dali-physics/third-party/chipmunk2d/src/cpDampedRotarySpring.c

   1 /* Copyright (c) 2013 Scott Lembcke and Howling Moon Software
   2  *
   3  * Permission is hereby granted, free of charge, to any person obtaining a copy
   4  * of this software and associated documentation files (the "Software"), to deal
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   8  * furnished to do so, subject to the following conditions:
   9  *
  10  * The above copyright notice and this permission notice shall be included in
  11  * all copies or substantial portions of the Software.
  12  *
  13  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  14  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  15  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  16  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  17  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  18  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  19  * SOFTWARE.
  20  */
  21
  22 #include "chipmunk/chipmunk_private.h"
  23
  24 static cpFloat
  25 defaultSpringTorque(cpDampedRotarySpring *spring, cpFloat relativeAngle){
  26         return (relativeAngle - spring->restAngle)*spring->stiffness;
  27 }
  28
  29 static void
  30 preStep(cpDampedRotarySpring *spring, cpFloat dt)
  31 {
  32         cpBody *a = spring->constraint.a;
  33         cpBody *b = spring->constraint.b;
  34
  35         cpFloat moment = a->i_inv + b->i_inv;
  36         cpAssertSoft(moment != 0.0, "Unsolvable spring.");
  37         spring->iSum = 1.0f/moment;
  38
  39         spring->w_coef = 1.0f - cpfexp(-spring->damping*dt*moment);
  40         spring->target_wrn = 0.0f;
  41
  42         // apply spring torque
  43         cpFloat j_spring = spring->springTorqueFunc((cpConstraint *)spring, a->a - b->a)*dt;
  44         spring->jAcc = j_spring;
  45
  46         a->w -= j_spring*a->i_inv;
  47         b->w += j_spring*b->i_inv;
  48 }
  49
  50 static void applyCachedImpulse(cpDampedRotarySpring *spring, cpFloat dt_coef){}
  51
  52 static void
  53 applyImpulse(cpDampedRotarySpring *spring, cpFloat dt)
  54 {
  55         cpBody *a = spring->constraint.a;
  56         cpBody *b = spring->constraint.b;
  57
  58         // compute relative velocity
  59         cpFloat wrn = a->w - b->w;//normal_relative_velocity(a, b, r1, r2, n) - spring->target_vrn;
  60
  61         // compute velocity loss from drag
  62         // not 100% certain this is derived correctly, though it makes sense
  63         cpFloat w_damp = (spring->target_wrn - wrn)*spring->w_coef;
  64         spring->target_wrn = wrn + w_damp;
  65
  66         //apply_impulses(a, b, spring->r1, spring->r2, cpvmult(spring->n, v_damp*spring->nMass));
  67         cpFloat j_damp = w_damp*spring->iSum;
  68         spring->jAcc += j_damp;
  69
  70         a->w += j_damp*a->i_inv;
  71         b->w -= j_damp*b->i_inv;
  72 }
  73
  74 static cpFloat
  75 getImpulse(cpDampedRotarySpring *spring)
  76 {
  77         return spring->jAcc;
  78 }
  79
  80 static const cpConstraintClass klass = {
  81         (cpConstraintPreStepImpl)preStep,
  82         (cpConstraintApplyCachedImpulseImpl)applyCachedImpulse,
  83         (cpConstraintApplyImpulseImpl)applyImpulse,
  84         (cpConstraintGetImpulseImpl)getImpulse,
  85 };
  86
  87 cpDampedRotarySpring *
  88 cpDampedRotarySpringAlloc(void)
  89 {
  90         return (cpDampedRotarySpring *)cpcalloc(1, sizeof(cpDampedRotarySpring));
  91 }
  92
  93 cpDampedRotarySpring *
  94 cpDampedRotarySpringInit(cpDampedRotarySpring *spring, cpBody *a, cpBody *b, cpFloat restAngle, cpFloat stiffness, cpFloat damping)
  95 {
  96         cpConstraintInit((cpConstraint *)spring, &klass, a, b);
  97
  98         spring->restAngle = restAngle;
  99         spring->stiffness = stiffness;
 100         spring->damping = damping;
 101         spring->springTorqueFunc = (cpDampedRotarySpringTorqueFunc)defaultSpringTorque;
 102
 103         spring->jAcc = 0.0f;
 104
 105         return spring;
 106 }
 107
 108 cpConstraint *
 109 cpDampedRotarySpringNew(cpBody *a, cpBody *b, cpFloat restAngle, cpFloat stiffness, cpFloat damping)
 110 {
 111         return (cpConstraint *)cpDampedRotarySpringInit(cpDampedRotarySpringAlloc(), a, b, restAngle, stiffness, damping);
 112 }
 113
 114 cpBool
 115 cpConstraintIsDampedRotarySpring(const cpConstraint *constraint)
 116 {
 117         return (constraint->klass == &klass);
 118 }
 119
 120 cpFloat
 121 cpDampedRotarySpringGetRestAngle(const cpConstraint *constraint)
 122 {
 123         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 124         return ((cpDampedRotarySpring *)constraint)->restAngle;
 125 }
 126
 127 void
 128 cpDampedRotarySpringSetRestAngle(cpConstraint *constraint, cpFloat restAngle)
 129 {
 130         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 131         cpConstraintActivateBodies(constraint);
 132         ((cpDampedRotarySpring *)constraint)->restAngle = restAngle;
 133 }
 134
 135 cpFloat
 136 cpDampedRotarySpringGetStiffness(const cpConstraint *constraint)
 137 {
 138         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 139         return ((cpDampedRotarySpring *)constraint)->stiffness;
 140 }
 141
 142 void
 143 cpDampedRotarySpringSetStiffness(cpConstraint *constraint, cpFloat stiffness)
 144 {
 145         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 146         cpConstraintActivateBodies(constraint);
 147         ((cpDampedRotarySpring *)constraint)->stiffness = stiffness;
 148 }
 149
 150 cpFloat
 151 cpDampedRotarySpringGetDamping(const cpConstraint *constraint)
 152 {
 153         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 154         return ((cpDampedRotarySpring *)constraint)->damping;
 155 }
 156
 157 void
 158 cpDampedRotarySpringSetDamping(cpConstraint *constraint, cpFloat damping)
 159 {
 160         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 161         cpConstraintActivateBodies(constraint);
 162         ((cpDampedRotarySpring *)constraint)->damping = damping;
 163 }
 164
 165 cpDampedRotarySpringTorqueFunc
 166 cpDampedRotarySpringGetSpringTorqueFunc(const cpConstraint *constraint)
 167 {
 168         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 169         return ((cpDampedRotarySpring *)constraint)->springTorqueFunc;
 170 }
 171
 172 void
 173 cpDampedRotarySpringSetSpringTorqueFunc(cpConstraint *constraint, cpDampedRotarySpringTorqueFunc springTorqueFunc)
 174 {
 175         cpAssertHard(cpConstraintIsDampedRotarySpring(constraint), "Constraint is not a damped rotary spring.");
 176         cpConstraintActivateBodies(constraint);
 177         ((cpDampedRotarySpring *)constraint)->springTorqueFunc = springTorqueFunc;
 178 }