view org/body.org @ 282:2ad29b68ff22

saving before update of blender
author Robert McIntyre <rlm@mit.edu>
date Wed, 15 Feb 2012 14:09:20 -0700
parents c39b8b29a79e
children 23aadf376e9d
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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 # I'm a secret test! :P
16 ** Bag of Bones
18 How to create such a body? One option I ultimately rejected is to use
19 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
20 which describes the creature's entire body. To this you add an
21 skeleton which deforms this mesh. This technique is used extensively
22 to model humans and create realistic animations. It is hard to use for
23 my purposes because it is difficult to update the creature's Physics
24 Collision Mesh in tandem with its Geometric Mesh under the influence
25 of the armature. Withouth this the creature will not be able to grab
26 things in its environment, and it won't be able to tell where its
27 physical body is by using its eyes. Also, armatures do not specify
28 any rotational limits for a joint, making it hard to model elbows,
29 shoulders, etc.
31 ** EVE
33 Instead of using the human-like "deformable bag of bones" approach, I
34 decided to base my body plans on the robot EVE from the movie wall-E.
36 #+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.
37 [[../images/Eve.jpg]]
39 EVE's body is composed of several rigid components that are held
40 together by invisible joint constraints. This is what I mean by
41 "eve-like". The main reason that I use eve-style bodies is so that
42 there will be correspondence between the AI's vision and the physical
43 presence of its body. Each individual section is simulated by a
44 separate rigid body that corresponds exactly with its visual
45 representation and does not change. Sections are connected by
46 invisible joints that are well supported in jMonkyeEngine. Bullet, the
47 physics backend for jMonkeyEngine, can efficiently simulate hundreds
48 of rigid bodies connected by joints. Sections do not have to stay as
49 one piece forever; they can be dynamically replaced with multiple
50 sections to simulate splitting in two. This could be used to simulate
51 retractable claws or EVE's hands, which are able to coalece into one
52 object in the movie.
54 * Solidifying the Body
56 Here is a hand designed eve-style in blender.
58 #+attr_html: width="755"
59 [[../images/hand-screenshot0.png]]
61 If we load it directly into jMonkeyEngine, we get this:
63 #+name: test-1
64 #+begin_src clojure
65 (def hand-path "Models/test-creature/hand.blend")
67 (defn hand [] (load-blender-model hand-path))
69 (defn setup [world]
70 (let [cam (.getCamera world)]
71 (println-repl cam)
72 (.setLocation
73 cam (Vector3f.
74 -6.9015837, 8.644911, 5.6043186))
75 (.setRotation
76 cam
77 (Quaternion.
78 0.14046453, 0.85894054, -0.34301838, 0.3533118)))
79 (light-up-everything world)
80 (.setTimer world (RatchetTimer. 60))
81 world)
83 (defn test-one []
84 (world (hand)
85 standard-debug-controls
86 (comp
87 #(Capture/captureVideo
88 % (File. "/home/r/proj/cortex/render/body/1"))
89 setup)
90 no-op))
91 #+end_src
94 #+begin_src clojure :results silent
95 (.start (cortex.test.body/test-one))
96 #+end_src
98 #+begin_html
99 <div class="figure">
100 <center>
101 <video controls="controls" width="640">
102 <source src="../video/ghost-hand.ogg" type="video/ogg"
103 preload="none" poster="../images/aurellem-1280x480.png" />
104 </video>
105 </center>
106 <p>The hand model directly loaded from blender. It has no physical
107 presense in the simulation. </p>
108 </div>
109 #+end_html
111 You will notice that the hand has no physical presence -- it's a
112 hologram through which everything passes. Therefore, the first thing
113 to do is to make it solid. Blender has physics simulation on par with
114 jMonkeyEngine (they both use bullet as their physics backend), but it
115 can be difficult to translate between the two systems, so for now I
116 specify the mass of each object as meta-data in blender and construct
117 the physics shape based on the mesh in jMonkeyEngine.
119 #+name: body-1
120 #+begin_src clojure
121 (defn physical!
122 "Iterate through the nodes in creature and make them real physical
123 objects in the simulation."
124 [#^Node creature]
125 (dorun
126 (map
127 (fn [geom]
128 (let [physics-control
129 (RigidBodyControl.
130 (HullCollisionShape.
