refactor rotate

Author: monkstone

contributed/library/branch3D/branch3D.rb

@@ -40,15 +40,15 @@ def run
   def grow
     check_bounds(position + (dir * speed))
     @position += (dir * speed)
-    Rotate.rotate_x!(dir, rand(-0.5..0.5) * THETA)
-    Rotate.rotate_y!(dir, rand(-0.5..0.5) * THETA)
-    Rotate.rotate_z!(dir, rand(-0.5..0.5) * THETA)
+    (0..2).each do |axis|
+      Rotate.axis!(axis, dir, rand(-0.5..0.5) * THETA)
+    end
     path << position
     if (length < MAX_GEN) && (rand < BRANCH_CHANCE)
       branch_dir = dir.copy
-      Rotate.rotate_x!(branch_dir, rand(-0.5..0.5) * BRANCH_THETA)
-      Rotate.rotate_y!(branch_dir, rand(-0.5..0.5) * BRANCH_THETA)
-      Rotate.rotate_z!(branch_dir, rand(-0.5..0.5) * BRANCH_THETA)
+      (0..2).each do |axis|
+        Rotate.axis!(axis, branch_dir, rand(-0.5..0.5) * BRANCH_THETA)
+      end
       self << Branch.new(app, position.copy, branch_dir, speed * 0.99)
     end
     each(&:grow)

contributed/library/branch3D/rotator.rb

@@ -1,31 +1,23 @@
-# Rotator module is required because rotate is not implemented for PiCrate
-# Vec3D (below implementation based on Euler angles)
-# NB: we use quaternions in ArcBall (avoiding possible gimbal lock)
+# Rotator module is required because rotate is not implemented for
+# PiCrate 3D. Here we use Vec2D.rotate! to do Euclid rotation about an
+# axis (we can then apply the rotation to each axis in turn)
+# NB: we use quaternions in ArcBall (to avoid gimbal lock)
 module Rotate
-  def self.rotate_x!(vec, theta)
-    co = Math.cos(theta)
-    si = Math.sin(theta)
-    zz = co * vec.z - si * vec.y
-    vec.y = si * vec.z + co * vec.y
-    vec.z = zz
-    vec
-  end
-
-  def self.rotate_y!(vec, theta)
-    co = Math.cos(theta)
-    si = Math.sin(theta)
-    xx = co * vec.x - si * vec.z
-    vec.z = si * vec.x + co * vec.z
-    vec.x = xx
-    vec
-  end
-
-  def self.rotate_z!(vec, theta)
-    co = Math.cos(theta)
-    si = Math.sin(theta)
-    xx = co * vec.x - si * vec.y
-    vec.y = si * vec.x + co * vec.y
-    vec.x = xx
+  def self.axis!(axis, vec, theta)
+    array = vec.to_a
+    array.slice! axis
+    other = Vec2D.new(*array).rotate! theta
+    case axis
+    when 0 # xaxis
+      vec.y = other.x
+      vec.z = other.y
+    when 1 # yaxis
+      vec.x = other.x
+      vec.z = other.y
+    else # zaxis, by default
+      vec.x = other.x
+      vec.y = other.y
+    end
     vec
   end
 end