expose joint inverse bind matrices via method on FilamentInstance (#6388)

* expose joint inverse bind matrices via method on FilamentInstance

* change const pointer refs, add asserts and update release notes

Co-authored-by: Mathias Agopian <mathias@google.com>

RELEASE_NOTES.md

@@ -16,6 +16,7 @@ A new header is inserted each time a *tag* is created.
 - materials: `getNormalizedViewportCoord()` now returns the logical (i.e. user) viewport
              normalized position and keeps z reversed [⚠️ **Recompile Materials**]
 - backend: workaround Adreno shader compiler bug (#6355) [⚠️ **Recompile Materials**]
+- gltfio: expose joint inverse bind matrices via method on FilamentInstance
 - geometry: change computing tangent basis from normal vector to use Frisvad's method
 - filamesh: add error when uv coords size does not match num of vertices. (#6351)
 

libs/gltfio/include/gltfio/FilamentInstance.h

@@ -126,6 +126,13 @@ public:
      */
     void detachSkin(size_t skinIndex, utils::Entity target) noexcept;
 
+    /**
+     * Gets inverse bind matrices for all joints at the given skin index.
+     *
+     * See getJointCountAt for determining the number of matrices returned (i.e. the number of joints).
+     */
+    math::mat4f const* getInverseBindMatricesAt(size_t skinIndex) const;
+
     /**
      * Resets the AABB on all renderables by manually computing the bounding box.
      *

libs/gltfio/src/FFilamentInstance.h

@@ -117,6 +117,8 @@ struct FFilamentInstance : public FilamentInstance {
     const utils::Entity* getJointsAt(size_t skinIndex) const noexcept;
     void attachSkin(size_t skinIndex, utils::Entity target) noexcept;
     void detachSkin(size_t skinIndex, utils::Entity target) noexcept;
+    math::mat4f const* getInverseBindMatricesAt(size_t skinIndex) const;
+
     void recomputeBoundingBoxes();
 };
 

libs/gltfio/src/FilamentInstance.cpp

@@ -90,6 +90,12 @@ void FFilamentInstance::detachSkin(size_t skinIndex, Entity target) noexcept {
     mSkins[skinIndex].targets.erase(target);
 }
 
+mat4f const* FFilamentInstance::getInverseBindMatricesAt(size_t skinIndex) const {
+    assert_invariant(mOwner);
+    ASSERT_PRECONDITION(skinIndex < mOwner->mSkins.size(), "skinIndex must be less than the number of skins in this instance.");
+    return mOwner->mSkins[skinIndex].inverseBindMatrices.data();
+}
+
 void FFilamentInstance::recomputeBoundingBoxes() {
     ASSERT_PRECONDITION(mOwner->mSourceAsset,
             "Do not call releaseSourceData before recomputeBoundingBoxes");
@@ -415,6 +421,10 @@ void FilamentInstance::detachSkin(size_t skinIndex, Entity target) noexcept {
     return downcast(this)->detachSkin(skinIndex, target);
 }
 
+math::mat4f const* FilamentInstance::getInverseBindMatricesAt(size_t skinIndex) const {
+    return downcast(this)->getInverseBindMatricesAt(skinIndex);
+}
+
 void FilamentInstance::recomputeBoundingBoxes() {
     return downcast(this)->recomputeBoundingBoxes();
 }