Better motion with Perlin noise

Author: jeffThompson

InteractionAndGames/Wind/Wind.pde

@@ -3,27 +3,36 @@
 WIND
 Jeff Thompson | 2015 | www.jeffreythompson.org
 
-A simple simulation of wind blowing a tree. This is essentially
-Brownian Motion applied to an angle – the angle of the tree (which
-is bent by the wind) moves back-and-forth randomly, just like
-an ant wandering around.
+A simple simulation of wind blowing a tree. The angle of the 
+tree (which is bent by the "wind") moves back-and-forth randomly
+using Perlin noise, a more realistic way to get random motion.
 
-A fancier version, commented out, using a recursive function to
-draw a Pythagoras Tree.
+Invented in the 1980s by Ken Perlin, it has been used in movies
+and games for 35+ years to generate clouds, terrain, and other
+organic features.
+
+Our "tree" is really just a line and a circle: a fancier version, 
+commented out, using a recursive function to draw a Pythagoras 
+Tree instead of a line-and-circle.
 
 CHALLENGES:
 +  How might you visualize the wind onscreen?
 +  Can you draw grass or other elements that are effected by the
    same global wind?
++  Can you draw a leaf at the end of each branch? What about just
+   the branches where recursion reaches the minimum length?
 
 */
 
-float trunkLen =    150;    // length of the trunk
-float angle =       0;      // starting wind angle
+float trunkLen =    150;        // length of the trunk
+float windInc =     0.01;       // how quickly the wind changes speed (try changing)
 
 // for Pythagoras Tree version
-float branchAngle = 30;     // angle between branches
-int minSize =       10;     // minimum size of branches
+float branchAngle = 30;         // angle between two branches
+int minSize =       10;         // minimum size of branches
+
+float windSpeed =   0;          // speed, which will = angle of bend
+float noisePos =    0;          // "position" in the Perlin noise
 
 
 void setup() {
@@ -39,7 +48,7 @@ void draw() {
   // draw a simple tree
   pushMatrix();
   translate(width/2, height);
-  rotate(radians(angle));
+  rotate(radians(windSpeed));
   stroke(10);
   line(0,0, 0,-trunkLen);
   fill(255, 100);
@@ -51,28 +60,34 @@ void draw() {
   // of fractal pattern using a recursive function
   /*
   translate(width/2, height);
-  rotate(radians(angle));
+  rotate(radians(windSpeed));
   stroke(255);
   line(0,0, 0,-trunkLen);
   branch(trunkLen);
   */
 
-  // update angle with random wind speed
-  angle += random(-0.5,0.5);
-  if (angle > 45) angle = 45;      // don't go too far
-  else if (angle < 0) angle = 0;
+  // update wind speed using 1D Perlin noise
+  // noise() returns a value 0 to 1, so mult by 45 means
+  // the wind speed will be 0-45º
+  windSpeed = noise(noisePos) * 45;
+  noisePos += windInc;
+  
+  // random() will generate movement that is jerky and unrealistic
+  // try this instead and see what happens
+  // windSpeed += random(-0.6,0.5);
 }
 
 
 // a "recursive" function to draw the tree
+// for more information on recursive functions, see Basics > Recursion
 void branch (float s) {
 
   // store previous and reduce branch length
   float prevS = s;
   s *= 0.5 * sqrt(2);    // experiment with changing and see what happens
 
   // add some twist based on the wind speed
-  float twist = map(angle, 0,45, 0,30);
+  float twist = map(windSpeed, 0,45, 0,30);
 
   // keep going until the branches are too small
   if (s > minSize) {