Haven't talked to Alan in at least a month or so. I remember reading a
post of his, though, on the MR list that sounded like he was about to do
something really cool with geometry shaders.
I'm sure you've already probably found it, since you breath XSIBase
threads instead of air, but, the relevant link is:
http://www.xsibase.com/forum/index.php?board=14;action=display;threadid=11925;start=3
On that page, there's a link to Daniel's shader with source and Sascha
Robitzki's similar shader with no source, I think. Also, there's
another thread at
http://www.xsibase.com/forum/index.php?board=14;action=display;threadid=21845;start=0
where someone named samy_m has provided source for a shader that
supposedly copies the material list from the original object like
Sascha's shader. Haven't checked that one out. If it doesn't work,
there was a post a while back (which I'm including below) on the MR list
about two slightly incorrect ways to copy the material list for the new
instance. I'm not sure if it's fixed in instancer_v2 or not, but
Daniel's original shader also didn't loop through all the objects
referenced by the geometry shader, so you could only do one object with
it. That's a really easy fix, though.
I believe all of these shaders require an existing object in XSI.
Here's a link to lamrug's procedural feather placeholder shader, which I
think could be used as a starting point for all sorts of useful geometry
shaders:
http://www.lamrug.org/resources/geohairtips2.html
and second, here's the post I mentioned above from Gonzalo Garramuno (to
Alan, I think). Neither of his two methods for copying a material list
(for when you have cluster materials) worked for me, but I did get a
modified version of the second method to work. If I recall, it was
actually simpler than the original code:
It's rather straightforward, if you dig a little in geoshader.h.
----------------- Sample untested code ------------------
miTag objTag;
mi_query( miQ_INST_ITEM, state, instanceTag, &objTag );
assert( objTag != miNULLTAG );
// Get original instance pointer
miInstance* iorig = (miInstance*) mi_db_access( instanceTag );
// Get name of object - should not be run in multihost environment
const char* objName = mi_api_tag_lookup( objTag );
assert( objName != NULL );
// Make sure we are not in incremental mode
mi_api_incremental( miFALSE );
// Create new instance
miInstance* i = mi_api_instance_begin( mi_mem_strdup("somenewname") );
//
// Get and copy material(s)
//
i->material = iorig->material;
assert( i->material != miNULLTAG );
// I think the above is enough to copy all the materials, as I
believe several
// instances can share the same taglist when multiple materials are
used.
// If not, do this:
#if 0
miTag m = iorig->material;
if ( iorig->mtl_array_size > 0 ) // or maybe 1, not sure.
{
miDlist* origd = (miDlist*) mi_db_access( m );
assert( origd != NULL );
// Some sanity checks...
assert( origd->type == miDLIST_TAG );
assert( origd->nb == iorig->mtl_array_size );
// Create new list...
miDlist* d = mi_api_dlist_create( miDLIST_TAG );
// Copy list to new instance...
int numMaterials = iorig->mtl_array_size;
i->mtl_array_size = numMaterials;
for ( int j = 0; j < numMaterials; ++j )
{
m = ((miTag*) origd->dlist)[j];
assert( m != miNULLTAG );
mi_api_dlist_add( d, &m );
}
// Obtain a tag from list
m = mi_api_taglist( d );
// After that, the temp dlist can be removed
mi_api_dlist_delete( d );
// Unpin original reference to material list
mi_db_unpin( iorig->material ); origd = NULL;
assert( m != miNULLTAG );
}
i->material = m;
#endif
// Fill Matrix i->tf.global_to_local here.
// Create inverse matrix
mi_matrix_invert( i->tf.local_to_global, i->tf.global_to_local );
// we are done with instance
miTag newTag = mi_api_instance_end( mi_mem_strdup(objName),
miNULLTAG, miNULLTAG );
// Make sure to unpin the original reference to instance
mi_db_unpin( instanceTag ); iorig = NULL;
// Add new tag as a geoshader result. This makes sure that new
instance will
// get added to the instgroup render list.
mi_geoshader_add_result(result, newTag, 0, 0);
// And you are done... there should now be a new instance in your
scene...
--
Gonzalo Garramuno
"Great, Max and Maya got hitched, and now they're gonna have a geeky
kid named Marvin."
-- someone at cgtalk
Bernard Lebel wrote:
Andy, have you spoke to Alan today or what? :-)
In fact the mr doc has a paragraph on geometry shader place-holders.
But I'm affraid that this feature is quite far from my reach. I'm not
much further past the "hello world" exercice, so geometry shaders may
not come soon. But I'd be interested in that shader of bigMuh, I'll
definitely check it out. I used RIB archives in Maya, and I must say
it was quite remarkable, I wouldn't mind having such functionality in
XSI......
Cheers
Bernard
On 5/23/06, Andy Jones <andy(at)thefront.com> wrote:
Incidentally, have you tried using a geometry shader for instancing
instead of particles? Seems like a good way to minimize XSI's overhead
to a single object without having to load any additional real geometry
(aside from the freaked out cube icon) into XSI's memory. Plus, you can
shade the geometry shaders individually to get more per-instance
effects. There was a theBigMuh shader posted on a thread a while back
on XSIBase. Somewhere, I also saw a version that obeyed the original
materials of the object, which is what I assume most people would want.
I'd guess it's heavier than particles, but maybe it's a little easier to
manage.
-Andy
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