From 5d02e0fe28860584646b25c94f07c7c0da996ece Mon Sep 17 00:00:00 2001
From: David Rowe <david@ctrlaltstudio.com>
Date: Sat, 29 Aug 2020 16:12:10 +1200
Subject: [PATCH] Fix blendshapes on planar meshes

---
 libraries/fbx/src/GLTFSerializer.cpp | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/libraries/fbx/src/GLTFSerializer.cpp b/libraries/fbx/src/GLTFSerializer.cpp
index 8d7688fcff..cd2e4e2720 100755
--- a/libraries/fbx/src/GLTFSerializer.cpp
+++ b/libraries/fbx/src/GLTFSerializer.cpp
@@ -1610,12 +1610,14 @@ bool GLTFSerializer::buildGeometry(HFMModel& hfmModel, const hifi::VariantHash&
                 }               
             }
 
-            // Add epsilon to mesh extents to compensate for planar meshes
-            mesh.meshExtents.minimum -= glm::vec3(EPSILON, EPSILON, EPSILON);
-            mesh.meshExtents.maximum += glm::vec3(EPSILON, EPSILON, EPSILON);
-            hfmModel.meshExtents.minimum -= glm::vec3(EPSILON, EPSILON, EPSILON);
-            hfmModel.meshExtents.maximum += glm::vec3(EPSILON, EPSILON, EPSILON);
-           
+            // Mesh extents must be at least minimum entity size, in particular for blendshapes to work on planar meshes.
+            const float ENTITY_ITEM_MIN_DIMENSION = 0.001f;
+            auto delta = glm::max(glm::vec3(ENTITY_ITEM_MIN_DIMENSION) - mesh.meshExtents.size(), glm::vec3(0.0f)) / 2.0f;
+            mesh.meshExtents.minimum -= delta;
+            mesh.meshExtents.maximum += delta;
+            hfmModel.meshExtents.minimum -= delta;
+            hfmModel.meshExtents.maximum += delta;
+
             mesh.meshIndex = hfmModel.meshes.size();
         }
         ++nodecount;