java/examples/Topics/Simulate/Spring/applet/Spring.java

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+import processing.core.*; 
+
+import java.applet.*; 
+import java.awt.*; 
+import java.awt.image.*; 
+import java.awt.event.*; 
+import java.io.*; 
+import java.net.*; 
+import java.text.*; 
+import java.util.*; 
+import java.util.zip.*; 
+import java.util.regex.*; 
+
+public class Spring extends PApplet {
+
+/**
+ * Spring. 
+ * 
+ * Click, drag, and release the horizontal bar to start the spring. 
+ */
+ 
+// Spring drawing constants for top bar
+int s_height = 16;     // Height
+int left = 50;         // Left position
+int right = 150;       // Right position
+int max = 100;         // Maximum Y value
+int min = 20;          // Minimum Y value
+boolean over = false;  // If mouse over
+boolean move = false;  // If mouse down and over
+
+// Spring simulation constants
+float M = 0.8f;   // Mass
+float K = 0.2f;   // Spring constant
+float D = 0.92f;  // Damping
+float R = 60;    // Rest position
+
+// Spring simulation variables
+float ps = 60.0f; // Position
+float vs = 0.0f;  // Velocity
+float as = 0;    // Acceleration
+float f = 0;     // Force
+
+
+public void setup() 
+{
+  size(200, 200);
+  rectMode(CORNERS);
+  noStroke();
+}
+
+public void draw() 
+{
+  background(102);
+  updateSpring();
+  drawSpring();
+}
+
+public void drawSpring() 
+{
+  // Draw base
+  fill(0.2f);
+  float b_width = 0.5f * ps + -8;
+  rect(width/2 - b_width, ps + s_height, width/2 + b_width, 150);
+
+  // Set color and draw top bar
+  if(over || move) { 
+    fill(255);
+  } else { 
+    fill(204);
+  }
+  rect(left, ps, right, ps + s_height);
+}
+
+
+public void updateSpring()
+{
+  // Update the spring position
+  if(!move) {
+    f = -K * (ps - R);    // f=-ky
+    as = f / M;           // Set the acceleration, f=ma == a=f/m
+    vs = D * (vs + as);   // Set the velocity
+    ps = ps + vs;         // Updated position
+  }
+  if(abs(vs) < 0.1f) {
+    vs = 0.0f;
+  }
+
+  // Test if mouse is over the top bar
+  if(mouseX > left && mouseX < right && mouseY > ps && mouseY < ps + s_height) {
+    over = true;
+  } else {
+    over = false;
+  }
+  
+  // Set and constrain the position of top bar
+  if(move) {
+    ps = mouseY - s_height/2;
+    if (ps < min) { ps = min; } 
+    if (ps > max) { ps = max; }
+  }
+}
+
+public void mousePressed() {
+  if(over) {
+    move = true;
+  }
+}
+
+public void mouseReleased()
+{
+  move = false;
+}
+
+  static public void main(String args[]) {
+    PApplet.main(new String[] { "Spring" });
+  }
+}