Fix crash on missing weights data (#222)

lib/src/data_access/validate_accessors.dart

@@ -17,7 +17,6 @@
 library gltf.data_access.validate_accessors_data;
 
 import 'package:gltf/src/base/gltf_property.dart';
-import 'package:meta/meta.dart';
 
 Accessor<T> _guardAccessor<T extends num>(Accessor<T> accessor) {
   if (accessor == null) {
@@ -164,10 +163,7 @@ void validateAccessorsData(Gltf gltf, Context context) {
 
       // add a checker from the current primitive to the global list
       influencesCheckers.add(InfluencesChecker(context.getPointerString(),
-          jointsIterators: jointsIterators,
-          weightsIterators: weightsIterators,
-          maxJointIndex: maxJoints - 1,
-          limitingSkinIndex: limitingSkinIndex));
+          jointsIterators, weightsIterators, maxJoints - 1, limitingSkinIndex));
 
       context.path
         ..removeLast()
@@ -225,9 +221,7 @@ void _processAccessorElements(Context context) {
 
     for (final value in accessor.getElements()) {
       for (var t = 0; t < elementCheckers.length; t++) {
-        if (!elementCheckers[t].check(context, index, componentIndex, value)) {
-          continue;
-        }
+        elementCheckers[t].check(context, index, componentIndex, value);
       }
 
       if (++componentIndex == components) {
@@ -262,11 +256,8 @@ class InfluencesChecker {
   double _threshold = 0;
   final Set<int> _currentIndices = <int>{};
 
-  InfluencesChecker(this.path,
-      {@required this.jointsIterators,
-      @required this.weightsIterators,
-      @required this.maxJointIndex,
-      @required this.limitingSkinIndex})
+  InfluencesChecker(this.path, this.jointsIterators, this.weightsIterators,
+      this.maxJointIndex, this.limitingSkinIndex)
       : assert(jointsIterators.length == weightsIterators.length),
         assert(maxJointIndex >= 0),
         assert(limitingSkinIndex >= 0);
@@ -298,7 +289,12 @@ class InfluencesChecker {
       }
 
       final weight = weightsIterators[i].current;
-      assert(weight != null);
+
+      if (weight == null) {
+        // insufficient weights data
+        _done = true;
+        return;
+      }
 
       if (weight != 0) {
         var unique = true;

test/base/assets.json

@@ -241,7 +241,8 @@
             "index_buffer_primitive_restart.gltf": "Index buffer with primitive restart value",
             "normals_tangents_non_unit_invalid_sign.gltf": "Non-unit normals and tangents, invalid sign",
             "colors_non_clamped.gltf": "Non-clamped vertex colors",
-            "joints_weights_complex.gltf": "Complex joints/weights data check"
+            "joints_weights_complex.gltf": "Complex joints/weights data check",
+            "joints_no_weights.gltf": "Missing weights data"
         }
     },
     "node": {

test/base/data/mesh_data/joints_no_weights.gltf

@@ -0,0 +1,76 @@
+{
+    "asset": {
+        "version": "2.0"
+    },
+    "nodes": [
+        {},
+        {
+            "mesh": 0,
+            "skin": 0
+        }
+    ],
+    "skins": [
+        {
+            "joints": [0]
+        }
+    ],
+    "meshes": [
+        {
+            "primitives": [
+                {
+                    "attributes": {
+                        "POSITION": 0,
+                        "JOINTS_0": 1,
+                        "WEIGHTS_0": 2
+                    },
+                    "mode": 0
+                }
+            ]
+        }
+    ],
+    "accessors": [
+        {
+            "type": "VEC3",
+            "componentType": 5126,
+            "count": 1,
+            "min": [
+                -1.0,
+                -1.0,
+                -1.0
+            ],
+            "max": [
+                1.0,
+                1.0,
+                1.0
+            ]
+        },
+        {
+            "type": "VEC4",
+            "componentType": 5121,
+            "count": 1,
+            "bufferView": 0,
+            "byteOffset": 12
+        },
+        {
+            "type": "VEC4",
+            "componentType": 5126,
+            "count": 1,
+            "bufferView": 0,
+            "byteOffset": 16
+        }
+    ],
+    "bufferViews": [
+        {
+            "buffer": 0,
+            "byteLength": 32,
+            "byteStride": 32,
+            "target": 34962
+        }
+    ],
+    "buffers": [
+        {
+            "byteLength": 16,
+            "uri": "data:application/octet-stream;base64,AAAAAAAAAAAAAAAAAAAAAA=="
+        }
+    ]
+}

test/base/data/mesh_data/joints_no_weights.gltf.report.json

@@ -0,0 +1,49 @@
+{
+    "uri": "test/base/data/mesh_data/joints_no_weights.gltf",
+    "mimeType": "model/gltf+json",
+    "validatorVersion": "2.0.0-dev.3.10",
+    "issues": {
+        "numErrors": 1,
+        "numWarnings": 0,
+        "numInfos": 1,
+        "numHints": 0,
+        "messages": [
+            {
+                "code": "BUFFER_VIEW_TOO_LONG",
+                "message": "BufferView does not fit buffer (0) byteLength (16).",
+                "severity": 0,
+                "pointer": "/bufferViews/0/byteLength"
+            },
+            {
+                "code": "UNUSED_OBJECT",
+                "message": "This object may be unused.",
+                "severity": 2,
+                "pointer": "/nodes/1"
+            }
+        ],
+        "truncated": false
+    },
+    "info": {
+        "version": "2.0",
+        "resources": [
+            {
+                "pointer": "/buffers/0",
+                "mimeType": "application/gltf-buffer",
+                "storage": "data-uri",
+                "byteLength": 16
+            }
+        ],
+        "animationCount": 0,
+        "materialCount": 0,
+        "hasMorphTargets": false,
+        "hasSkins": true,
+        "hasTextures": false,
+        "hasDefaultScene": false,
+        "drawCallCount": 1,
+        "totalVertexCount": 1,
+        "totalTriangleCount": 0,
+        "maxUVs": 0,
+        "maxInfluences": 4,
+        "maxAttributes": 3
+    }
+}