Mask of two overlapped windows

wxPython Users
1

Python 3.11.5
wxPython 4.2.1
Pillow 10.1.0

I would like to make fancy windows (or panels) with Pillow. As you see below, I am having a trouble with mask (or transparency, alpha, …). I also tried “ConvertAlphaToMask” but it didn’t work. I found that the white corners of the inner rectangle is colored by its “BackgroundColour”. What should I do?

import wx
from PIL import Image, ImageDraw

def get_rounded_rectangle_image(width:int, height:int, fill:tuple, outline:tuple):
    factor = 4 # for antialias
    image  = Image.new('RGBA', (factor*width, factor*height), (0, 0, 0, 0))
    draw   = ImageDraw.Draw(image)
    draw.rounded_rectangle(
        (0, 0, factor*width, factor*height),
        fill    = fill,
        outline = outline,
        width   = 20,
        radius  = 200
    )
    image = image.resize((width, height), Image.Resampling.LANCZOS)
    return image

class RoundedWindow(wx.Window):

    def __init__(self, parent:wx.Window, fill:tuple, outline:tuple):
        wx.Window.__init__(self, parent)
        self.fill    = fill
        self.outline = outline
        self.Bind(wx.EVT_SIZE, self.OnSize)
        self.Bind(wx.EVT_PAINT, self.OnPaint)

    def OnSize(self, event):
        event.Skip()
        self.Refresh()

    def OnPaint(self, event):
        dc = wx.PaintDC(self)
        size = dc.GetSize()
        pil_image = get_rounded_rectangle_image(size[0], size[1], self.fill, self.outline)
        wx_image  = wx.Image(size[0], size[1])
        wx_image.SetData(pil_image.convert('RGB').tobytes())
        wx_image.SetAlpha(pil_image.tobytes()[3::4])
        pil_image.close()
        bmp = wx_image.ConvertToBitmap()
        dc.DrawBitmap(bmp, 0, 0, True)

class MainFrame(wx.Frame):

    def __init__(self):
        wx.Frame.__init__(self, None)
        panel   = wx.Panel(self)
        window1 = RoundedWindow(panel  , (255, 0, 0, 255), (0, 0, 0, 255))
        window2 = RoundedWindow(window1, (0, 255, 0, 255), (0, 0, 0, 255))
        sz1 = wx.BoxSizer(wx.HORIZONTAL)
        sz1.Add(window2, 1, wx.EXPAND|wx.ALL, 30)
        window1.SetSizer(sz1)
        sz = wx.BoxSizer(wx.HORIZONTAL)
        sz.Add(window1, 1, wx.EXPAND|wx.ALL, 30)
        panel.SetSizer(sz)
        self.CenterOnScreen()

if __name__ == '__main__':
    app = wx.App()
    MainFrame().Show()
    app.MainLoop()
2

There are a few custom controls in the wx.lib folder (and sub-folders) that use non-rectangular areas for their representation. An example is wx.lib.agw.shapedbutton, but there’s many more.

What happens if you add this line to your event table:

self.Bind(wx.EVT_ERASE_BACKGROUND, lambda x: None)

?

3

SBitmapButton gives the same result.

If I add EVT_ERASE_BACKGROUND, it also shows the same one and goes wrong when I resize the frame.

4

Do you see the same behaviour in the wxPython demo for ShapedButton? If not, I’d suggest looking at the implementation of it.

5

Yes I Do. I made a PNG image file of a rounded rectangle and pass it to shapedbutton.SBitmapButton and saw the exactly same behavior. :frowning:

6

Sorry, that’s not what I meant: if you run the unmodified ShapedButton demo in the wxPython demo, do you see the buttons having the rounded shapes correctly? With the parent background showing through?

7

In some of my code base, I have the following:

                if wx.Platform == '__WXMSW__': # Windows refuses to draw non-transparent rectangle outside of image
                                               # so recreate dc with normal background colour
                    fbmp = wx.Bitmap.FromRGBA(self.bmpw, self.bmph, r, g, b, 0)
                    dc.SetBackground(wx.Brush(self._backgroundcolour))
                    dc.Clear()

I don’t recall how I came to that conclusion/solution but it may help.
My primary reason for suggesting it, is that your code, with PIL minor version changes, works happily on Linux, leading me to assume, it’s a Windows issue.

Regards,
Rolf

p.s. Your code on Linux:
Screenshot at 2024-02-15 20-17-20

1 Like
8

Yes I see the button correctly ONLY IF the parent does not have background image.

9

Oh, I might need to deal with it like you did. Thanks for the advice.