Add methods to UsdStage for saving edited layers

(Internal change: 1727839)

pxr/usd/lib/usd/stage.cpp

@@ -2766,6 +2766,62 @@ UsdStage::IsSupportedFile(const std::string& filePath)
                                           UsdUsdFileFormatTokens->Target);
 }
 
+namespace {
+
+void _SaveLayers(const SdfLayerHandleVector& layers)
+{
+    for (const SdfLayerHandle& layer : layers) {
+        if (!layer->IsDirty()) {
+            continue;
+        }
+
+        if (layer->IsAnonymous()) {
+            TF_WARN("Not saving @%s@ because it is an anonymous layer",
+                    layer->GetIdentifier().c_str());
+            continue;
+        }
+
+        // Sdf will emit errors if there are any problems with
+        // saving the layer.
+        layer->Save();
+    }
+}
+
+}
+
+void
+UsdStage::Save()
+{
+    SdfLayerHandleVector layers = GetUsedLayers();
+
+    const PcpLayerStackPtr localLayerStack = _GetPcpCache()->GetLayerStack();
+    if (TF_VERIFY(localLayerStack)) {
+        const SdfLayerHandleVector sessionLayers = 
+            localLayerStack->GetSessionLayers();
+        const auto isSessionLayer = 
+            [&sessionLayers](const SdfLayerHandle& l) {
+                return std::find(
+                    sessionLayers.begin(), sessionLayers.end(), l) 
+                    != sessionLayers.end();
+            };
+
+        layers.erase(std::remove_if(layers.begin(), layers.end(), 
+                                    isSessionLayer),
+                     layers.end());
+    }
+
+    _SaveLayers(layers);
+}
+
+void
+UsdStage::SaveSessionLayers()
+{
+    const PcpLayerStackPtr localLayerStack = _GetPcpCache()->GetLayerStack();
+    if (TF_VERIFY(localLayerStack)) {
+        _SaveLayers(localLayerStack->GetSessionLayers());
+    }
+}
+
 static bool
 _CheckAbsolutePrimPath(const SdfPath &path)
 {

pxr/usd/lib/usd/stage.h

@@ -414,6 +414,38 @@ class UsdStage : public TfRefBase, public TfWeakBase {
 
     /// @}
 
+    // --------------------------------------------------------------------- //
+    /// \anchor Usd_layerSerialization
+    /// \name Layer Serialization
+    ///
+    /// Functions for saving changes to layers that contribute opinions to
+    /// this stage.  Layers may also be saved by calling SdfLayer::Save or
+    /// exported to a new file by calling SdfLayer::Export.
+    ///
+    /// @{
+
+    /// Calls SdfLayer::Save on all dirty layers contributing to this stage
+    /// except session layers and sublayers of session layers.
+    ///
+    /// This function will emit a warning and skip each dirty anonymous
+    /// layer it encounters, since anonymous layers cannot be saved with
+    /// SdfLayer::Save. These layers must be manually exported by calling
+    /// SdfLayer::Export.
+    USD_API
+    void Save();
+
+    /// Calls SdfLayer::Save on all dirty session layers and sublayers of 
+    /// session layers contributing to this stage.
+    ///
+    /// This function will emit a warning and skip each dirty anonymous
+    /// layer it encounters, since anonymous layers cannot be saved with
+    /// SdfLayer::Save. These layers must be manually exported by calling
+    /// SdfLayer::Export.
+    USD_API
+    void SaveSessionLayers();
+
+    /// @}
+
     // --------------------------------------------------------------------- //
     /// \anchor Usd_variantManagement
     /// \name Variant Management

pxr/usd/lib/usd/wrapStage.cpp

@@ -336,6 +336,9 @@ void wrapUsdStage()
         .def("Close", &UsdStage::Close)
         .def("Reload", &UsdStage::Reload)
 
+        .def("Save", &UsdStage::Save)
+        .def("SaveSessionLayers", &UsdStage::SaveSessionLayers)
+
         .def("GetGlobalVariantFallbacks",
              &UsdStage::GetGlobalVariantFallbacks,
              return_value_policy<TfPyMapToDictionary>())