Re: [Pyobjc-dev] Is it possible to create a CFData without copying bytes?

[Uliano G. <gue...@gm...>]

Il giorno 10/nov/07, alle ore 16:24, Ronald Oussoren ha scritto:

>
> On 10 Nov, 2007, at 9:58, Uliano Guerrini wrote:
>
>> Hi,
>> this code:
>>
>> cf=Foundation.CFDataCreate(None,string,len)
>>
>> works as expected, while:
>>
>> cf=Foundation.CFDataCreateWithBytesNoCopy(None,string,len,None)
>>
>> generates crap data. How can I fix this?
>
> both seem to work as expected.

well now that I tried some simple typing on the terminal I have to agree


> What might bite you is that you must make sure that 'string' is kept  
> alive as long as you might access 'cf', Python's garbage collector  
> doesn't (and cannot) know that CFDataCreateWithBytesNoCopy sneeks a  
> reference to part of a Python object in the object it creates.
>
> Could you please create a demo program that demonstrates the problem  
> you're having?

the program for the moment is nonsensic experimenation, here are the  
snippets causing the problem

def newf():
     a=numpy.zeros((256,256),dtype='float32')
     for x in  range(0,256):
         a[:,x]=x/255.0
     return a.tostring()

def cff():
     return Foundation.CFDataCreateWithBytesNoCopy(None,newf(), 
65536*4,None)

def dpf():
     return CGDataProviderCreateWithCFData(cff())

def imf():
     colorspace=CGColorSpaceCreateDeviceGray()
     c=kCGImageAlphaNone | kCGBitmapFloatComponents |  
kCGBitmapByteOrder32Little
     return CGImageCreate(256,256,32,32,256*4,colorspace,c,dpf(),None, 
0,kCGRenderingIntentDefault)

def cii():
     a=CIImage.imageWithCGImage_(imf())
     return a

this core image is then plotted on a view with this method

     def drawRect_(self, rect):
         ciicontext=NSGraphicsContext.currentContext().CIContext()
          
ciicontext.drawImage_inRect_fromRect_(NumpyCFImage.cii(),self.bounds(), 
((0,0),(256,256)))

changing between CFDataCreate and CFDataCreateWithBytesNoCopy makes  
the difference from expected image and crapy noise

uliano

>