Re: [boost] [gil::io] Feedback for scanline_read_iterator

Subject: Re: [boost] [gil::io] Feedback for scanline_read_iterator
From: Christian Henning (chhenning_at_[hidden])
Date: 2013-02-19 20:39:03

Hi Phil,

> PSEUDO-CODE!!!!
>
>
> class iterator {
>   buffer_t& buffer;
>   size_t pending_advance_rows;
>
> public:
>   const buffer_t& operator*() {
>     while (pending_advance_rows > 1) {
>       format_specific_skip_row();
>       --pending_advance_rows;
>     }
>     if (pending_advance_rows == 1) {
>       format_specific_read_row_into(buffer);
>       --pending_advance_rows;
>     }
>     return buffer;
>   }
>
>   void operator++() {
>     ++pending_advance_rows;
>   }
> };
>

I think the scanline_read_iterator is a little more complicated. I
have uploaded the lateted "iteration" here:

http://svn.boost.org/svn/boost/trunk/boost/gil/extension/io/detail/scanline_read_iterator.hpp

It's crucial that the reader's "read" and "skip" functions are called
appropriately. These two functions behave very differently for
different image formats.
For instance two calls to operator* should not result in two reads. Or
when a user does std::advance( it, 20 ) the iterator needs to call
"skip" 20 times without any "reads".

Jeffery suggested to use two booleans to get the order of calls
correct. Let's hope I got it right this time.

Thanks,
Christian