Re: [boost] [gil] New IO release

Subject: Re: [boost] [gil] New IO release
From: Domagoj Saric (dsaritz_at_[hidden])
Date: 2010-11-30 17:23:35

"Christian Henning" <chhenning_at_[hidden]> wrote in message 
news:AANLkTimfZVaObSw=2pCxFEJp4AkMbYbq1jXXLej=QC8m_at_mail.gmail.com...

> io_new is also object-oriented but it also provides, as you know, the
> free floating helper functions like read_image, etc. Even though, I
> don't state it in the documentation but you could use the underlying
> classes also. All image formats use the same reader class which is
> hidden inside the detail namespace. For instance:
>
> [taken from image_read.hpp]
>
> detail::reader< Device
>              , FormatTag
>              , detail::read_and_no_convert
>              > reader( file
>                      , settings
>                      );
>
> reader.init_image( img
>                 , reader.get_info()
>                 );
>
> reader.apply( view( img ));
>
> This object can be reused at will.

Isn't it the other way around, the free functions are the official interface 
while the detail::reader<> class template is the helper implementation 
detail..?
And the reader objects, AFAICT, cannot actually be reused in a meaningful 
way (e.g. the apply<>() method for the JPEG reader calls 
jpeg_start_decompress() and jpeg_finish_decompress() ) ...

> But I have a question for you. Are
> you sure you can easily reuse a jpeg_decompress_struct object and jump
> around a jpeg image without getting it confused? I mean, for instance,
> imagine you read the last image line first and then try to read the
> first line. Does that work?

With LibJPEG, you cannot 'jump around easily' (e.g. to go back/rewind the 
decoding you have to abort and restart the decompression) but 'jumping 
around' does not really represent a significant use case (io2 does however 
detect this and automatically handles it)...'Forward/single direction' 
reading OTOH is a different story as the io2 reader preserves the 
decompression state so that you can simply and cheaply resume reading a JPEG 
(e.g. for sequential ROI based access)...

> I would love to work with you to create the best image reader/writer
> possible for the boost community. Let's see what the review brings to
> the table and afterwards we can start sorting out the major
> differences. How does that sound?

Well if the change is already inevitable or very probable, a full official 
review of a library that is going to change (or at least a significant part 
of it) in a significant way both from within and without might be 
misplaced...But the review date is here so let's make the best of it :)
I'll find some time to reiterate in short the objections from my original 
post in the official review thread...

-- 
"What Huxley teaches is that in the age of advanced technology, spiritual
devastation is more likely to come from an enemy with a smiling face than
from one whose countenance exudes suspicion and hate."
Neil Postman