[Clam-devel] Ladspa Plugins using embeded Networks

[David García Garzón]

Network based ladspa plugins are already usable:
- The network is now embeded into the plugin so you are not limited to a 
single CLAM based plugin indicated by CLAM_NETWORK_PLUGIN_PATH.
- Metadata is not hardcoded but writen on user code. (id, label, name, maker, 
copyright).
- More than one network based plugin can be defined in a single dll

Take a look to the source code that a user should write to generate a plugin. 
I really like it :-)

https://iua-share.upf.edu/svn/clam/trunk/CLAM/examples/PluginExamples/ClamLadspaPluginExample/MyClamLadspaPlugin.cxx

The rest of code files in the folder are to be moved to CLAM core once the API 
is stable

Next step is generating them from the NetworkEditor ;-)


Some implementation details follow for those interested on how to embed data 
files in the executable.

At last i didn't use the hack i explained in my previous mail using ld or 
objcopy. It worked with programs, even i did some SCons tool to have them 
built and to rename the symbols as you want. But when i tried to link the 
generated object into a shared library, it complained about using different 
binary formats and i couldn't figure out how to change it.

I considered the following command i found on a mailing list:

(echo "const unsigned char binary_data[] = {"; od -txC datafile.xml | 
sed -e "s/^[0-9]*//" -e s"/ \([0-9a-f][0-9a-f]\)/0x\1,/g" -e"\$d" | 
sed -e"\$s/,$/};/") >myfile.c

Which generates c code representing the content of the file (i didn't believe 
either, try it). But it requires some tools such as 'od' and 'sed' that i 
don't know if they are present in all the platforms (specially windows). I 
discarded implementing that on python or in C if i found a better solution.

The final solution was using the GNU assembler directive .incfile which had 
the advantage of being able to name the symbol as you want. By using a 
parametrized macro i managed to make it very easy to include different files 
in code:

/// Include a given file as binary data
/// @arg varname is the variable that will hold the var (const char[])
/// @arg file is an absolute path or a relative path from the build point (not 
from the source file!!)
/// @todo Try to make CLAM_EXTERNAL_FILE_DATA work with path relatives to the 
source that uses the macro.
#define CLAM_EXTERNAL_FILE_DATA(varname, file) \
asm ( \
"  .section \".rodata\"\n" \
"   .type " #varname ", @object\n" \
" " #varname ":\n" \
"   .incbin \"" file "\"\n" \
"   .byte 0\n" \
"   .size " #varname ", .-" #varname "\n" \
); \
extern const char varname[]; \

This is used like this:
CLAM_EXTERNAL_FILE_DATA(myFile, "path/from/working/dir/file.clamnetwork")

The only drawback left for the solution to be perfect is that the file name 
must be relative to the working dir of the compilation, not relative to the 
source dir as it is logic. But gas is not that logic. In any case this seems 
a minor drawback.

David.