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Re: [MPlayer-dev-eng] [PATCH] MNG detection fails with libjpeg-turbo




On 2017-11-26 at 15:36, The Wanderer wrote:

> With current SVN (and for as long as I can remember checking), the
> configure check for the availability of libmng fails. Today I finally
> got around to looking into why.
> 
> 
> The test performs a compile check against libmng.h, which includes
> jpeglib.h. With libjpeg-turbo (the source of jpeglib.h in current
> Debian), this test fails because FILE is undefined. This is typedef is
> normally expected to come from stdio.h.
> 
> https://github.com/libjpeg-turbo/libjpeg-turbo/issues/17
> indicates that this is intentional, for backwards compatibility with
> libjpeg, and that "it is actually a design requirement of the libjpeg
> API that you include stdio.h before including jpeglib.h.".
> 
> This would seem to indicate that this has been broken for a very long
> time, and quite possibly no one noticed (which would imply that no one
> bothered trying to compile with MNG support). The last MNG-related
> commits seem to have been in 2012; support was originally added in 2011.
> 
> 
> The compilation check is performed by the return_statement_check
> function, which only permits passing one header-file argument. There is
> an existing statement_check_broken function, specifically for use with
> headers which don't include some of their own dependencies; however, it
> hardcodes a 'return 0', whereas return_statement_check permits passing
> in an expression to be used in the return statement.
> 
> Rather than try to add an ' 0' to all callers of statement_check_broken,
> I've duplicated it into return_statement_check_broken, which adds the
> return-statement argument from return_statement_check.
> 
> With that, detection of libmng succeeds. With an include of stdio.h
> added to vo_mng.c, compilation also succeeds.

And, just for the record, the result of compilation does appear to work;
playing a file with 'vo mng:output=/path/to/file.mng' causes the file to
be created (though only when the player exits, for some reason), and the
resulting file can be played back.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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