java/examples/Topics/Interaction/Reach3/applet/Reach3.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 Reach3 extends PApplet {
+
+/**
+ * Reach 3. 
+ * Based on code from Keith Peters (www.bit-101.com)
+ * 
+ * The arm follows the position of the ball by
+ * calculating the angles with atan2().
+ */
+
+int numSegments = 6;
+float[] x = new float[numSegments];
+float[] y = new float[numSegments];
+float[] angle = new float[numSegments];
+float segLength = 15;
+float targetX, targetY;
+
+float ballX = 50;
+float ballY = 50;
+int ballXDirection = 1;
+int ballYDirection = -1;
+
+public void setup() {
+  size(200, 200);
+  smooth(); 
+  strokeWeight(20.0f);
+  stroke(0, 100);
+  noFill();
+  x[x.length-1] = width/2;     // Set base x-coordinate
+  y[x.length-1] = height;  // Set base y-coordinate
+}
+
+public void draw() {
+  background(226);
+  
+  strokeWeight(20);
+  ballX = ballX + 1.0f * ballXDirection;
+  ballY = ballY + 0.8f * ballYDirection;
+  if(ballX > width-25 || ballX < 25) {
+    ballXDirection *= -1; 
+  }
+  if(ballY > height-25 || ballY < 25) {
+    ballYDirection *= -1; 
+  }
+  ellipse(ballX, ballY, 30, 30);
+  
+  reachSegment(0, ballX, ballY);
+  for(int i=1; i<numSegments; i++) {
+    reachSegment(i, targetX, targetY);
+  }
+  for(int i=x.length-1; i>=1; i--) {
+    positionSegment(i, i-1);  
+  } 
+  for(int i=0; i<x.length; i++) {
+    segment(x[i], y[i], angle[i], (i+1)*2); 
+  }
+}
+
+public void positionSegment(int a, int b) {
+  x[b] = x[a] + cos(angle[a]) * segLength;
+  y[b] = y[a] + sin(angle[a]) * segLength; 
+}
+
+public void reachSegment(int i, float xin, float yin) {
+  float dx = xin - x[i];
+  float dy = yin - y[i];
+  angle[i] = atan2(dy, dx);  
+  targetX = xin - cos(angle[i]) * segLength;
+  targetY = yin - sin(angle[i]) * segLength;
+}
+
+public void segment(float x, float y, float a, float sw) {
+  strokeWeight(sw);
+  pushMatrix();
+  translate(x, y);
+  rotate(a);
+  line(0, 0, segLength, 0);
+  popMatrix();
+}
+
+  static public void main(String args[]) {
+    PApplet.main(new String[] { "Reach3" });
+  }
+}

java/examples/Topics/Interaction/Reach3/applet/Reach3.pde

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+/**
+ * Reach 3. 
+ * Based on code from Keith Peters (www.bit-101.com)
+ * 
+ * The arm follows the position of the ball by
+ * calculating the angles with atan2().
+ */
+
+int numSegments = 6;
+float[] x = new float[numSegments];
+float[] y = new float[numSegments];
+float[] angle = new float[numSegments];
+float segLength = 15;
+float targetX, targetY;
+
+float ballX = 50;
+float ballY = 50;
+int ballXDirection = 1;
+int ballYDirection = -1;
+
+void setup() {
+  size(200, 200);
+  smooth(); 
+  strokeWeight(20.0);
+  stroke(0, 100);
+  noFill();
+  x[x.length-1] = width/2;     // Set base x-coordinate
+  y[x.length-1] = height;  // Set base y-coordinate
+}
+
+void draw() {
+  background(226);
+  
+  strokeWeight(20);
+  ballX = ballX + 1.0 * ballXDirection;
+  ballY = ballY + 0.8 * ballYDirection;
+  if(ballX > width-25 || ballX < 25) {
+    ballXDirection *= -1; 
+  }
+  if(ballY > height-25 || ballY < 25) {
+    ballYDirection *= -1; 
+  }
+  ellipse(ballX, ballY, 30, 30);
+  
+  reachSegment(0, ballX, ballY);
+  for(int i=1; i<numSegments; i++) {
+    reachSegment(i, targetX, targetY);
+  }
+  for(int i=x.length-1; i>=1; i--) {
+    positionSegment(i, i-1);  
+  } 
+  for(int i=0; i<x.length; i++) {
+    segment(x[i], y[i], angle[i], (i+1)*2); 
+  }
+}
+
+void positionSegment(int a, int b) {
+  x[b] = x[a] + cos(angle[a]) * segLength;
+  y[b] = y[a] + sin(angle[a]) * segLength; 
+}
+
+void reachSegment(int i, float xin, float yin) {
+  float dx = xin - x[i];
+  float dy = yin - y[i];
+  angle[i] = atan2(dy, dx);  
+  targetX = xin - cos(angle[i]) * segLength;
+  targetY = yin - sin(angle[i]) * segLength;
+}
+
+void segment(float x, float y, float a, float sw) {
+  strokeWeight(sw);
+  pushMatrix();
+  translate(x, y);
+  rotate(a);
+  line(0, 0, segLength, 0);
+  popMatrix();
+}