Re: [Openexr-devel] Changing the Header

[Florian Kainz]

Hi Barnaby,

every Header object has a "compression" attribute; you don't
have to insert a new one.  You can change the value of the
compression attribute like this:

    header.compression() = PXR24_COMPRESSION;

Your way of setting the attribute,

    header.insert ("compression", Imf::CompressionAttribute 
(Imf::PIZ_COMPRESSION));

should work, too.

Regarding the Visual C++ compiler warnings: the compiler is
right, you have to use /GR to enable run-time type information;
otherwise OpenEXR will not work.

According to a Visual C++ expert from LucasArts, /GR does not
degrade performance.  (Enabling run-time type information did
affect performance in VC6, but this was fixed in VC7.)

Florian



Barnaby Robson wrote:
> I noticed how easy it is to get the compression attribute from the 
> header with
> the Imf::Header function compression() but there seems to be an issue 
> when setting compression
> in a pre-existing header.
>  
> I am using the insert function like so to set Piz Compression (which, by 
> the way, is amazing)
>  
> header.insert ("compression", Imf::CompressionAttribute 
> (Imf::PIZ_COMPRESSION));
>  
> which is really just shorthand for saying this ...
>  
> // const Imf::Compression comp = Imf::PIZ_COMPRESSION;
> // Imf::TypedAttribute<Imf::Compression> attr(comp);
> // header.insert("compression", attr);
>  
> if I type it either way I get a long warning in .NET about a dynamic cast
>  
> C:\dev\rd\libs\3rdparty\OpenEXR\vc\vc7\include\IlmImf\ImfAttribute.h(355) 
> : warning C4541: 'dynamic_cast' used on polymorphic type 
> 'Imf::Attribute' with /GR-; unpredictable behavior may result
> C:\dev\rd\libs\3rdparty\OpenEXR\vc\vc7\include\Imath\ImathVec.h(234) : 
> while compiling class-template member function 'const 
> Imf::TypedAttribute<T> *Imf::TypedAttribute<T>::cast(const 
> Imf::Attribute *)'
> with
> [
> T=Imf::Compression
> ]
> C:\Program Files\Microsoft Visual Studio .NET 
> 2003\Vc7\include\xstring(521) : while compiling class-template member 
> function 'Imf::TypedAttribute<T>::TypedAttribute(void)'
> with
> [
> T=Imf::Compression
> ]
> C:\Program Files\Microsoft Visual Studio .NET 
> 2003\Vc7\include\xmemory(156) : while compiling class-template member 
> function 'Imf::TypedAttribute<T>::~TypedAttribute(void)'
> with
> [
> T=Imf::Compression
> ]
> C:\dev\rd\libs\3rdparty\OpenEXR\vc\vc7\include\IlmImf\ImfCompressionAttribute.h(54) 
> : see reference to class template instantiation 'Imf::TypedAttribute<T>' 
> being compiled
> with
> [
> T=Imf::Compression
> ]
> -----------------------------------------
>  
> I can stop this warning by adding the /GR flag to my compiler. The 
> option (/GR) adds code to check object types at run time.
> I was worried that this might slow down the code though ..
>  
> What do you guys do and what do you suggest ?
>  
> Thanks
>  
> barnaby
>  
>  
>
>
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