view org/body.org @ 217:7bf3e3d8fb26

added source repository links
author Robert McIntyre <rlm@mit.edu>
date Fri, 10 Feb 2012 11:37:19 -0700
parents f283c62bd212
children 63dafe7365df
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1 #+title: Building a Body
2 #+author: Robert McIntyre
3 #+email: rlm@mit.edu
4 #+description: Simulating a body (movement, touch, propioception) in jMonkeyEngine3.
5 #+SETUPFILE: ../../aurellem/org/setup.org
6 #+INCLUDE: ../../aurellem/org/level-0.org
8 * Design Constraints
10 I use [[www.blender.org/][blender]] to design bodies. The design of the bodies is
11 determined by the requirements of the AI that will use them. The
12 bodies must be easy for an AI to sense and control, and they must be
13 relatively simple for jMonkeyEngine to compute.
15 ** Bag of Bones
17 How to create such a body? One option I ultimately rejected is to use
18 blender's [[http://wiki.blender.org/index.php/Doc:2.6/Manual/Rigging/Armatures][armature]] system. The idea would have been to define a mesh
19 which describes the creature's entire body. To this you add an
20 (skeleton) which deforms this mesh. This technique is used extensively
21 to model humans and create realistic animations. It is hard to use for
22 my purposes because it is difficult to update the creature's Physics
23 Collision Mesh in tandem with its Geometric Mesh under the influence
24 of the armature. Withouth this the creature will not be able to grab
25 things in its environment, and it won't be able to tell where its
26 physical body is by using its eyes. Also, armatures do not specify
27 any rotational limits for a joint, making it hard to model elbows,
28 shoulders, etc.
30 ** EVE
32 Instead of using the human-like "deformable bag of bones" approach, I
33 decided to base my body plans on the robot EVE from the movie wall-E.
35 #+caption: EVE from the movie WALL-E. This body plan turns out to be much better suited to my purposes than a more human-like one.
36 [[../images/Eve.jpg]]
38 EVE's body is composed of several rigid components that are held
39 together by invisible joint constraints. This is what I mean by
40 "eve-like". The main reason that I use eve-style bodies is so that
41 there will be correspondence between the AI's vision and the physical
42 presence of its body. Each individual section is simulated by a
43 separate rigid body that corresponds exactly with its visual
44 representation and does not change. Sections are connected by
45 invisible joints that are well supported in jMonkyeEngine. Bullet, the
46 physics backend for jMonkeyEngine, can efficiently simulate hundreds
47 of rigid bodies connected by joints. Sections do not have to stay as
48 one piece forever; they can be dynamically replaced with multiple
49 sections to simulate splitting in two. This could be used to simulate
50 retractable claws or EVE's hands, which are able to coalece into one
51 object in the movie.
53 * Solidifying the Body
55 Here is a hand designed eve-style in blender.
57 #+attr_html: width="755"
58 [[../images/hand-screenshot0.png]]
60 If we load it directly into jMonkeyEngine, we get this:
62 #+name: test-1
63 #+begin_src clojure
64 (def hand-path "Models/test-creature/hand.blend")
66 (defn hand [] (load-blender-model hand-path))
68 (defn setup [world]
69 (let [cam (.getCamera world)]
70 (println-repl cam)
71 (.setLocation
72 cam (Vector3f.
73 -6.9015837, 8.644911, 5.6043186))
74 (.setRotation
75 cam
76 (Quaternion.
77 0.14046453, 0.85894054, -0.34301838, 0.3533118)))
78 (light-up-everything world)
79 (.setTimer world (RatchetTimer. 60))
80 world)
82 (defn test-one []
83 (world (hand)
84 standard-debug-controls
85 (comp
86 #(Capture/captureVideo
87 % (File. "/home/r/proj/cortex/render/body/1"))
88 setup)
89 no-op))
90 #+end_src
93 #+begin_src clojure :results silent
94 (.start (cortex.test.body/test-one))
95 #+end_src
97 #+begin_html
98 <div class="figure">
99 <center>
100 <video controls="controls" width="640">
101 <source src="../video/ghost-hand.ogg" type="video/ogg"
102 preload="none" poster="../images/aurellem-1280x480.png" />
103 </video>
104 </center>
105 <p>The hand model directly loaded from blender. It has no physical
106 presense in the simulation. </p>
107 </div>
108 #+end_html
110 You will notice that the hand has no physical presence -- it's a
111 hologram through which everything passes. Therefore, the first thing
112 to do is to make it solid. Blender has physics simulation on par with
113 jMonkeyEngine (they both use bullet as their physics backend), but it
114 can be difficult to translate between the two systems, so for now I
115 specify the mass of each object as meta-data in blender and construct
116 the physics shape based on the mesh in jMonkeyEngine.
