Python - Per pixel alpha - UpdateLayeredWindow

[Alexandru Ionescu]

Hello,

In the last two weeks I've been trying to properly use UpdateLayeredWindow in Python but I'm only getting errors. I want to make a quality window with per pixel alpha graphics. I tried with ctypes and I also tried with win32gui & win32api. I got all kinds of errors. In the end I got the error code 5 (ERROR_ACCESS_DENIED) and nothing appears on the screen.
Here is my latest code (made with ctypes):

import wx
import win32api    #for RGB
import ctypes
 
cUser32 = ctypes.windll.user32
cGdi32 = ctypes.windll.gdi32
cKernel32 = ctypes.windll.kernel32
 
class POINT(ctypes.Structure):
    _fields_ = [("x", ctypes.c_int), ("y", ctypes.c_int)]
 
class SIZE(ctypes.Structure):
    _fields_ = [("cx", ctypes.c_int), ("cy", ctypes.c_int)]
 
class BLENDFUNCTION(ctypes.Structure):
    _fields_ = [("AlphaFormat", ctypes.c_int), ("BlendFlags", ctypes.c_int),("BlendOp", ctypes.c_int),("SourceConstantAlpha", ctypes.c_int)]
 
ULW = cUser32.UpdateLayeredWindow
ULW.argtypes = [ctypes.c_ulong,
                ctypes.c_ulong,
                ctypes.POINTER(POINT),
                ctypes.POINTER(SIZE),
                ctypes.c_ulong,
                ctypes.POINTER(POINT),
                ctypes.c_ulong,
                ctypes.POINTER(BLENDFUNCTION),
                ctypes.c_ulong]
 
ULW.restype = ctypes.c_long
 
GWL_EXSTYLE = 0xFFFFFFEC
WS_EX_LAYERED = 0x00080000
WS_EX_TRANSPARENT = 0x00000020
LWA_ALPHA = 0x00000002
LWA_COLORKEY = 0x00000001
AC_SRC_ALPHA = 0x01
AC_SRC_OVER = 0x00
 
class MyFrame(wx.Frame):
    def __init__(self):
        wx.Frame.__init__(self, None, wx.ID_ANY, title = "Test")
 
        hwnd = self.GetHandle()        
        print hwnd        
        gwl = cUser32.GetWindowLongA(hwnd, GWL_EXSTYLE)
        print gwl
        print cUser32.SetWindowLongA(hwnd, GWL_EXSTYLE, (gwl | WS_EX_LAYERED))
        print cKernel32.GetLastError()
 
        self.bmp = wx.EmptyBitmap(800,600)
 
        jpg1 = wx.Image('Multiple alpha.png', wx.BITMAP_TYPE_PNG)
        self.bmp = jpg1.ConvertToBitmap()
        w1, h1 = self.bmp.GetWidth(), self.bmp.GetHeight()
        self.SetClientSize( (w1, h1) )
 
        screenDC = cUser32.GetDC(None)
        cScreenDC = cGdi32.CreateCompatibleDC(screenDC)
        cGdi32.SelectObject(cScreenDC, self.bmp.GetHandle())
        p = POINT(50,50)
        p2 = POINT(0,0)
        s = SIZE(816,612)
        blend = BLENDFUNCTION(AC_SRC_OVER,0,AC_SRC_ALPHA,200)
 
        crkey = win32api.RGB(255,255,255)
        flags = (LWA_ALPHA | LWA_COLORKEY)
 
        print cUser32.UpdateLayeredWindow(hwnd,
                                          screenDC,
                                          ctypes.byref(p),
                                          ctypes.byref(s),
                                          cScreenDC,
                                          ctypes.byref(p2),
                                          crkey,
                                          ctypes.byref(blend),
                                          flags)
 
        print cKernel32.GetLastError()
 
app = wx.App()
frame = MyFrame()
frame.Show()
app.SetTopWindow(frame)
app.MainLoop()
 
 

You can find a multi layer PNG at the following link
http://en.wikipedia.org/wiki/File:PNG_transparency_demonstration_1.png

I also attached this image and the code (in a .pyw file).

My email address is [e-mail]

Thank you,
Alex