add sandbox dir with a metaball demo animation script

sandbox dir is intended to be a space for unmanaged uninstalled demonstration scripts.  ideally helpful snippets that show how to create geometry, chain commands together, achieve some interesting result without the overhead of docs.  sort of like proc-db but higher-level cli demos.

sh/CMakeLists.txt

@@ -35,6 +35,7 @@ set(noinst_SCRIPTS
   news2tracker.sh
   template.sh
   ws.sh
+  sandbox/metaring.sh
   )
 CMAKEFILES(${sh_SCRIPTS})
 CMAKEFILES(${noinst_SCRIPTS})

sh/sandbox/metaring.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+# set up a half-torus ring
+echo " put tor tor V {0 0 0}  H {1 0 0}  r_a 400 r_h 100 ;
+       put sph ell V {0 400 0}  A {100 0 0}  B {0 100 0}  C {0 0 100} ;
+       put sph2 ell V {0 -400 0}  A {100 0 0}  B {0 100 0}  C {0 0 100} ;
+       in cut rpp -101 101 -501 501 -501 0 ;
+       r ring.r u tor - cut u sph u sph2 ;" | mged -c metaring.g
+
+# create metaballs at all positions
+for i in `seq 0 5 350` ; do c=`echo "scale=10; c($i * 4*a(1) / 180) * 400" | bc -l` ; s=`echo "scale=10; s($i * 4*a(1) / 180) * 400" | bc -l` ; echo "kill metaball`printf %03d $i` ; in metaball`printf %03d $i` metaball 0 1 3 0 400 0 100 0 -400 0 100 0 $c $s 100" ; done | mged -c metaring.g
+
+# render image frames
+for i in `seq 0 5 350` ; do echo $i ;  rm -f m`printf %03d $i`.png ; rt -o m`printf %03d $i`.png -c "viewsize 1200" -c "orientation .5 .5 .5 .5" -c "eye_pt 5000 0 0" metaring.g metaball`printf %03d $i` ring.r 2>/dev/null ; done
+
+# convert frames to animation
+convert *.png anim.gif
+