118 #+name: body-1
119 #+begin_src clojure
120 (defn physical!
121 "Iterate through the nodes in creature and make them real physical
122 objects in the simulation."
123 [#^Node creature]
124 (dorun
125 (map
126 (fn [geom]
127 (let [physics-control
128 (RigidBodyControl.
129 (HullCollisionShape.
130 (.getMesh geom))
131 (if-let [mass (meta-data geom "mass")]
132 (do
133 (println-repl
134 "setting" (.getName geom) "mass to" (float mass))
135 (float mass))
136 (float 1)))]
137 (.addControl geom physics-control)))
138 (filter #(isa? (class %) Geometry )
139 (node-seq creature)))))
140 #+end_src
142 =(physical!)= iterates through a creature's node structure, creating
143 CollisionShapes for each geometry with the mass specified in that
144 geometry's meta-data.
146 #+name: test-2
147 #+begin_src clojure
148 (in-ns 'cortex.test.body)
150 (def gravity-control
151 {"key-g" (fn [world _]
152 (set-gravity world (Vector3f. 0 -9.81 0)))
153 "key-u" (fn [world _] (set-gravity world Vector3f/ZERO))})
156 (defn floor []
157 (box 10 3 10 :position (Vector3f. 0 -10 0)
158 :color ColorRGBA/Gray :mass 0))
160 (defn test-two []
161 (world (nodify
162 [(doto (hand)
163 (physical!))
164 (floor)])
165 (merge standard-debug-controls gravity-control)
166 (comp
167 #(Capture/captureVideo
168 % (File. "/home/r/proj/cortex/render/body/2"))
169 #(do (set-gravity % Vector3f/ZERO) %)
170 setup)
171 no-op))
172 #+end_src
174 #+begin_html
175 <div class="figure">
176 <center>
177 <video controls="controls" width="640">
178 <source src="../video/crumbly-hand.ogg" type="video/ogg"
179 preload="none" poster="../images/aurellem-1280x480.png" />
180 </video>
181 </center>
182 <p>The hand now has a physical presence, but there is nothing to hold
183 it together.</p>
184 </div>
185 #+end_html
187 Now that's some progress.
189 * Joints
191 Obviously, an AI is not going to be doing much while lying in pieces
192 on the floor. So, the next step to making a proper body is to connect
193 those pieces together with joints. jMonkeyEngine has a large array of
194 joints available via bullet, such as Point2Point, Cone, Hinge, and a
195 generic Six Degree of Freedom joint, with or without spring
196 restitution.
198 Although it should be possible to specify the joints using blender's
199 physics system, and then automatically import them with jMonkeyEngine,
200 the support isn't there yet, and there are a few problems with bullet
201 itself that need to be solved before it can happen.
203 So, I will use the same system for specifying joints as I will do for
204 some senses. Each joint is specified by an empty node whose parent
205 has the name "joints". Their orientation and meta-data determine what
206 joint is created.
208 #+attr_html: width="755"
209 #+caption: Joints hack in blender. Each empty node here will be transformed into a joint in jMonkeyEngine
210 [[../images/hand-screenshot1.png]]
212 The empty node in the upper right, highlighted in yellow, is the
213 parent node of all the emptys which represent joints. The following
214 functions must do three things to translate these into real joints:
216 - Find the children of the "joints" node.
217 - Determine the two spatials the joint it meant to connect.
218 - Create the joint based on the meta-data of the empty node.
