Re-adding Topics to SVN

java/examples/Topics/Interaction/Follow1/Follow1.pde

@@ -0,0 +1,39 @@
+/**
+ * Follow 1. 
+ * Based on code from Keith Peters (www.bit-101.com). 
+ * 
+ * A line segment is pushed and pulled by the cursor.
+ */
+
+float x = 100;
+float y = 100;
+float angle1 = 0.0;
+float segLength = 50;
+
+void setup() {
+  size(200, 200);
+  smooth(); 
+  strokeWeight(20.0);
+  stroke(0, 100);
+}
+
+void draw() {
+  background(226);
+  
+  float dx = mouseX - x;
+  float dy = mouseY - y;
+  angle1 = atan2(dy, dx);  
+  x = mouseX - (cos(angle1) * segLength);
+  y = mouseY - (sin(angle1) * segLength);
+ 
+  segment(x, y, angle1); 
+  ellipse(x, y, 20, 20);
+}
+
+void segment(float x, float y, float a) {
+  pushMatrix();
+  translate(x, y);
+  rotate(a);
+  line(0, 0, segLength, 0);
+  popMatrix();
+}