Serialize/deserialize shader groups

[lgritz]

I'll introduce this set of changes by illustrating the "killer app":

$ myrenderer myscene.scene
...weird shader behavior or an error...

$ OSL_OPTIONS="archive_groupname=mygroup" myrenderer myscene.scene
$ ls mygroup*
mygroup.tar.gz
$ tar tf mygroup.tar.gz
shadergroup
a.oso
b.oso

This tar file contains a serialized description (in "shadergroup") of the shader group network -- shaders, instance parameter values, connections -- and the oso of every shader referenced by the group. These can be reconstituted to debug the shader from testshade or any other debugging-conducive environment, which does not have to be the original renderer.

This involves three parts:

Part 1:

Added a new variety of ShaderGroupBegin() that accepts a string containing "commands" that easily and human-readably describe the entire setup of a ShaderGroup, equivalent to a set of Parameter, Shader, and ConnectShaders calls. Here is an example:

ShaderGroupBegin ("groupname", "surface",
                      /*concatenated string follows: */
                      "param float fin 3.14; " 
                      "param float val 42.0 [[int lockgeom=0]]; " 
                      "shader a alayer;"
                      "shader b blayer;"
                      "connect alayer.f_out blayer.f_in;");

Added --group command to testshade so this can be tested and used from the
command line. Here's an example:

testshade -v -group "param float fin 3.14, shader a alayer, shader b blayer, connect alayer.f_out blayer.f_in"

(Commas are an allowed substitute for semicolons for statement separators, and the last statement separator is optional if it's at the end of the string; this makes it easier for command line use, where semicolons have special meaning in some contexts like our test scripts.)

Part 2:

The mirror image of this, where we can serialize (turn into a command string) an existing ShaderGroup. This is done by retrieving the group attribute "pickle":

std::string groupstring;
shadingsys->getattribute (groupptr, "pickle", groupstring);
std::cout << groupstring << "\n";

will print

param float fin 3.14 ; 
param float val 42.0 [[int lockgeom=0]] ; 
shader a alayer ;
shader b blayer ;
connect alayer.f_out blayer.f_in ;

Part 3:

shadingsys->archive_shadergroup(group,filename) will create an archive file (tar, tar.gz, or zip, depending on the file extension) containing a serialized description of the shader group as well as oso files for every shader referenced in the group.

Also, new ShadingSystem attributes "archive_groupname" and "archive_filename" will cause the named group to be automatically archived to the given filename, right after it is set up.

[lgritz]

Actually, I'm hoping to make it work on Windows, too. I just need somebody to tell me a reliable command line to invoke a zip'er. The rest of the file system manipulation ought to just work.

[fpsunflower]

I don't think there's any command line zipper built into windows. I think the only portable solution would require a third party library.

[lgritz]

Then the shell-out will fail at runtime. I'm tempted to leave it in, so that if they have a "tar" or "zip" implementation in the path, it will just work. Otherwise, it will simply make the directory, copy the files, fail the zip command, then wipe clean the directory, no harm no foul.