As a probably final installment in the thread about optimizing the wx
back-end, here is a post from the wxPython list, in which someone posted
SWIG code for making a PyBuffer from his data set, then using it to
create a wx.Image without copying. A similar approach could be used for
the wxAgg back-end.
-Chris
-------- Original Message --------
Subject: [wxPython-users] Re: using wxImage in C++ python extension
Date: Fri, 18 Aug 2006 16:48:08 +0000 (UTC)
From: Andrew Murray <[EMAIL PROTECTED]>
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<[EMAIL PROTECTED]> <[EMAIL PROTECTED]>
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<[EMAIL PROTECTED]>
Hi all :)
I've followed the combined advice of Robin and Christopher in using a python
buffer object to instance a wx.Image in the python wrapper layer. It
all seems
to be working - and I don't think there are any 'data copies' going on ;)
To keep my underlying C++ python-free, I introduced the buffer (and
creation of
the wx.Image) via my .i Swig file. In case anyone who is reading is
keen trying
to solve a similar problem, I've included the code that I added to my .i
file in
order to implement the change below. (I'd appreciate any comments regarding
errors or shortcomings that anyone spots in my implementation.)
Sorry I didn't reply to the thread earlier. A combination of being tied
up with
more boring work, moving house and background research into using python
buffers
with Swig means that I've only just got this far.
One remaining question I have is: Does the call to wx.EmptyImage that I make
cause any memory to be allocated? I see from Robin's recent post that in my
case this call is now redundant (as I will soon be using
ImageFromBuffer) - but
I'm curious to know the answer anyway ;)
Thanks for all the help. The more I use wxPython the more I like it...
Andrew ;)
/* the RawImage C++ class that we are wrapping offers a method that
returns a pointer to an internal 'unsigned char' buffer of display
data. To make the python class generated by SWIG a bit more
friendly to the rest of our wxPython code we instruct SWIG to make
two modifications during the wrapping process. First we add a
method to the C++ class that will return a version of the internal
display buffer wrapped up as a 'python buffer object' (performing
this in the C++ wrapper class keeps the wrapped C++ python-free)...
*/
%extend RawImage {
PyObject* RawImage::getDisplayBuffer(void) {
// return a new 'python buffer object' that intialised using
// the memory address and length of our display buffer...
void* pvBufferData = (void*)self->pcGetDisplayData();
int iBufferSize = self->getDisplayBufferSize();
return PyBuffer_FromMemory(pvBufferData, iBufferSize);
}
}
/* ... we also add a method to the python wrapper class that will use
the buffer offered by our new C++ method to create a wx.Image
(neither of these methods actually copies the image data)...
*/
%extend RawImage {
%pythoncode %{
def getImage(self):
# create an unintialised wx.Image of the correct size...
wximage = wx.EmptyImage(self.getWidth(), self.getHeight(), clear=False)
# then define the data content of the image...
wximage.SetDataBuffer(self.getDisplayBuffer())
return wximage
%}
}
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