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wpilibj/src/main/java/org/wpilib/smartdashboard/MechanismRoot2d.java

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+// 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.
+
+package edu.wpi.first.wpilibj.smartdashboard;
+
+import edu.wpi.first.networktables.DoublePublisher;
+import edu.wpi.first.networktables.NetworkTable;
+
+/**
+ * Root Mechanism2d node.
+ *
+ * <p>A root is the anchor point of other nodes (such as ligaments).
+ *
+ * <p>Do not create objects of this class directly! Obtain instances from the {@link
+ * Mechanism2d#getRoot(String, double, double)} factory method.
+ *
+ * <p>Append other nodes by using {@link #append(MechanismObject2d)}.
+ */
+public final class MechanismRoot2d extends MechanismObject2d {
+  private double m_x;
+  private DoublePublisher m_xPub;
+  private double m_y;
+  private DoublePublisher m_yPub;
+
+  /**
+   * Package-private constructor for roots.
+   *
+   * @param name name
+   * @param x x coordinate of root (provide only when constructing a root node)
+   * @param y y coordinate of root (provide only when constructing a root node)
+   */
+  MechanismRoot2d(String name, double x, double y) {
+    super(name);
+    m_x = x;
+    m_y = y;
+  }
+
+  @Override
+  public void close() {
+    if (m_xPub != null) {
+      m_xPub.close();
+    }
+    if (m_yPub != null) {
+      m_yPub.close();
+    }
+    super.close();
+  }
+
+  /**
+   * Set the root's position.
+   *
+   * @param x new x coordinate
+   * @param y new y coordinate
+   */
+  public synchronized void setPosition(double x, double y) {
+    m_x = x;
+    m_y = y;
+    flush();
+  }
+
+  @Override
+  protected synchronized void updateEntries(NetworkTable table) {
+    if (m_xPub != null) {
+      m_xPub.close();
+    }
+    m_xPub = table.getDoubleTopic("x").publish();
+    if (m_yPub != null) {
+      m_yPub.close();
+    }
+    m_yPub = table.getDoubleTopic("y").publish();
+    flush();
+  }
+
+  private void flush() {
+    if (m_xPub != null) {
+      m_xPub.set(m_x);
+    }
+    if (m_yPub != null) {
+      m_yPub.set(m_y);
+    }
+  }
+}