[glass, wpilib] Rewrite Mechanism2d (#3281)

Substantially improves Mechanism2d by moving it to NetworkTables and adding
a robot API to create the mechanism elements, instead of requiring a JSON file.

Co-authored-by: Peter Johnson <johnson.peter@gmail.com>

wpilibc/src/main/native/include/frc/simulation/Mechanism2D.h

@@ -1,42 +0,0 @@
-// Copyright (c) FIRST and other WPILib contributors.
-// Open Source Software; you can modify and/or share it under the terms of
-// the WPILib BSD license file in the root directory of this project.
-
-#pragma once
-
-#include <map>
-#include <string>
-
-#include <hal/SimDevice.h>
-#include <wpi/StringMap.h>
-
-#include "frc/geometry/Pose2d.h"
-#include "frc/geometry/Rotation2d.h"
-
-namespace frc {
-class Mechanism2D {
- public:
-  Mechanism2D();
-
-  /**
-   * Set/Create the angle of a ligament
-   *
-   * @param ligamentPath json path to the ligament
-   * @param angle to set the ligament
-   */
-  void SetLigamentAngle(const wpi::Twine& ligamentPath, float angle);
-
-  /**
-   * Set/Create the length of a ligament
-   *
-   * @param ligamentPath json path to the ligament
-   * @param length to set the ligament
-   */
-  void SetLigamentLength(const wpi::Twine& ligamentPath, float length);
-
- private:
-  wpi::StringMap<hal::SimDouble> createdItems;
-  hal::SimDevice m_device;
-};
-
-}  // namespace frc

wpilibc/src/main/native/include/frc/smartdashboard/Mechanism2d.h

@@ -0,0 +1,81 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <memory>
+#include <string>
+
+#include <networktables/NetworkTableEntry.h>
+#include <wpi/StringMap.h>
+#include <wpi/mutex.h>
+
+#include "frc/smartdashboard/MechanismRoot2d.h"
+#include "frc/smartdashboard/Sendable.h"
+#include "frc/smartdashboard/SendableHelper.h"
+#include "frc/util/Color8Bit.h"
+
+namespace frc {
+
+/**
+ * Visual 2D representation of arms, elevators, and general mechanisms; through
+ * a node-based API.
+ *
+ * A Mechanism2d object is published and contains at least one root node. Other
+ * nodes (such as ligaments) are recursively based on other nodes.
+ *
+ * Except for the Mechanism2d container object, none of the objects should be
+ * passed or interacted with by value! Obtain pointers from factory methods such
+ * as Mechanism2d.GetRoot() and MechanismObject2d.Append<>(). The Mechanism2d
+ * container object owns the root nodes, and each node internally owns the nodes
+ * based on it. Beware not to let the Mechanism2d object out of scope - all
+ * nodes will be recursively destructed!
+ *
+ * @see MechanismObject2d
+ * @see MechanismLigament2d
+ * @see MechanismRoot2d
+ */
+class Mechanism2d : public Sendable, public SendableHelper<Mechanism2d> {
+ public:
+  /**
+   * Create a new Mechanism2d with the given dimensions and background color.
+   *
+   * @param width the width
+   * @param height the height
+   */
+  Mechanism2d(double width, double height,
+              const Color8Bit& backgroundColor = {0, 0, 32});
+
+  /**
+   * Get or create a root in this Mechanism2d with the given name and
+   * position.
+   *
+   * <p>If a root with the given name already exists, the given x and y
+   * coordinates are not used.
+   *
+   * @param name the root name
+   * @param x the root x coordinate
+   * @param y the root y coordinate
+   * @return a new root object, or the existing one with the given name.
+   */
+  MechanismRoot2d* GetRoot(wpi::StringRef name, double x, double y);
+
+  /**
+   * Set the Mechanism2d background color.
+   *
+   * @param color the new background color
+   */
+  void SetBackgroundColor(const Color8Bit& color);
+
+  void InitSendable(SendableBuilder& builder) override;
+
+ private:
+  double m_width;
+  double m_height;
+  char m_color[10];
+  mutable wpi::mutex m_mutex;
+  std::shared_ptr<nt::NetworkTable> m_table;
+  wpi::StringMap<std::unique_ptr<MechanismRoot2d>> m_roots;
+};
+}  // namespace frc

