Implements System<T>::ExecuteInitializationEvents()

and uses it in MeshcatPoseSliders() and JointSliders()

bindings/pydrake/systems/framework_py_systems.cc

@@ -410,6 +410,9 @@ struct Impl {
         .def("CalcForcedUnrestrictedUpdate",
             &System<T>::CalcForcedUnrestrictedUpdate, py::arg("context"),
             py::arg("state"), doc.System.CalcForcedUnrestrictedUpdate.doc)
+        .def("ExecuteInitializationEvents",
+            &System<T>::ExecuteInitializationEvents, py::arg("context"),
+            doc.System.ExecuteInitializationEvents.doc)
         .def("GetUniquePeriodicDiscreteUpdateAttribute",
             &System<T>::GetUniquePeriodicDiscreteUpdateAttribute,
             doc.System.GetUniquePeriodicDiscreteUpdateAttribute.doc)

bindings/pydrake/systems/test/custom_test.py

@@ -638,6 +638,27 @@ def _system_reset(self, system, context, event, state):
         self.assertTrue(system.called_reset)
         self.assertTrue(system.called_system_reset)
 
+        # Test ExecuteInitializationEvents.
+        system = TrivialSystem()
+        context = system.CreateDefaultContext()
+        system.ExecuteInitializationEvents(context=context)
+        self.assertFalse(system.called_per_step)
+        self.assertFalse(system.called_periodic)
+        self.assertTrue(system.called_initialize_publish)
+        self.assertTrue(system.called_initialize_discrete)
+        self.assertTrue(system.called_initialize_unrestricted)
+        self.assertFalse(system.called_periodic_publish)
+        self.assertFalse(system.called_periodic_discrete)
+        self.assertFalse(system.called_periodic_unrestricted)
+        self.assertFalse(system.called_per_step_publish)
+        self.assertFalse(system.called_per_step_discrete)
+        self.assertFalse(system.called_per_step_unrestricted)
+        self.assertFalse(system.called_getwitness)
+        self.assertFalse(system.called_witness)
+        self.assertFalse(system.called_guard)
+        self.assertFalse(system.called_reset)
+        self.assertFalse(system.called_system_reset)
+
     def test_event_handler_returns_none(self):
         """Checks that a Python event handler callback function is allowed to
         (implicitly) return None, instead of an EventStatus. Because of all the

multibody/meshcat/BUILD.bazel

@@ -104,6 +104,7 @@ drake_cc_googletest(
         "//geometry:meshcat_visualizer",
         "//geometry/test_utilities:meshcat_environment",
         "//multibody/parsing",
+        "//systems/framework/test_utilities",
     ],
 )
 

multibody/meshcat/joint_sliders.cc

@@ -279,6 +279,8 @@ Eigen::VectorXd JointSliders<T>::Run(const Diagram<T>& diagram,
   using Duration = std::chrono::duration<double>;
   const auto start_time = Clock::now();
 
+  diagram.ExecuteInitializationEvents(root_context.get());
+
   // Set the context to the initial slider values.
   plant_->SetPositions(&plant_context,
                        this->get_output_port().Eval(sliders_context));

multibody/meshcat/joint_sliders.h

@@ -120,9 +120,12 @@ class JointSliders final : public systems::LeafSystem<T> {
   value of the plant Context.
 
   @pre `diagram` must be a top-level (i.e., "root") diagram.
-  @pre `diagram` must contain this JointSliders system.
   @pre `diagram` must contain the `plant` that was passed into this
   JointSliders system's constructor.
+  @pre `diagram` must contain this JointSliders system, however the output of
+  these sliders need not be connected (even indirectly) to any `plant` input
+  port. The positions of the `plant` will be updated directly using a call to
+  `plant.SetPositions(...)` when the slider values change.
   */
   Eigen::VectorXd Run(const systems::Diagram<T>& diagram,
                       std::optional<double> timeout = std::nullopt,

multibody/meshcat/test/joint_sliders_test.cc

@@ -10,6 +10,7 @@
 #include "drake/multibody/parsing/parser.h"
 #include "drake/multibody/plant/multibody_plant.h"
 #include "drake/systems/framework/diagram_builder.h"
+#include "drake/systems/framework/test_utilities/initialization_test_system.h"
 
 namespace drake {
 namespace multibody {
@@ -282,13 +283,21 @@ TEST_F(JointSlidersTest, Run) {
   MeshcatVisualizer<double>::AddToBuilder(&builder_, scene_graph_, meshcat_);
   auto* dut = builder_.AddSystem<JointSliders<double>>(meshcat_, &plant_,
                                                        initial_value);
+
+  auto init_system = builder_.AddSystem<systems::InitializationTestSystem>();
+
   auto diagram = builder_.Build();
 
   // Run for a while.
   const double timeout = 1.0;
   Eigen::VectorXd q = dut->Run(*diagram, timeout);
   EXPECT_TRUE(CompareMatrices(q, initial_value));
 
