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joint.sls
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joint.sls
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;; Copyright 2016 Eduardo Cavazos
;;
;; Licensed under the Apache License, Version 2.0 (the "License");
;; you may not use this file except in compliance with the License.
;; You may obtain a copy of the License at
;;
;; http://www.apache.org/licenses/LICENSE-2.0
;;
;; Unless required by applicable law or agreed to in writing, software
;; distributed under the License is distributed on an "AS IS" BASIS,
;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;; See the License for the specific language governing permissions and
;; limitations under the License.
(library (box2d-lite joint)
(export make-joint is-joint import-joint
joint-m joint-m-set!
joint-local-anchor-1 joint-local-anchor-1-set!
joint-local-anchor-2 joint-local-anchor-2-set!
joint-r1 joint-r1-set!
joint-r2 joint-r2-set!
joint-bias joint-bias-set!
joint-p joint-p-set!
joint-body-1 joint-body-1-set!
joint-body-2 joint-body-2-set!
joint-bias-factor joint-bias-factor-set!
joint-softness joint-softness-set!
create-joint
joint::set
joint::pre-step
joint::apply-impulse)
(import (rnrs)
(box2d-lite util define-record-type)
(box2d-lite vec)
(box2d-lite mat)
(box2d-lite body)
(box2d-lite world-parameters))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define-record-type++ joint
is-joint
import-joint
(fields (mutable m)
(mutable local-anchor-1)
(mutable local-anchor-2)
(mutable r1)
(mutable r2)
(mutable bias)
(mutable p)
(mutable body-1)
(mutable body-2)
(mutable bias-factor)
(mutable softness))
(methods (set joint::set)
(pre-step joint::pre-step)
(apply-impulse joint::apply-impulse)))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (create-joint)
(let ((j (make-joint #f #f #f #f #f #f #f #f #f #f #f)))
(is-joint j)
(j.p! (make-vec 0.0 0.0))
(j.bias-factor! 0.2)
(j.softness! 0.0)
j))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (joint::set j b1 b2 anchor)
(import-joint j)
(is-body body-1)
(is-body body-2)
(body-1! b1)
(body-2! b2)
(local-anchor-1!
(m*v (mat::transpose (angle->mat body-1.rotation))
(v- anchor body-1.position)))
(local-anchor-2!
(m*v (mat::transpose (angle->mat body-2.rotation))
(v- anchor body-2.position)))
(p! (make-vec 0.0 0.0))
(softness! 0.0)
(bias-factor! 0.2)
j)
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (joint::pre-step j inv-dt)
(import-joint j)
(is-body body-1)
(is-body body-2)
(is-vec r1)
(is-vec r2)
(is-vec bias)
(is-vec p)
(r1! (m*v (angle->mat body-1.rotation) local-anchor-1))
(r2! (m*v (angle->mat body-2.rotation) local-anchor-2))
(m!
(mat::invert
(m+m
(mat-by-rows (+ body-1.inv-mass body-2.inv-mass) 0.0
0.0 (+ body-1.inv-mass body-2.inv-mass))
(mat-by-rows (* body-1.inv-i r1.y r1.y ) (* body-1.inv-i r1.x r1.y -1)
(* body-1.inv-i r1.x r1.y -1) (* body-1.inv-i r1.x r1.x ))
(mat-by-rows (* body-2.inv-i r2.y r2.y ) (* body-2.inv-i r2.x r2.y -1)
(* body-2.inv-i r2.x r2.y -1) (* body-2.inv-i r2.x r2.x ))
(mat-by-rows softness 0
0 softness))))
(if (position-correction)
(bias! (n*v (* -1 bias-factor inv-dt)
(v- (v+ body-2.position r2)
(v+ body-1.position r1))))
(bias.set 0.0 0.0))
(if (warm-starting)
(begin
(body-1.velocity! (v- body-1.velocity (n*v body-1.inv-mass p)))
(body-1.angular-velocity!
(- body-1.angular-velocity (* body-1.inv-i (vxv r1 p))))
(body-2.velocity! (v+ body-2.velocity (n*v body-2.inv-mass p)))
(body-2.angular-velocity!
(+ body-2.angular-velocity (* body-2.inv-i (vxv r2 p)))))
(p.set 0.0 0.0)))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (joint::apply-impulse j)
(import-joint j)
(is-body body-1)
(is-body body-2)
(let ((dv (v- (v- (v+ body-2.velocity
(nxv body-2.angular-velocity
r2))
body-1.velocity)
(nxv body-1.angular-velocity r1))))
(let ((impulse (m*v m (v- (v- bias dv) (n*v softness p)))))
(body-1.velocity! (v- body-1.velocity (n*v body-1.inv-mass impulse)))
(body-1.angular-velocity!
(- body-1.angular-velocity (* body-1.inv-i (vxv r1 impulse))))
(body-2.velocity! (v+ body-2.velocity (n*v body-2.inv-mass impulse)))
(body-2.angular-velocity!
(+ body-2.angular-velocity (* body-2.inv-i (vxv r2 impulse))))
(p! (v+ p impulse)))))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
)