Add DataOutBase::CompressionLevel::ascii

[peterrum]

closes #14277

The first commit reorders the code so that we have the structure #ifdef DEAL_II_WITH_ZLIB ... #else ... #endif comes and the second commit converts the #else to proper if-else statements.

FYI @mschreter

[drwells]

Nice feature - even though its not a zlib compression level it makes sense to put this here.

A few minor things:

1. We know what ASCII is but people newer to computing might not. Could you rename this to plain_text (or some similarly descriptive name) and define what that means in the enum?
2. Could you flip all the checks to do if (compression == plain_text) first instead of the opposite? That would highlight that plain text is the special case.
3. The docs for CompressionLevel need to be generalized to support a non-zlib case.

[peterrum]

We know what ASCII is but people newer to computing might not. Could you rename this to plain_text (or some similarly descriptive name) and define what that means in the enum?

The docs for CompressionLevel need to be generalized to support a non-zlib case.

Done 2x.

Could you flip all the checks to do if (compression == plain_text) first instead of the opposite? That would highlight that plain text is the special case.

I did it this way intentionally, since it allows me to use a single ifdef. In the other case, one needs to write two ifdef if I am not mistaken:

#ifdef DEAL_II_WITH_ZLIB
    if (flags.compression_level = DataOutBase::CompressionLevel::plain_text)
#endif
      {
        // plain text output
      }
#ifdef DEAL_II_WITH_ZLIB
    else
      {
        // binary output
      }
#endif

vs.

#ifdef DEAL_II_WITH_ZLIB
    if (flags.compression_level != DataOutBase::CompressionLevel::plain_text)
      {
        // binary output
      }
    else
#endif
      {
        // plain text output
      }

Personally, I prefer if I could keep it like this. Furthermore, this is also the format we use at other places, e.g., to switch between TBB and not-TBB implementations.

[drwells]

Yes, that makes sense!