+  // Confirm that initialization events were triggered.
+  EXPECT_TRUE(init_system->get_pub_init());
+  EXPECT_TRUE(init_system->get_dis_update_init());
+  EXPECT_TRUE(init_system->get_unres_update_init());
+
   // Note: the stop button is deleted on timeout, so we cannot easily check
   // that it was created correctly here.
 

systems/framework/BUILD.bazel

@@ -734,7 +734,8 @@ drake_cc_googletest(
         "//common:essential",
         "//common/test_utilities:expect_no_throw",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -746,7 +747,8 @@ drake_cc_googletest(
         "//common:essential",
         "//common/test_utilities:expect_no_throw",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -803,7 +805,9 @@ drake_cc_googletest(
         "//common/test_utilities:is_dynamic_castable",
         "//examples/pendulum:pendulum_plant",
         "//systems/analysis/test_utilities:stateless_system",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:initialization_test_system",
+        "//systems/framework/test_utilities:pack_value",
+        "//systems/framework/test_utilities:scalar_conversion",
         "//systems/primitives:adder",
         "//systems/primitives:constant_value_source",
         "//systems/primitives:constant_vector_source",
@@ -822,7 +826,7 @@ drake_cc_googletest(
         "//common/test_utilities:eigen_matrix_compare",
         "//common/test_utilities:expect_throws_message",
         "//common/test_utilities:is_dynamic_castable",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -863,7 +867,7 @@ drake_cc_googletest(
         ":leaf_context",
         "//common:essential",
         "//common/test_utilities",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -874,7 +878,9 @@ drake_cc_googletest(
         "//common:essential",
         "//common/test_utilities",
         "//common/test_utilities:limit_malloc",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:initialization_test_system",
+        "//systems/framework/test_utilities:my_vector",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -889,7 +895,7 @@ drake_cc_googletest(
     name = "model_values_test",
     deps = [
         ":model_values",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -898,7 +904,7 @@ drake_cc_googletest(
     deps = [
         ":abstract_values",
         "//common:essential",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -907,7 +913,7 @@ drake_cc_googletest(
     deps = [
         ":parameters",
         "//common:essential",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:pack_value",
     ],
 )
 
@@ -941,7 +947,8 @@ drake_cc_googletest(
     deps = [
         ":system_output",
         "//common:essential",
-        "//systems/framework/test_utilities",
+        "//common/test_utilities:is_dynamic_castable",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -972,7 +979,7 @@ drake_cc_googletest(
         ":input_port",
         ":leaf_system",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -984,7 +991,7 @@ drake_cc_googletest(
         "//common:essential",
         "//common/test_utilities:expect_no_throw",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
         "//systems/primitives:constant_vector_source",
     ],
 )
@@ -1011,7 +1018,7 @@ drake_cc_googletest(
         "//common:unused",
         "//common/test_utilities:expect_no_throw",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -1030,7 +1037,7 @@ drake_cc_googletest(
         "//common:essential",
         "//common:unused",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:my_vector",
     ],
 )
 
@@ -1048,7 +1055,7 @@ drake_cc_googletest(
     name = "single_output_vector_source_test",
     deps = [
         ":single_output_vector_source",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:scalar_conversion",
     ],
 )
 
@@ -1058,7 +1065,7 @@ drake_cc_googletest(
         ":vector_system",
         "//common/test_utilities:expect_no_throw",
         "//common/test_utilities:expect_throws_message",
-        "//systems/framework/test_utilities",
+        "//systems/framework/test_utilities:scalar_conversion",
         "//systems/primitives:integrator",
     ],
 )

systems/framework/system.cc

@@ -478,6 +478,37 @@ void System<T>::GetInitializationEvents(
   DoGetInitializationEvents(context, events);
 }
 
+template <typename T>
+void System<T>::ExecuteInitializationEvents(Context<T>* context) const {
+  auto discrete_updates = AllocateDiscreteVariables();
+  auto state = context->CloneState();
+  auto init_events = AllocateCompositeEventCollection();
+
+  // NOTE: The execution order here must match the code in
+  // Simulator::Initialize().
+  GetInitializationEvents(*context, init_events.get());
+  // Do unrestricted updates first.
+  if (init_events->get_unrestricted_update_events().HasEvents()) {
+    CalcUnrestrictedUpdate(*context,
+                           init_events->get_unrestricted_update_events(),
+                           state.get());
+    ApplyUnrestrictedUpdate(init_events->get_unrestricted_update_events(),
+                            state.get(), context);
+  }
+  // Do restricted (discrete variable) updates next.
+  if (init_events->get_discrete_update_events().HasEvents()) {
+    CalcDiscreteVariableUpdate(*context,
+                               init_events->get_discrete_update_events(),
+                               discrete_updates.get());
+    ApplyDiscreteVariableUpdate(init_events->get_discrete_update_events(),
+                                discrete_updates.get(), context);
+  }
+  // Do any publishes last.
+  if (init_events->get_publish_events().HasEvents()) {
+    Publish(*context, init_events->get_publish_events());
+  }
+}
+
 template <typename T>
 std::optional<PeriodicEventData>
     System<T>::GetUniquePeriodicDiscreteUpdateAttribute() const {

systems/framework/system.h

@@ -727,6 +727,16 @@ class System : public SystemBase {
   void GetInitializationEvents(const Context<T>& context,
                                CompositeEventCollection<T>* events) const;
 
