Initial Commit

Java/Processing/processing-3.3.6/modes/java/examples/Topics/Interaction/Follow2/Follow2.pde

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+/**
+ * Follow 2  
+ * based on code from Keith Peters. 
+ * 
+ * A two-segmented arm follows the cursor position. The relative
+ * angle between the segments is calculated with atan2() and the
+ * position calculated with sin() and cos().
+ */
+
+float[] x = new float[2];
+float[] y = new float[2];
+float segLength = 50;
+
+void setup() {
+  size(640, 360);
+  strokeWeight(20.0);
+  stroke(255, 100);
+}
+
+void draw() {
+  background(0);
+  dragSegment(0, mouseX, mouseY);
+  dragSegment(1, x[0], y[0]);
+}
+
+void dragSegment(int i, float xin, float yin) {
+  float dx = xin - x[i];
+  float dy = yin - y[i];
+  float angle = atan2(dy, dx);  
+  x[i] = xin - cos(angle) * segLength;
+  y[i] = yin - sin(angle) * segLength;
+  segment(x[i], y[i], angle);
+}
+
+void segment(float x, float y, float a) {
+  pushMatrix();
+  translate(x, y);
+  rotate(a);
+  line(0, 0, segLength, 0);
+  popMatrix();
+}