Use shorts for triangle indices when possible for isosurface glTF exp…

…orts.

glue_ar/common/marching_cubes.py

@@ -11,7 +11,7 @@
 from glue_ar.common.stl_builder import STLBuilder
 from glue_ar.common.usd_builder import USDBuilder
 from glue_ar.common.volume_export_options import ARIsosurfaceExportOptions
-from glue_ar.gltf_utils import add_points_to_bytearray, add_triangles_to_bytearray, \
+from glue_ar.gltf_utils import SHORT_MAX, add_points_to_bytearray, add_triangles_to_bytearray, \
                                index_mins, index_maxes
 from glue_ar.utils import BoundsWithResolution, clip_sides, frb_for_layer, hex_to_components, isomin_for_layer, \
                           isomax_for_layer, layer_color
@@ -52,13 +52,15 @@ def add_isosurface_layer_gltf(builder: GLTFBuilder,
         add_points_to_bytearray(barr, points)
         point_len = len(barr)
 
-        add_triangles_to_bytearray(barr, triangles)
-        triangle_len = len(barr) - point_len
-
         pt_mins = index_mins(points)
         pt_maxes = index_maxes(points)
         tri_mins = [int(min(idx for tri in triangles for idx in tri))]
-        tri_maxes = [int(max(idx for tri in triangles for idx in tri))]
+        max_tri_index = int(max(idx for tri in triangles for idx in tri))
+        tri_maxes = [max_tri_index]
+
+        use_short = max_tri_index <= SHORT_MAX
+        add_triangles_to_bytearray(barr, triangles, short=use_short)
+        triangle_len = len(barr) - point_len
 
         builder.add_buffer(byte_length=len(barr), uri=level_bin)
 
@@ -83,9 +85,10 @@ def add_isosurface_layer_gltf(builder: GLTFBuilder,
             byte_offset=point_len,
             target=BufferTarget.ELEMENT_ARRAY_BUFFER,
         )
+        component_type = ComponentType.UNSIGNED_SHORT if use_short else ComponentType.UNSIGNED_INT
         builder.add_accessor(
             buffer_view=builder.buffer_view_count-1,
-            component_type=ComponentType.UNSIGNED_INT,
+            component_type=component_type,
             count=len(triangles)*3,
             type=AccessorType.SCALAR,
             mins=tri_mins,