+  /** This method triggers all of the initialization events returned by
+  GetInitializationEvents(). The method allocates temporary storage to perform
+  the updates, and is intended only as a convenience method for callers who do
+  not want to use the full Simulator workflow.
+
+  Note that this is not fully equivalent to Simulator::Initialize() because
+  _only_ initialization events are handled here, while Simulator::Initialize()
+  also processes other events associated with time zero. */
+  void ExecuteInitializationEvents(Context<T>* context) const;
+
   /** Determines whether there exists a unique periodic timing (offset and
   period) that triggers one or more discrete update events (and, if so, returns
   that unique periodic timing). Thus, this method can be used (1) as a test to

systems/framework/test/diagram_test.cc

@@ -15,6 +15,7 @@
 #include "drake/systems/framework/fixed_input_port_value.h"
 #include "drake/systems/framework/leaf_system.h"
 #include "drake/systems/framework/output_port.h"
+#include "drake/systems/framework/test_utilities/initialization_test_system.h"
 #include "drake/systems/framework/test_utilities/pack_value.h"
 #include "drake/systems/framework/test_utilities/scalar_conversion.h"
 #include "drake/systems/primitives/adder.h"
@@ -3691,59 +3692,6 @@ GTEST_TEST(RandomContextTest, SetRandomTest) {
 
 // Tests initialization works properly for all subsystems.
 GTEST_TEST(InitializationTest, InitializationTest) {
-  // Note: this class is duplicated in leaf_system_test.
-  class InitializationTestSystem : public LeafSystem<double> {
-   public:
-    InitializationTestSystem() {
-      PublishEvent<double> pub_event(
-          TriggerType::kInitialization,
-          std::bind(&InitializationTestSystem::InitPublish, this,
-                    std::placeholders::_1, std::placeholders::_2));
-      DeclareInitializationEvent(pub_event);
-
-      DeclareInitializationEvent(DiscreteUpdateEvent<double>(
-          TriggerType::kInitialization));
-      DeclareInitializationEvent(UnrestrictedUpdateEvent<double>(
-          TriggerType::kInitialization));
-    }
-
-    bool get_pub_init() const { return pub_init_; }
-    bool get_dis_update_init() const { return dis_update_init_; }
-    bool get_unres_update_init() const { return unres_update_init_; }
-
-   private:
-    void InitPublish(const Context<double>&,
-                     const PublishEvent<double>& event) const {
-      EXPECT_EQ(event.get_trigger_type(),
-                TriggerType::kInitialization);
-      pub_init_ = true;
-    }
-
-    void DoCalcDiscreteVariableUpdates(
-        const Context<double>&,
-        const std::vector<const DiscreteUpdateEvent<double>*>& events,
-        DiscreteValues<double>*) const final {
-      EXPECT_EQ(events.size(), 1);
-      EXPECT_EQ(events.front()->get_trigger_type(),
-                TriggerType::kInitialization);
-      dis_update_init_ = true;
-    }
-
-    void DoCalcUnrestrictedUpdate(
-        const Context<double>&,
-        const std::vector<const UnrestrictedUpdateEvent<double>*>& events,
-        State<double>*) const final {
-      EXPECT_EQ(events.size(), 1);
-      EXPECT_EQ(events.front()->get_trigger_type(),
-                TriggerType::kInitialization);
-      unres_update_init_ = true;
-    }
-
-    mutable bool pub_init_{false};
-    mutable bool dis_update_init_{false};
-    mutable bool unres_update_init_{false};
-  };
-
   DiagramBuilder<double> builder;
 
   auto sys0 = builder.AddSystem<InitializationTestSystem>();
@@ -3752,17 +3700,7 @@ GTEST_TEST(InitializationTest, InitializationTest) {
   auto dut = builder.Build();
 
   auto context = dut->CreateDefaultContext();
-  auto discrete_updates = dut->AllocateDiscreteVariables();
-  auto state = context->CloneState();
-  auto init_events = dut->AllocateCompositeEventCollection();
-  dut->GetInitializationEvents(*context, init_events.get());
-
-  dut->Publish(*context, init_events->get_publish_events());
-  dut->CalcDiscreteVariableUpdate(*context,
-                                  init_events->get_discrete_update_events(),
-                                  discrete_updates.get());
-  dut->CalcUnrestrictedUpdate(
-      *context, init_events->get_unrestricted_update_events(), state.get());
+  dut->ExecuteInitializationEvents(context.get());
 
   EXPECT_TRUE(sys0->get_pub_init());
   EXPECT_TRUE(sys0->get_dis_update_init());