131 (.getMesh geom))
132 (if-let [mass (meta-data geom "mass")]
133 (do
134 (println-repl
135 "setting" (.getName geom) "mass to" (float mass))
136 (float mass))
137 (float 1)))]
138 (.addControl geom physics-control)))
139 (filter #(isa? (class %) Geometry )
140 (node-seq creature)))))
141 #+end_src
143 =physical!)= iterates through a creature's node structure, creating
144 CollisionShapes for each geometry with the mass specified in that
145 geometry's meta-data.
147 #+name: test-2
148 #+begin_src clojure
149 (in-ns 'cortex.test.body)
151 (def gravity-control
152 {"key-g" (fn [world _]
153 (set-gravity world (Vector3f. 0 -9.81 0)))
154 "key-u" (fn [world _] (set-gravity world Vector3f/ZERO))})
157 (defn floor []
158 (box 10 3 10 :position (Vector3f. 0 -10 0)
159 :color ColorRGBA/Gray :mass 0))
161 (defn test-two []
162 (world (nodify
163 [(doto (hand)
164 (physical!))
165 (floor)])
166 (merge standard-debug-controls gravity-control)
167 (comp
168 #(Capture/captureVideo
169 % (File. "/home/r/proj/cortex/render/body/2"))
170 #(do (set-gravity % Vector3f/ZERO) %)
171 setup)
172 no-op))
173 #+end_src
175 #+begin_html
176 <div class="figure">
177 <center>
178 <video controls="controls" width="640">
179 <source src="../video/crumbly-hand.ogg" type="video/ogg"
180 preload="none" poster="../images/aurellem-1280x480.png" />
181 </video>
182 </center>
183 <p>The hand now has a physical presence, but there is nothing to hold
184 it together.</p>
185 </div>
186 #+end_html
188 Now that's some progress.
190 * Joints
192 Obviously, an AI is not going to be doing much while lying in pieces
193 on the floor. So, the next step to making a proper body is to connect
194 those pieces together with joints. jMonkeyEngine has a large array of
195 joints available via bullet, such as Point2Point, Cone, Hinge, and a
196 generic Six Degree of Freedom joint, with or without spring
197 restitution.
199 Although it should be possible to specify the joints using blender's
200 physics system, and then automatically import them with jMonkeyEngine,
201 the support isn't there yet, and there are a few problems with bullet
202 itself that need to be solved before it can happen.
204 So, I will use the same system for specifying joints as I will do for
205 some senses. Each joint is specified by an empty node whose parent
206 has the name "joints". Their orientation and meta-data determine what
207 joint is created.
209 #+attr_html: width="755"
210 #+caption: Joints hack in blender. Each empty node here will be transformed into a joint in jMonkeyEngine
211 [[../images/hand-screenshot1.png]]
213 The empty node in the upper right, highlighted in yellow, is the
214 parent node of all the emptys which represent joints. The following
215 functions must do three things to translate these into real joints:
217 - Find the children of the "joints" node.
218 - Determine the two spatials the joint it meant to connect.
219 - Create the joint based on the meta-data of the empty node.
221 ** Finding the Joints
223 The higher order function =sense-nodes= from =cortex.sense= simplifies
224 the first task.
226 #+name: joints-2
227 #+begin_src clojure
228 (defvar
229 ^{:arglists '([creature])}
230 joints
231 (sense-nodes "joints")
232 "Return the children of the creature's \"joints\" node.")
233 #+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
419 ** Round 3
421 Now we can test the hand in all its glory.
423 #+name: test-3
424 #+begin_src clojure
425 (in-ns 'cortex.test.body)
427 (def debug-control
428 {"key-h" (fn [world val]
429 (if val (enable-debug world)))})
431 (defn test-three []
432 (world (nodify
433 [(doto (hand)
434 (physical!)
435 (joints!))
436 (floor)])
437 (merge standard-debug-controls debug-control
438 gravity-control)
439 (comp
440 #(Capture/captureVideo
441 % (File. "/home/r/proj/cortex/render/body/3"))
442 #(do (set-gravity % Vector3f/ZERO) %)
443 setup)
444 no-op))
445 #+end_src
447 =physical!= makes the hand solid, then =joints!= connects each
448 piece together.
450 #+begin_html
451 <div class="figure">
452 <center>
453 <video controls="controls" width="640">
454 <source src="../video/full-hand.ogg" type="video/ogg"
455 preload="none" poster="../images/aurellem-1280x480.png" />
456 </video>
457 </center>
458 <p>Now the hand is physical and has joints.</p>
459 </div>
460 #+end_html
462 The joints are visualized as green connections between each segment
463 for debug purposes. You can see that they correspond to the empty
464 nodes in the blender file.
