Re-adding Topics to SVN

java/examples/Topics/Simulate/SimpleParticleSystem/Particle.pde

@@ -0,0 +1,67 @@
+// A simple Particle class
+
+class Particle {
+  PVector loc;
+  PVector vel;
+  PVector acc;
+  float r;
+  float timer;
+  
+  // Another constructor (the one we are using here)
+  Particle(PVector l) {
+    acc = new PVector(0,0.05,0);
+    vel = new PVector(random(-1,1),random(-2,0),0);
+    loc = l.get();
+    r = 10.0;
+    timer = 100.0;
+  }
+
+  void run() {
+    update();
+    render();
+  }
+
+  // Method to update location
+  void update() {
+    vel.add(acc);
+    loc.add(vel);
+    timer -= 1.0;
+  }
+
+  // Method to display
+  void render() {
+    ellipseMode(CENTER);
+    stroke(255,timer);
+    fill(100,timer);
+    ellipse(loc.x,loc.y,r,r);
+    displayVector(vel,loc.x,loc.y,10);
+  }
+  
+  // Is the particle still useful?
+  boolean dead() {
+    if (timer <= 0.0) {
+      return true;
+    } else {
+      return false;
+    }
+  }
+  
+   void displayVector(PVector v, float x, float y, float scayl) {
+    pushMatrix();
+    float arrowsize = 4;
+    // Translate to location to render vector
+    translate(x,y);
+    stroke(255);
+    // Call vector heading function to get direction (note that pointing up is a heading of 0) and rotate
+    rotate(v.heading2D());
+    // Calculate length of vector & scale it to be bigger or smaller if necessary
+    float len = v.mag()*scayl;
+    // Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)
+    line(0,0,len,0);
+    line(len,0,len-arrowsize,+arrowsize/2);
+    line(len,0,len-arrowsize,-arrowsize/2);
+    popMatrix();
+  } 
+
+}
+