Gui: Improve transform UI responsivness

This introduces much faster CenterOfMassProvider#supports method that
can be used as cheap pre-check to see if the object supplied could have
the center of mass and so delay the domputation to a moment where it is
actually needed.

src/App/Services.cpp

@@ -27,4 +27,9 @@ std::optional<Base::Vector3d>
 App::NullCenterOfMass::ofDocumentObject([[maybe_unused]] DocumentObject* object) const
 {
     return std::nullopt;
+}
+
+bool App::NullCenterOfMass::supports(DocumentObject* object) const
+{
+    return false;
 }

src/App/Services.h

@@ -55,6 +55,7 @@ class CenterOfMassProvider
 public:
     virtual ~CenterOfMassProvider() = default;
 
+    virtual bool supports(DocumentObject* object) const = 0;
     virtual std::optional<Base::Vector3d> ofDocumentObject(DocumentObject* object) const = 0;
 };
 
@@ -66,6 +67,7 @@ class NullCenterOfMass final : public CenterOfMassProvider
 {
 public:
     std::optional<Base::Vector3d> ofDocumentObject(DocumentObject* object) const override;
+    bool supports(DocumentObject* object) const override;
 };
 
 }

src/Gui/TaskTransform.cpp

@@ -173,7 +173,7 @@ void TaskTransform::loadPlacementModeItems() const
         QVariant::fromValue(PlacementMode::ObjectOrigin)
     );
 
-    if (centerOfMassProvider->ofDocumentObject(vp->getObject()).has_value()) {
+    if (centerOfMassProvider->supports(vp->getObject())) {
         ui->placementComboBox->addItem(
             tr("Center of mass / centroid"),
             QVariant::fromValue(PlacementMode::Centroid)

src/Mod/Part/App/Services.cpp

@@ -45,7 +45,7 @@ Base::Placement AttacherSubObjectPlacement::calculate(
 
 std::optional<Base::Vector3d> PartCenterOfMass::ofDocumentObject(App::DocumentObject* object) const
 {
-    if (const auto feature = dynamic_cast<Part::Feature*>(object)) {
+    if (const auto* feature = freecad_cast<Part::Feature*>(object)) {
         const auto shape = feature->Shape.getShape();
 
         if (const auto cog = shape.centerOfGravity()) {
@@ -57,3 +57,8 @@ std::optional<Base::Vector3d> PartCenterOfMass::ofDocumentObject(App::DocumentOb
 
     return {};
 }
+
+bool PartCenterOfMass::supports(App::DocumentObject* object) const
+{
+    return object->isDerivedFrom<Part::Feature>();
+}

src/Mod/Part/App/Services.h

@@ -42,6 +42,7 @@ class PartCenterOfMass final: public App::CenterOfMassProvider
 {
 public:
     std::optional<Base::Vector3d> ofDocumentObject(App::DocumentObject* object) const override;
+    bool supports(App::DocumentObject* object) const override;
 };
 
 #endif  // PART_SERVICES_H