WIP hand matrix

lib/bone.js

@@ -62,7 +62,8 @@ var Bone = module.exports = function(finger, data) {
   /**
    *
    * These fully-specify the orientation of the bone.
-   * See examples/threejs-bones.html for more info
+   * See examples/threejs-bones.html or https://developer.leapmotion.com/gallery/bone-basis-arrows for more info
+   *
    * Three vec3s:
    *  x (red): The rotation axis of the finger, pointing outwards.  (In general, away from the thumb )
    *  y (green): The "up" vector, orienting the top of the finger
@@ -74,6 +75,7 @@ var Bone = module.exports = function(finger, data) {
    *  the first two appear in the same position, but only the second (proximal) rotates.
    *
    *  Normalized.
+   *
    */
   this.basis = data.basis;
 };

lib/hand.js

@@ -193,7 +193,8 @@ var Hand = module.exports = function(data) {
    this.grabStrength = data.grabStrength;
    this.pinchStrength = data.pinchStrength;
    this.confidence = data.confidence;
-}
+   this._matrix = null;
+};
 
 /**
  * The finger with the specified ID attached to this hand.
@@ -422,6 +423,31 @@ Hand.prototype.roll = function() {
   return Math.atan2(this.palmNormal[0], -this.palmNormal[1]);
 }
 
+// Returns the 4x4 transformation Matrix for this hand, which contains rotation, position, and scale data.
+// Good for compatability with THREE.js Matrix4#fromArray()
+Hand.prototype.matrix = function(){
+
+  if (this._matrix) return this._matrix;
+
+  var cross = vec3.create();
+  vec3.cross(cross, this.palmNormal, this.direction);
+
+  var up = vec3.clone(this.palmNormal);
+  vec3.scale(up, up, -1);
+
+  var b = this.basis,
+      t = this._matrix = mat4.create();
+
+
+  // open transform mat4 from rotation mat3
+  t[0] = cross[0], t[1] = cross[1], t[2]  = cross[2];
+  t[4] = up[0], t[5] = up[1], t[6]  = up[2];
+  t[8] = this.direction[0], t[9] = this.direction[1], t[10] = this.direction[2];
+
+
+
+}
+
 /**
  * An invalid Hand object.
  *

test/hand.js

@@ -51,6 +51,40 @@ describe('Hand', function(){
         assert.closeTo(0.72273, result, 0.0001)
       })
     })
+
+    it('should have a transform matrix', function() {
+
+      var matrix = hand.matrix();
+
+      //scale
+      assert(matrix[3] == 1);
+      assert(matrix[7] == 1);
+      assert(matrix[11] == 1);
+      assert(matrix[15] == 1);
+
+      //position
+      assert(matrix[12] = hand.palmPosition[0]);
+      assert(matrix[13] = hand.palmPosition[1]);
+      assert(matrix[14] = hand.palmPosition[2]);
+
+      // rotation
+      assert(matrix[4] = -hand.palmNormal[0]);
+      assert(matrix[5] = -hand.palmNormal[1]);
+      assert(matrix[6] = -hand.palmNormal[2]);
+
+      assert(matrix[8] =  hand.direction[0]);
+      assert(matrix[9] =  hand.direction[1]);
+      assert(matrix[10] = hand.direction[2]);
+
+      var cross = vec3.create();
+      vec3.cross(cross, this.palmNormal, this.direction);
+
+      assert(matrix[0] =  hand.direction[0]);
+      assert(matrix[1] =  hand.direction[1]);
+      assert(matrix[2] = hand.direction[2]);
+
+
+    })
   });
 
   describe('#translation()', function(){