wpilibc/src/main/native/include/frc/smartdashboard/MechanismLigament2d.h

@@ -0,0 +1,84 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <memory>
+
+#include <networktables/NetworkTableEntry.h>
+#include <units/angle.h>
+
+#include "frc/smartdashboard/MechanismObject2d.h"
+#include "frc/util/Color8Bit.h"
+
+namespace frc {
+
+/**
+ * Ligament node on a Mechanism2d.
+ *
+ * @see Mechanism2d
+ */
+class MechanismLigament2d : public MechanismObject2d {
+ public:
+  MechanismLigament2d(const wpi::Twine& name, double length,
+                      units::degree_t angle, double lineWidth = 6,
+                      const frc::Color8Bit& color = {235, 137, 52});
+
+  /**
+   * Set the ligament color.
+   *
+   * @param color the color of the line
+   */
+  void SetColor(const frc::Color8Bit& color);
+
+  /**
+   * Set the ligament's length.
+   *
+   * @param length the line length
+   */
+  void SetLength(double length);
+
+  /**
+   * Get the ligament length.
+   *
+   * @return the line length
+   */
+  double GetLength();
+
+  /**
+   * Set the ligament's angle relative to its parent.
+   *
+   * @param degrees the angle
+   */
+  void SetAngle(units::degree_t angle);
+
+  /**
+   * Get the ligament's angle relative to its parent.
+   *
+   * @return the angle
+   */
+  double GetAngle();
+
+  /**
+   * Set the line thickness.
+   *
+   * @param weight the line thickness
+   */
+  void SetLineWeight(double lineWidth);
+
+ protected:
+  void UpdateEntries(std::shared_ptr<NetworkTable> table) override;
+
+ private:
+  void Flush();
+  double m_length;
+  nt::NetworkTableEntry m_lengthEntry;
+  double m_angle;
+  nt::NetworkTableEntry m_angleEntry;
+  double m_weight;
+  nt::NetworkTableEntry m_weightEntry;
+  char m_color[10];
+  nt::NetworkTableEntry m_colorEntry;
+};
+}  // namespace frc

wpilibc/src/main/native/include/frc/smartdashboard/MechanismObject2d.h

@@ -0,0 +1,88 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include <networktables/NetworkTable.h>
+#include <wpi/StringMap.h>
+#include <wpi/Twine.h>
+
+namespace frc {
+
+/**
+ * Common base class for all Mechanism2d node types.
+ *
+ * To append another node, call Append with the type of node and its
+ * construction parameters. None of the node types are designed to be
+ * constructed directly, and are owned by their parent node/container - obtain
+ * pointers from the Append function or similar factory methods.
+ *
+ * @see Mechanism2d.
+ */
+class MechanismObject2d {
+  friend class Mechanism2d;
+
+ protected:
+  explicit MechanismObject2d(const wpi::Twine& name);
+
+  /**
+   * Update all entries with new ones from a new table.
+   *
+   * @param table the new table.
+   */
+  virtual void UpdateEntries(std::shared_ptr<NetworkTable> table) = 0;
+
+  mutable wpi::mutex m_mutex;
+
+ public:
+  virtual ~MechanismObject2d() = default;
+
+  /**
+   * Retrieve the object's name.
+   *
+   * @return the object's name relative to its parent.
+   */
+  const std::string& GetName() const;
+
+  /**
+   * Append a Mechanism object that is based on this one.
+   *
+   * @param name the name of the new object.
+   * @param args constructor arguments of the object type.
+   * @return the constructed and appended object, useful for variable
+   * assignments and call chaining.
+   * @throw if an object with the given name already exists.
+   */
+  template <typename T, typename... Args,
+            typename =
+                std::enable_if_t<std::is_convertible_v<T*, MechanismObject2d*>>>
+  T* Append(wpi::StringRef name, Args&&... args) {
+    std::scoped_lock lock(m_mutex);
+    auto& obj = m_objects[name];
+    if (obj) {
+      throw std::runtime_error(("MechanismObject names must be unique! `" +
+                                name + "` was inserted twice!")
+                                   .str());
+    }
+    obj = std::make_unique<T>(name, std::forward<Args>(args)...);
+    T* ex = static_cast<T*>(obj.get());
+    if (m_table) {
+      ex->Update(m_table->GetSubTable(name));
+    }
+    return ex;
+  }
+
+ private:
+  std::string m_name;
+  wpi::StringMap<std::unique_ptr<MechanismObject2d>> m_objects;
+  std::shared_ptr<NetworkTable> m_table;
+  void Update(std::shared_ptr<NetworkTable> table);
+};
+}  // namespace frc

wpilibc/src/main/native/include/frc/smartdashboard/MechanismRoot2d.h

@@ -0,0 +1,49 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <memory>
+
+#include <networktables/NetworkTableEntry.h>
+#include <wpi/Twine.h>
+
+#include "MechanismObject2d.h"
+
+namespace frc {
+
+/**
+ * Root Mechanism2d node.
+ *
+ * Do not create objects of this class directly! Obtain pointers from the
+ * Mechanism2d.GetRoot() factory method.
+ */
+class MechanismRoot2d : private MechanismObject2d {
+  friend class Mechanism2d;
+  struct private_init {};
+
+ public:
+  MechanismRoot2d(const wpi::Twine& name, double x, double y,
+                  const private_init&);
+
+  /**
+   * Set the root's position.
+   *
+   * @param x new x coordinate
+   * @param y new y coordinate
+   */
+  void SetPosition(double x, double y);
+
+  using MechanismObject2d::GetName;
+
+  using MechanismObject2d::Append;
+
+ private:
+  void UpdateEntries(std::shared_ptr<NetworkTable> table) override;
+  inline void Flush();
+  double m_x;
+  double m_y;
+  nt::NetworkTableEntry m_posEntry;
+};
+}  // namespace frc