Creating a bitmap with alpha channel

wxPython Users
1

Hi,

I have to draw an alpha blended rectangle on a wxPanel ... I tryed creating an empty bitmap, drawing on it a rectangle and then setting the alpha for the whole pixels. But wxPython gives a an assertion error:

PyAssertionError: C++ assertion "wxAssertFailure" failed in ..\..\src\common\image.cpp(948): invalid image or no alpha channel

I use this code (maybe its wrong ...):

bmp = wx.EmptyBitmap(w, h)
dc = wx.MemoryDC()
dc.SelectObject(bmp)
dc.SetBrush(wx.RED_BRUSH)
dc.SetPen(wx.RED_PEN)
dc.DrawRectangle(0, 0, w, h)

image = bmp.ConvertToImage()
for x in range(0, w):
  for y in range(0, h):
   image.SetAlpha(x, y, 120)

bmp = image.ConvertToBitmap()

and then a draw 'bmp' ... but it stops and 'image.SetAlpha(x, y, 120)'

what's wrong? How can I do?

bye

2

Gabriele Farina *DarkBard* wrote:

PyAssertionError: C++ assertion "wxAssertFailure" failed in ..\..\src\common\image.cpp(948): invalid image or no alpha channel

I use this code (maybe its wrong ...):

bmp = wx.EmptyBitmap(w, h)
dc = wx.MemoryDC()
dc.SelectObject(bmp)
dc.SetBrush(wx.RED_BRUSH)
dc.SetPen(wx.RED_PEN)
dc.DrawRectangle(0, 0, w, h)

image = bmp.ConvertToImage()
for x in range(0, w):
for y in range(0, h):
  image.SetAlpha(x, y, 120)

bmp = image.ConvertToBitmap()

and then a draw 'bmp' ... but it stops and 'image.SetAlpha(x, y, 120)'

what's wrong? How can I do?

Call image.InitAlpha() first.

···

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Robin Dunn
Software Craftsman
http://wxPython.org Java give you jitters? Relax with wxPython!