220 ** Finding the Joints
222 The higher order function =(sense-nodes)= from =cortex.sense= simplifies
223 the first task.
225 #+name: joints-2
226 #+begin_src clojure
227 (defvar
228 ^{:arglists '([creature])}
229 joints
230 (sense-nodes "joints")
231 "Return the children of the creature's \"joints\" node.")
232 #+end_src
235 ** Joint Targets and Orientation
237 This technique for finding a joint's targets is very similiar to
238 =(cortex.sense/closest-node)=. A small cube, centered around the
239 empty-node, grows exponentially until it intersects two /physical/
240 objects. The objects are ordered according to the joint's rotation,
241 with the first one being the object that has more negative coordinates
242 in the joint's reference frame. Since the objects must be physical,
243 the empty-node itself escapes detection. Because the objects must be
244 physical, =(joint-targets)= must be called /after/ =(physical!)= is
245 called.
247 #+name: joints-3
248 #+begin_src clojure
249 (defn joint-targets
250 "Return the two closest two objects to the joint object, ordered
251 from bottom to top according to the joint's rotation."
252 [#^Node parts #^Node joint]
253 (loop [radius (float 0.01)]
254 (let [results (CollisionResults.)]
255 (.collideWith
256 parts
257 (BoundingBox. (.getWorldTranslation joint)
258 radius radius radius) results)
259 (let [targets
260 (distinct
261 (map #(.getGeometry %) results))]
262 (if (>= (count targets) 2)
263 (sort-by
264 #(let [joint-ref-frame-position
265 (jme-to-blender
266 (.mult
267 (.inverse (.getWorldRotation joint))
268 (.subtract (.getWorldTranslation %)
269 (.getWorldTranslation joint))))]
270 (.dot (Vector3f. 1 1 1) joint-ref-frame-position))
271 (take 2 targets))
272 (recur (float (* radius 2))))))))
273 #+end_src
275 ** Generating Joints
277 This section of code iterates through all the different ways of
278 specifying joints using blender meta-data and converts each one to the
279 appropriate jMonkyeEngine joint.
281 #+name: joints-4
282 #+begin_src clojure
283 (defmulti joint-dispatch
284 "Translate blender pseudo-joints into real JME joints."
285 (fn [constraints & _]
286 (:type constraints)))
288 (defmethod joint-dispatch :point
289 [constraints control-a control-b pivot-a pivot-b rotation]
290 (println-repl "creating POINT2POINT joint")
291 ;; bullet's point2point joints are BROKEN, so we must use the
292 ;; generic 6DOF joint instead of an actual Point2Point joint!
294 ;; should be able to do this:
295 (comment
296 (Point2PointJoint.
297 control-a
298 control-b
299 pivot-a
300 pivot-b))
302 ;; but instead we must do this:
303 (println-repl "substuting 6DOF joint for POINT2POINT joint!")
304 (doto
305 (SixDofJoint.
306 control-a
307 control-b
308 pivot-a
309 pivot-b
310 false)
311 (.setLinearLowerLimit Vector3f/ZERO)
312 (.setLinearUpperLimit Vector3f/ZERO)))
314 (defmethod joint-dispatch :hinge
315 [constraints control-a control-b pivot-a pivot-b rotation]
316 (println-repl "creating HINGE joint")
317 (let [axis
318 (if-let
319 [axis (:axis constraints)]
320 axis
321 Vector3f/UNIT_X)
322 [limit-1 limit-2] (:limit constraints)
323 hinge-axis
324 (.mult
325 rotation
326 (blender-to-jme axis))]
327 (doto
328 (HingeJoint.
329 control-a
330 control-b
331 pivot-a
332 pivot-b
333 hinge-axis
334 hinge-axis)
335 (.setLimit limit-1 limit-2))))
337 (defmethod joint-dispatch :cone
338 [constraints control-a control-b pivot-a pivot-b rotation]
339 (let [limit-xz (:limit-xz constraints)
340 limit-xy (:limit-xy constraints)
341 twist (:twist constraints)]
343 (println-repl "creating CONE joint")
344 (println-repl rotation)
345 (println-repl
346 "UNIT_X --> " (.mult rotation (Vector3f. 1 0 0)))
347 (println-repl
348 "UNIT_Y --> " (.mult rotation (Vector3f. 0 1 0)))
349 (println-repl
350 "UNIT_Z --> " (.mult rotation (Vector3f. 0 0 1)))
351 (doto
352 (ConeJoint.
