Merge topic 'gltf_scene'

48eac350 GLTF document loader caches a default scene

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Reviewed-by: Alexy Pellegrini <alexy.pellegrini@kitware.com>
Reviewed-by: Dan Lipsa <dan.lipsa@kitware.com>
Merge-request: !11836

Documentation/release/dev/gltf-documentloader-scene.md

+## GLTF document loader default scene
+
+The `vtkGLTFDocumentLoader` ensures that the internal cache of scenes is non-empty for consumer code
+that have to rely on checking validity of the default scene.

IO/Geometry/vtkGLTFDocumentLoaderInternals.cxx

@@ -1473,6 +1473,12 @@ bool vtkGLTFDocumentLoaderInternals::LoadModelMetaData(
   if (!vtkGLTFUtils::GetIntValue(root, "scene", this->Self->GetInternalModel()->DefaultScene))
   {
     int nbScenes = static_cast<int>(this->Self->GetInternalModel()->Scenes.size());
+    if (nbScenes < 1)
+    {
+      // In case the file had no scenes, add an empty scene so that downstream code doesn't need to
+      // check that its default scene index is valid
+      this->Self->GetInternalModel()->Scenes.resize(1);
+    }
     if (this->Self->GetInternalModel()->DefaultScene < 0 ||
       this->Self->GetInternalModel()->DefaultScene >= nbScenes)
     {