[Paraview] Add support for PARAVIEW_EXTRA_EXTERNAL_PLUGINS?

[John Biddiscombe]

Mike
> what is the difference between setting my Module as a 
> PARAVIEW_EXTRA_EXTERNAL_MODULES vs PARAVIEW_EXTRA_EXTERNAL_PLUGINS?

EXTERNAL_MODULES : the source files are added to the target for 
pvfilters. They might be static or dynamic, depending on how your build 
is configured. The code is compiled into pvfilters, the core of paraview.
CMake picks up the file 'NAME'ParaViewImport.cmake and uses it for the 
sources

EXTERNAL_PLUGINS : when BUILD_SHARED_LIBS is ON the source directory for 
each plugin is supplied and the MACRO "add_paraview_plugin" is called 
for each plugin listed passing the source directory in. The 
CmakeLists.txt file in the directory is used, just as if you were 
compiling the plugin separately. The plugin is added as a separate 
target to the paraview build, and appears just like all those 
overview/prism plugins that are gradually appearing in the build.

I develop custom plugins for several institutions (each one has 
different plugins), and each time I compile paraview for them, I then 
compile the plugins they need afterwards. Each time, they ask, "why 
can't you just compile the plugins at the same time as paraview". Well 
now I can. I could have used the EXTERNAL_MODULES feature as well, but 
as you have seen from emails on this list, there are Fluent, netCDF, 
OpenDX, blah vlah blah modules out there and many other people weant to 
use them too and expect to be able to compile the as plugins, not as 
internal modules. Plugins are in general easier to manage and I don't 
want to maintain multiple cmakelists files

Currently I have 3 setf for each module, and maintaining them is a pain.
1) compile as a vtk filter, (use cmakelists.txt)
2) compile as a plugin (use pv3-plugin/cmakelists.txt)
3) compiles as external_module into paraview (use 
'NAME'ParaViewImport.cmake)

too much work.
3) is no longer required by me.
2) is nice because changing a plugin is a quicker make than changing 
paraview source
2) also allows me to use my new external_plugins to compile at 
pv-compile time just like I used to with 3)

I hope this thread is finished now.

JB