353 control-a
354 control-b
355 pivot-a
356 pivot-b
357 rotation
358 rotation)
359 (.setLimit (float limit-xz)
360 (float limit-xy)
361 (float twist)))))
363 (defn connect
364 "Create a joint between 'obj-a and 'obj-b at the location of
365 'joint. The type of joint is determined by the metadata on 'joint.
367 Here are some examples:
368 {:type :point}
369 {:type :hinge :limit [0 (/ Math/PI 2)] :axis (Vector3f. 0 1 0)}
370 (:axis defaults to (Vector3f. 1 0 0) if not provided for hinge joints)
372 {:type :cone :limit-xz 0]
373 :limit-xy 0]
374 :twist 0]} (use XZY rotation mode in blender!)"
375 [#^Node obj-a #^Node obj-b #^Node joint]
376 (let [control-a (.getControl obj-a RigidBodyControl)
377 control-b (.getControl obj-b RigidBodyControl)
378 joint-center (.getWorldTranslation joint)
379 joint-rotation (.toRotationMatrix (.getWorldRotation joint))
380 pivot-a (world-to-local obj-a joint-center)
381 pivot-b (world-to-local obj-b joint-center)]
383 (if-let [constraints
384 (map-vals
385 eval
386 (read-string
387 (meta-data joint "joint")))]
388 ;; A side-effect of creating a joint registers
389 ;; it with both physics objects which in turn
390 ;; will register the joint with the physics system
391 ;; when the simulation is started.
392 (do
393 (println-repl "creating joint between"
394 (.getName obj-a) "and" (.getName obj-b))
395 (joint-dispatch constraints
396 control-a control-b
397 pivot-a pivot-b
398 joint-rotation))
399 (println-repl "could not find joint meta-data!"))))
400 #+end_src
402 Creating joints is now a matter of applying =(connect)= to each joint
403 node.
405 #+name: joints-5
406 #+begin_src clojure
407 (defn joints!
408 "Connect the solid parts of the creature with physical joints. The
409 joints are taken from the \"joints\" node in the creature."
410 [#^Node creature]
411 (dorun
412 (map
413 (fn [joint]
414 (let [[obj-a obj-b] (joint-targets creature joint)]
415 (connect obj-a obj-b joint)))
416 (joints creature))))
417 #+end_src
420 ** Round 3
422 Now we can test the hand in all its glory.
424 #+name: test-3
425 #+begin_src clojure
426 (in-ns 'cortex.test.body)
428 (def debug-control
429 {"key-h" (fn [world val]
430 (if val (enable-debug world)))})
432 (defn test-three []
433 (world (nodify
434 [(doto (hand)
435 (physical!)
436 (joints!))
437 (floor)])
438 (merge standard-debug-controls debug-control
439 gravity-control)
440 (comp
441 #(Capture/captureVideo
442 % (File. "/home/r/proj/cortex/render/body/3"))
443 #(do (set-gravity % Vector3f/ZERO) %)
444 setup)
445 no-op))
446 #+end_src
448 =(physical!)= makes the hand solid, then =(joints!)= connects each
449 piece together.
451 #+begin_html
452 <div class="figure">
453 <center>
454 <video controls="controls" width="640">
455 <source src="../video/full-hand.ogg" type="video/ogg"
456 preload="none" poster="../images/aurellem-1280x480.png" />
457 </video>
458 </center>
459 <p>Now the hand is physical and has joints.</p>
460 </div>
461 #+end_html
463 The joints are visualized as green connections between each segment
464 for debug purposes. You can see that they correspond to the empty
465 nodes in the blender file.
467 * Wrap-Up!
469 It is convienent to combine =(physical!)= and =(joints!)= into one
470 function that completely creates the creature's physical body.
472 #+name: joints-6
473 #+begin_src clojure
474 (defn body!
