glTF importer: fix shapekey import with negative weight

io_scene_gltf2/__init__.py

@@ -15,7 +15,7 @@
 bl_info = {
     'name': 'glTF 2.0 format',
     'author': 'Julien Duroure, Scurest, Norbert Nopper, Urs Hanselmann, Moritz Becher, Benjamin Schmithüsen, Jim Eckerlein, and many external contributors',
-    "version": (1, 6, 12),
+    "version": (1, 6, 13),
     'blender': (2, 91, 0),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/imp/gltf2_blender_animation_weight.py

@@ -83,3 +83,10 @@ class BlenderWeightAnim():
                     group_name="ShapeKeys",
                     interpolation=animation.samplers[channel.sampler].interpolation,
                 )
+
+                # Expand weight range if needed
+                kb = obj.data.shape_keys.key_blocks[kb_name]
+                min_weight = min(coords[1:2])
+                max_weight = max(coords[1:2])
+                if min_weight < kb.slider_min: kb.slider_min = min_weight
+                if max_weight > kb.slider_max: kb.slider_max = max_weight

io_scene_gltf2/blender/imp/gltf2_blender_node.py

@@ -225,7 +225,11 @@ class BlenderNode():
         weights = pynode.weights or pymesh.weights or []
         for i, weight in enumerate(weights):
             if pymesh.shapekey_names[i] is not None:
-                obj.data.shape_keys.key_blocks[pymesh.shapekey_names[i]].value = weight
+                kb = obj.data.shape_keys.key_blocks[pymesh.shapekey_names[i]]
+                # extend range if needed
+                if weight < kb.slider_min: kb.slider_min = weight
+                if weight > kb.slider_max: kb.slider_max = weight
+                kb.value = weight
 
     @staticmethod
     def setup_skinning(gltf, pynode, obj):