Enable building E57Format as a shared library

[asmaloney]

No description provided.

[asmaloney]

@pscamodio could you please try this to see if it works for you?

The main differences from your PR are:

• It doesn't set BUILD_SHARED_LIBS as an option, but it will respect it. (I don't like libraries polluting the cmake option-space.)
• It uses GenerateExportHeader instead of hand-coding the include. This will generate the appropriate include based on the platform (__attribute__((visibility("hidden"))), etc.).

[pscamodio]

Hi asmaloney
I'm testing this version of the lib and it seem to work.
But there's one problem with the cmake install
Currently if you build a shared library the .dll file is not installed
You need to add
RUNTIME DESTINATION bin to the install(TARGET call

install(
    TARGETS
        E57Format
    EXPORT
        E57Format-export
    ARCHIVE DESTINATION lib
+ ARCHIVE DESTINATION bin
)

[pscamodio]

Thank you.
Everything works now.
Your library was the only reason for me to keep xerces around in my codebase.
Now I can package your library as a dll with xerces statically compiled inside and remove one public dependency from my tree.
Thank you

[asmaloney]

Thanks for prompting this change with your PR @pscamodio!

I would love to eliminate Xerces, but it's so embedded in this code it's not easy. I started to do it, but it really needs a rewrite.

[Jean-Roc]

@asmaloney just found out this PR, you are mentioning getting ride of xerces, it seems the PDAL crew did it with their fork
https://github.com/PDAL/PDAL/commits/master/plugins/e57/libE57Format

[asmaloney]

@Jean-Roc Thanks. I didn't realize they forked my fork. I took a look at their history and I don't see where they replaced xerces.

Where did you see it - on a branch? What did they replace it with?

[Jean-Roc]

You are right, I made a mistake. I was trying to understand some differences in e57 handling between CC and pdal, found in their initial PR a mention of switching to libxml2, read the wrong cmakelist. Sorry for the noise

[asmaloney]

No problem. I wish they hadn't forked the fork though 😄 There are few enough people doing this that it would be nice to keep any fixes in one place so everyone can benefit. 🤷‍♂️