java/examples/Topics/Simulate/Springs/applet/Springs.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 Springs extends PApplet {
+
+/**
+ * Springs. 
+ * 
+ * Move the mouse over one of the circles and click to re-position. 
+ * When you release the mouse, it will snap back into position. 
+ * Each circle has a slightly different behavior.  
+ */
+ 
+
+int num = 3; 
+Spring[] springs = new Spring[num]; 
+
+public void setup()
+{
+  size(200, 200);
+  noStroke(); 
+  smooth();
+  springs[0] = new Spring( 70, 160,  20, 0.98f, 8.0f, 0.1f, springs, 0); 
+  springs[1] = new Spring(150, 110,  60, 0.95f, 9.0f, 0.1f, springs, 1); 
+  springs[2] = new Spring( 40,  70, 120, 0.90f, 9.9f, 0.1f, springs, 2);   
+}
+
+public void draw() 
+{
+  background(51); 
+  
+  for (int i = 0; i < num; i++) { 
+    springs[i].update(); 
+    springs[i].display(); 
+  }  
+}
+
+public void mousePressed() 
+{
+  for (int i = 0; i < num; i++) { 
+    springs[i].pressed(); 
+  } 
+}
+
+public void mouseReleased() 
+{
+  for (int i=0; i<num; i++) { 
+    springs[i].released(); 
+  } 
+}
+
+class Spring 
+{ 
+  // Screen values 
+  float xpos, ypos;
+  float tempxpos, tempypos; 
+  int size = 20; 
+  boolean over = false; 
+  boolean move = false; 
+
+  // Spring simulation constants 
+  float mass;       // Mass 
+  float k = 0.2f;    // Spring constant 
+  float damp;       // Damping 
+  float rest_posx;  // Rest position X 
+  float rest_posy;  // Rest position Y 
+
+  // Spring simulation variables 
+  //float pos = 20.0; // Position 
+  float velx = 0.0f;   // X Velocity 
+  float vely = 0.0f;   // Y Velocity 
+  float accel = 0;    // Acceleration 
+  float force = 0;    // Force 
+
+  Spring[] friends;
+  int me;
+  
+  // Constructor
+  Spring(float x, float y, int s, float d, float m, 
+         float k_in, Spring[] others, int id) 
+  { 
+    xpos = tempxpos = x; 
+    ypos = tempypos = y;
+    rest_posx = x;
+    rest_posy = y;
+    size = s;
+    damp = d; 
+    mass = m; 
+    k = k_in;
+    friends = others;
+    me = id; 
+  } 
+
+  public void update() 
+  { 
+    if (move) { 
+      rest_posy = mouseY; 
+      rest_posx = mouseX;
+    } 
+
+    force = -k * (tempypos - rest_posy);  // f=-ky 
+    accel = force / mass;                 // Set the acceleration, f=ma == a=f/m 
+    vely = damp * (vely + accel);         // Set the velocity 
+    tempypos = tempypos + vely;           // Updated position 
+
+    force = -k * (tempxpos - rest_posx);  // f=-ky 
+    accel = force / mass;                 // Set the acceleration, f=ma == a=f/m 
+    velx = damp * (velx + accel);         // Set the velocity 
+    tempxpos = tempxpos + velx;           // Updated position 
+
+    
+    if ((over() || move) && !otherOver() ) { 
+      over = true; 
+    } else { 
+      over = false; 
+    } 
+  } 
+  
+  // Test to see if mouse is over this spring
+  public boolean over() {
+    float disX = tempxpos - mouseX;
+    float disY = tempypos - mouseY;
+    if (sqrt(sq(disX) + sq(disY)) < size/2 ) {
+      return true;
+    } else {
+      return false;
+    }
+  }
+  
+  // Make sure no other springs are active
+  public boolean otherOver() {
+    for (int i=0; i<num; i++) {
+      if (i != me) {
+        if (friends[i].over == true) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  public void display() 
+  { 
+    if (over) { 
+      fill(153); 
+    } else { 
+      fill(255); 
+    } 
+    ellipse(tempxpos, tempypos, size, size);
+  } 
+
+  public void pressed() 
+  { 
+    if (over) { 
+      move = true; 
+    } else { 
+      move = false; 
+    }  
+  } 
+
+  public void released() 
+  { 
+    move = false; 
+    rest_posx = xpos;
+    rest_posy = ypos;
+  } 
+} 
+
+  static public void main(String args[]) {
+    PApplet.main(new String[] { "Springs" });
+  }
+}