How do I use the unpack function?

[Marlin Rowley]

Gary,

I'm getting streaming tile data from a renderer in order to allow the user to see the rendering of tiles in real-time to create the total image.  I'm NOT reading an entire image scanline-by-scanline.  The renderer streams in a series of floats (for each tile) and I build this tile up from each individual color component passed in.  I then convert it to a small bitmap and blit() it to the window that will eventually make up my entire image.  I'm just wanting to make the process as fast as the renderer can render the tiles.  I've noticed on scenes that aren't very complex for the renderer that my python script is spending most of it's time drawing while the renderer is already done.  What you've given me has sped up the drawing a lot, but I'm hungry for more optimization!

There is no file format to be read.  The data is raw bytes and can be any format.

> Date: Thu, 15 May 2008 10:09:45 -0700
> From: gherron at islandtraining.com
> CC: python-list at python.org
> Subject: Re: How do I use the unpack function?
> 
> John Machin wrote:
> > On May 16, 2:11 am, Gary Herron <gher... at islandtraining.com> wrote:
> >   
> >> Marlin Rowley wrote:
> >>     
> >>> All:
> >>>       
> >>> I've got a script that runs really slow because I'm reading from a
> >>> stream a byte at a time:
> >>>       
> >>> // TERRIBLE
> >>> for y in range( height ):
> >>>         for color in range(4):
> >>>             for x in range( width ):
> >>>                 pixelComponent = fileIO.read(4)
> >>>                 buffer = unpack("!f",pixelComponent)  << unpacks ONE
> >>>       
> >
> > [snip]
> > Perhaps the OP might be able to use the Python Imaging Library (PIL)
> > instead of reinventing an image-file handler.
> >   
> 
> Indeed.  That's why my original answer included the line:
>     There are probably better ways overall, but this directly answers 
> your question.
> 
> Other possibilities.
> 
> I don't recognize the file format being read in here, but if it is a 
> standard image format, the PIL suggestion is a good way to go.
> 
> Or, if it is an image of not too enormous size, read the *whole* thing 
> in at once. 
> 
> Or rather than manipulate the array by carving off 4 bytes at a time, 
> just index through it in 4 byte chunks:
>   for i in range(width):
>       buffer = unpack("!f", pixelComponent[4*i:4*i+4])
> 
> Or
>   for i in range(0,4*width,4):
>       buffer = unpack("!f", pixelComponent[i:i+4])
> 
> Or
>   Use numpy.  Create an array of floats, and initialize it with the byte 
> string, making sure to take endianess int account.  (I'm quite sure this 
> could be made to work, and then the whole operation is enormously fast 
> with only several lines of Python code and *no* Python loops.
> 
> Or
>   ...?
> 
> Gary Herron
> 
> > --
> > http://mail.python.org/mailman/listinfo/python-list
> >   
> 
> --
> http://mail.python.org/mailman/listinfo/python-list

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