Data commit

Task/Animate-a-pendulum/Scala/animate-a-pendulum.scala

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+import java.awt.Color
+import java.util.concurrent.{Executors, TimeUnit}
+
+import scala.swing.{Graphics2D, MainFrame, Panel, SimpleSwingApplication}
+import scala.swing.Swing.pair2Dimension
+
+object Pendulum extends SimpleSwingApplication {
+  val length = 100
+
+  lazy val ui = new Panel {
+    import scala.math.{cos, Pi, sin}
+
+    background = Color.white
+    preferredSize = (2 * length + 50, length / 2 * 3)
+    peer.setDoubleBuffered(true)
+
+    var angle: Double = Pi / 2
+
+    override def paintComponent(g: Graphics2D): Unit = {
+      super.paintComponent(g)
+
+      val (anchorX, anchorY) = (size.width / 2, size.height / 4)
+      val (ballX, ballY) =
+        (anchorX + (sin(angle) * length).toInt, anchorY + (cos(angle) * length).toInt)
+      g.setColor(Color.lightGray)
+      g.drawLine(anchorX - 2 * length, anchorY, anchorX + 2 * length, anchorY)
+      g.setColor(Color.black)
+      g.drawLine(anchorX, anchorY, ballX, ballY)
+      g.fillOval(anchorX - 3, anchorY - 4, 7, 7)
+      g.drawOval(ballX - 7, ballY - 7, 14, 14)
+      g.setColor(Color.yellow)
+      g.fillOval(ballX - 7, ballY - 7, 14, 14)
+    }
+
+    val animate: Runnable = new Runnable {
+      var angleVelocity = 0.0
+      var dt = 0.1
+
+      override def run(): Unit = {
+        angleVelocity += -9.81 / length * Math.sin(angle) * dt
+        angle += angleVelocity * dt
+        repaint()
+      }
+    }
+  }
+
+  override def top = new MainFrame {
+    title = "Rosetta Code >>> Task: Animate a pendulum | Language: Scala"
+    contents = ui
+    centerOnScreen()
+    Executors.
+      newSingleThreadScheduledExecutor().
+      scheduleAtFixedRate(ui.animate, 0, 15, TimeUnit.MILLISECONDS)
+  }
+}