466 * Wrap-Up!
468 It is convienent to combine =physical!= and =joints!= into one
469 function that completely creates the creature's physical body.
471 #+name: joints-6
472 #+begin_src clojure
473 (defn body!
474 "Endow the creature with a physical body connected with joints. The
475 particulars of the joints and the masses of each pody part are
476 determined in blender."
477 [#^Node creature]
478 (physical! creature)
479 (joints! creature))
480 #+end_src
482 * The Worm
484 Going forward, I will use a model that is less complicated than the
485 hand. It has two segments and one joint, and I call it the worm. All
486 of the senses described in the following posts will be applied to this
487 worm.
489 #+name: test-4
490 #+begin_src clojure
491 (in-ns 'cortex.test.body)
493 (defn worm []
494 (load-blender-model
495 "Models/test-creature/worm.blend"))
497 (defn worm-1 []
498 (let [timer (RatchetTimer. 60)]
499 (world
500 (nodify
501 [(doto (worm)
502 (body!))
503 (floor)])
504 (merge standard-debug-controls debug-control)
505 #(do
506 (speed-up %)
507 (light-up-everything %)
508 (.setTimer % timer)
509 (cortex.util/display-dialated-time % timer)
510 (Capture/captureVideo
511 % (File. "/home/r/proj/cortex/render/body/4")))
512 no-op)))
513 #+end_src
515 #+begin_html
516 <div class="figure">
517 <center>
518 <video controls="controls" width="640">
519 <source src="../video/worm-1.ogg" type="video/ogg"
520 preload="none" poster="../images/aurellem-1280x480.png" />
521 </video>
522 </center>
523 <p>This worm model will be the platform onto which future senses will
524 be grafted.</p>
525 </div>
526 #+end_html
528 * Headers
529 #+name: body-header
530 #+begin_src clojure
531 (ns cortex.body
532 "Assemble a physical creature using the definitions found in a
533 specially prepared blender file. Creates rigid bodies and joints so
534 that a creature can have a physical presense in the simulation."
535 {:author "Robert McIntyre"}
536 (:use (cortex world util sense))
537 (:use clojure.contrib.def)
538 (:import
539 (com.jme3.math Vector3f Quaternion Vector2f Matrix3f)
540 (com.jme3.bullet.joints
541 SixDofJoint Point2PointJoint HingeJoint ConeJoint)
542 com.jme3.bullet.control.RigidBodyControl
543 com.jme3.collision.CollisionResults
544 com.jme3.bounding.BoundingBox
545 com.jme3.scene.Node
546 com.jme3.scene.Geometry
547 com.jme3.bullet.collision.shapes.HullCollisionShape))
548 #+end_src
550 #+name: test-header
551 #+begin_src clojure
552 (ns cortex.test.body
553 (:use (cortex world util body))
554 (:import
555 (com.aurellem.capture Capture RatchetTimer)
556 (com.jme3.math Quaternion Vector3f ColorRGBA)
557 java.io.File))
558 #+end_src
560 * Source
561 - [[../src/cortex/body.clj][cortex.body]]
562 - [[../src/cortex/test/body.clj][cortex.test.body]]
563 - [[../assets/Models/test-creature/hand.blend][hand.blend]]
564 - [[../assets/Models/test-creature/palm.png][UV-map-1]]
565 - [[../assets/Models/test-creature/worm.blend][worm.blend]]
566 - [[../assets/Models/test-creature/retina-small.png][UV-map-1]]
567 - [[../assets/Models/test-creature/tip.png][UV-map-2]]
568 #+html: <ul> <li> <a href="../org/body.org">This org file</a> </li> </ul>
569 - [[http://hg.bortreb.com ][source-repository]]
571 * Next
572 The body I have made here exists without any senses or effectors. In
573 the [[./vision.org][next post]], I'll give the creature eyes.
575 * COMMENT Generate Source
576 #+begin_src clojure :tangle ../src/cortex/body.clj
577 <<body-header>>
578 <<body-1>>
579 <<joints-2>>
580 <<joints-3>>
581 <<joints-4>>
582 <<joints-5>>
583 <<joints-6>>
584 #+end_src
586 #+begin_src clojure :tangle ../src/cortex/test/body.clj
587 <<test-header>>
588 <<test-1>>
589 <<test-2>>
590 <<test-3>>
591 <<test-4>>
592 #+end_src