPosition(evt.GetPosition()).Get()
        coord = self.mouse_pos + new_pos
        client_device = wx.ClientDC(self)
        self.DoPrepareDC(client_device)
        dc = wx.BufferedDC(client_device, self.buffer)
        dc.DrawLine(*coord)
        self.mouse_pos = new_pos
    self.Refresh()