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cpDampedRotarySpring.c
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cpDampedRotarySpring.c
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/* Copyright (c) 2013 Scott Lembcke and Howling Moon Software
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "chipmunk/chipmunk_private.h"
static cpFloat
defaultSpringTorque(cpDampedRotarySpring *spring, cpFloat relativeAngle){
return (relativeAngle - spring->restAngle)*spring->stiffness;
}
static void
preStep(cpDampedRotarySpring *spring, cpFloat dt)
{
cpBody *a = spring->constraint.a;
cpBody *b = spring->constraint.b;
cpFloat moment = a->i_inv + b->i_inv;
cpAssertSoft(moment != 0.0, "Unsolvable spring.");
spring->iSum = 1.0f/moment;
spring->w_coef = 1.0f - cpfexp(-spring->damping*dt*moment);
spring->target_wrn = 0.0f;
// apply spring torque
cpFloat j_spring = spring->springTorqueFunc((cpConstraint *)spring, a->a - b->a)*dt;
spring->jAcc = j_spring;
a->w -= j_spring*a->i_inv;
b->w += j_spring*b->i_inv;
}
static void applyCachedImpulse(cpDampedRotarySpring *spring, cpFloat dt_coef){}
static void
applyImpulse(cpDampedRotarySpring *spring, cpFloat dt)
{
cpBody *a = spring->constraint.a;
cpBody *b = spring->constraint.b;
// compute relative velocity
cpFloat wrn = a->w - b->w;//normal_relative_velocity(a, b, r1, r2, n) - spring->target_vrn;
// compute velocity loss from drag
// not 100% certain this is derived correctly, though it makes sense
cpFloat w_damp = (spring->target_wrn - wrn)*spring->w_coef;
spring->target_wrn = wrn + w_damp;
//apply_impulses(a, b, spring->r1, spring->r2, cpvmult(spring->n, v_damp*spring->nMass));
cpFloat j_damp = w_damp*spring->iSum;
spring->jAcc += j_damp;
a->w += j_damp*a->i_inv;
b->w -= j_damp*b->i_inv;
}
static cpFloat
getImpulse(cpDampedRotarySpring *spring)
{
return spring->jAcc;
}
static const cpConstraintClass klass = {
(cpConstraintPreStepImpl)preStep,
(cpConstraintApplyCachedImpulseImpl)applyCachedImpulse,
(cpConstraintApplyImpulseImpl)applyImpulse,
(cpConstraintGetImpulseImpl)getImpulse,
};
cpDampedRotarySpring *
cpDampedRotarySpringAlloc(void)
{
return (cpDampedRotarySpring *)cpcalloc(1, sizeof(cpDampedRotarySpring));
}
cpDampedRotarySpring *
cpDampedRotarySpringInit(cpDampedRotarySpring *spring, cpBody *a, cpBody *b, cpFloat restAngle, cpFloat stiffness, cpFloat damping)
{
cpConstraintInit((cpConstraint *)spring, &klass, a, b);
spring->restAngle = restAngle;
spring->stiffness = stiffness;
spring->damping = damping;
spring->springTorqueFunc = (cpDampedRotarySpringTorqueFunc)defaultSpringTorque;
spring->jAcc = 0.0f;
return spring;
}
cpConstraint *
cpDampedRotarySpringNew(cpBody *a, cpBody *b, cpFloat restAngle, cpFloat stiffness, cpFloat damping)
{
return (cpConstraint *)cpDampedRotarySpringInit(cpDampedRotarySpringAlloc(), a, b, restAngle, stiffness, damping);
}
cpBool
cpConstraintIsDampedRotarySpring(const cpConstraint *constraint)
{
return (constraint->klass == &klass);
}
cpFloat
cpDampedRotarySpringGetRestAngle(const cpConstraint *constraint)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
return ((cpDampedRotarySpring *)constraint)->restAngle;
}
void
cpDampedRotarySpringSetRestAngle(cpConstraint *constraint, cpFloat restAngle)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
cpConstraintActivateBodies(constraint);
((cpDampedRotarySpring *)constraint)->restAngle = restAngle;
}
cpFloat
cpDampedRotarySpringGetStiffness(const cpConstraint *constraint)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
return ((cpDampedRotarySpring *)constraint)->stiffness;
}
void
cpDampedRotarySpringSetStiffness(cpConstraint *constraint, cpFloat stiffness)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
cpConstraintActivateBodies(constraint);
((cpDampedRotarySpring *)constraint)->stiffness = stiffness;
}
cpFloat
cpDampedRotarySpringGetDamping(const cpConstraint *constraint)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
return ((cpDampedRotarySpring *)constraint)->damping;
}
void
cpDampedRotarySpringSetDamping(cpConstraint *constraint, cpFloat damping)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
cpConstraintActivateBodies(constraint);
((cpDampedRotarySpring *)constraint)->damping = damping;
}
cpDampedRotarySpringTorqueFunc
cpDampedRotarySpringGetSpringTorqueFunc(const cpConstraint *constraint)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
return ((cpDampedRotarySpring *)constraint)->springTorqueFunc;
}
void
cpDampedRotarySpringSetSpringTorqueFunc(cpConstraint *constraint, cpDampedRotarySpringTorqueFunc springTorqueFunc)
{
cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
cpConstraintActivateBodies(constraint);
((cpDampedRotarySpring *)constraint)->springTorqueFunc = springTorqueFunc;
}