475 "Endow the creature with a physical body connected with joints. The
476 particulars of the joints and the masses of each pody part are
477 determined in blender."
478 [#^Node creature]
479 (physical! creature)
480 (joints! creature))
481 #+end_src
483 * The Worm
485 Going forward, I will use a model that is less complicated than the
486 hand. It has two segments and one joint, and I call it the worm. All
487 of the senses described in the following posts will be applied to this
488 worm.
490 #+name: test-4
491 #+begin_src clojure
492 (in-ns 'cortex.test.body)
494 (defn worm []
495 (load-blender-model
496 "Models/test-creature/worm.blend"))
498 (defn worm-1 []
499 (let [timer (RatchetTimer. 60)]
500 (world
501 (nodify
502 [(doto (worm)
503 (body!))
504 (floor)])
505 (merge standard-debug-controls debug-control)
506 #(do
507 (speed-up %)
508 (light-up-everything %)
509 (.setTimer % timer)
510 (cortex.util/display-dialated-time % timer)
511 (Capture/captureVideo
512 % (File. "/home/r/proj/cortex/render/body/4")))
513 no-op)))
514 #+end_src
516 #+begin_html
517 <div class="figure">
518 <center>
519 <video controls="controls" width="640">
520 <source src="../video/worm-1.ogg" type="video/ogg"
521 preload="none" poster="../images/aurellem-1280x480.png" />
522 </video>
523 </center>
524 <p>This worm model will be the platform onto which future senses will
525 be grafted.</p>
526 </div>
527 #+end_html
529 * Headers
530 #+name: body-header
531 #+begin_src clojure
532 (ns cortex.body
533 "Assemble a physical creature using the definitions found in a
534 specially prepared blender file. Creates rigid bodies and joints so
535 that a creature can have a physical presense in the simulation."
536 {:author "Robert McIntyre"}
537 (:use (cortex world util sense))
538 (:use clojure.contrib.def)
539 (:import
540 (com.jme3.math Vector3f Quaternion Vector2f Matrix3f)
541 (com.jme3.bullet.joints
542 SixDofJoint Point2PointJoint HingeJoint ConeJoint)
543 com.jme3.bullet.control.RigidBodyControl
544 com.jme3.collision.CollisionResults
545 com.jme3.bounding.BoundingBox
546 com.jme3.scene.Node
547 com.jme3.scene.Geometry
548 com.jme3.bullet.collision.shapes.HullCollisionShape))
549 #+end_src
551 #+name: test-header
552 #+begin_src clojure
553 (ns cortex.test.body
554 (:use (cortex world util body))
555 (:import
556 (com.aurellem.capture Capture RatchetTimer)
557 (com.jme3.math Quaternion Vector3f ColorRGBA)
558 java.io.File))
559 #+end_src
561 * Source
562 - [[../src/cortex/body.clj][cortex.body]]
563 - [[../src/cortex/test/body.clj][cortex.test.body]]
564 - [[../assets/Models/test-creature/hand.blend][hand.blend]]
565 - [[../assets/Models/test-creature/palm.png][UV-map-1]]
566 - [[../assets/Models/test-creature/worm.blend][worm.blend]]
567 - [[../assets/Models/test-creature/retina-small.png][UV-map-1]]
568 - [[../assets/Models/test-creature/tip.png][UV-map-2]]
569 #+html: <ul> <li> <a href="../org/body.org">This org file</a> </li> </ul>
570 - [[http://hg.bortreb.com ][source-repository]]
572 * Next
573 The body I have made here exists without any senses or effectors. In
574 the [[./vision.org][next post]], I'll give the creature eyes.
576 * COMMENT Generate Source
577 #+begin_src clojure :tangle ../src/cortex/body.clj
578 <<body-header>>
579 <<body-1>>
580 <<joints-2>>
581 <<joints-3>>
582 <<joints-4>>
583 <<joints-5>>
584 <<joints-6>>
585 #+end_src
587 #+begin_src clojure :tangle ../src/cortex/test/body.clj
588 <<test-header>>
589 <<test-1>>
590 <<test-2>>
591 <<test-3>>
592 <<test-4>>
593 #+end_src