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
5 * in the Software without restriction, including without limitation the rights
6 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
7 * copies of the Software, and to permit persons to whom the Software is
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 void
preStep(cpRotaryLimitJoint * joint,cpFloat dt)25 preStep(cpRotaryLimitJoint *joint, cpFloat dt)
26 {
27 cpBody *a = joint->constraint.a;
28 cpBody *b = joint->constraint.b;
29
30 cpFloat dist = b->a - a->a;
31 cpFloat pdist = 0.0f;
32 if(dist > joint->max) {
33 pdist = joint->max - dist;
34 } else if(dist < joint->min) {
35 pdist = joint->min - dist;
36 }
37
38 // calculate moment of inertia coefficient.
39 joint->iSum = 1.0f/(a->i_inv + b->i_inv);
40
41 // calculate bias velocity
42 cpFloat maxBias = joint->constraint.maxBias;
43 joint->bias = cpfclamp(-bias_coef(joint->constraint.errorBias, dt)*pdist/dt, -maxBias, maxBias);
44
45 // If the bias is 0, the joint is not at a limit. Reset the impulse.
46 if(!joint->bias) joint->jAcc = 0.0f;
47 }
48
49 static void
applyCachedImpulse(cpRotaryLimitJoint * joint,cpFloat dt_coef)50 applyCachedImpulse(cpRotaryLimitJoint *joint, cpFloat dt_coef)
51 {
52 cpBody *a = joint->constraint.a;
53 cpBody *b = joint->constraint.b;
54
55 cpFloat j = joint->jAcc*dt_coef;
56 a->w -= j*a->i_inv;
57 b->w += j*b->i_inv;
58 }
59
60 static void
applyImpulse(cpRotaryLimitJoint * joint,cpFloat dt)61 applyImpulse(cpRotaryLimitJoint *joint, cpFloat dt)
62 {
63 if(!joint->bias) return; // early exit
64
65 cpBody *a = joint->constraint.a;
66 cpBody *b = joint->constraint.b;
67
68 // compute relative rotational velocity
69 cpFloat wr = b->w - a->w;
70
71 cpFloat jMax = joint->constraint.maxForce*dt;
72
73 // compute normal impulse
74 cpFloat j = -(joint->bias + wr)*joint->iSum;
75 cpFloat jOld = joint->jAcc;
76 if(joint->bias < 0.0f){
77 joint->jAcc = cpfclamp(jOld + j, 0.0f, jMax);
78 } else {
79 joint->jAcc = cpfclamp(jOld + j, -jMax, 0.0f);
80 }
81 j = joint->jAcc - jOld;
82
83 // apply impulse
84 a->w -= j*a->i_inv;
85 b->w += j*b->i_inv;
86 }
87
88 static cpFloat
getImpulse(cpRotaryLimitJoint * joint)89 getImpulse(cpRotaryLimitJoint *joint)
90 {
91 return cpfabs(joint->jAcc);
92 }
93
94 static const cpConstraintClass klass = {
95 (cpConstraintPreStepImpl)preStep,
96 (cpConstraintApplyCachedImpulseImpl)applyCachedImpulse,
97 (cpConstraintApplyImpulseImpl)applyImpulse,
98 (cpConstraintGetImpulseImpl)getImpulse,
99 };
100
101 cpRotaryLimitJoint *
cpRotaryLimitJointAlloc(void)102 cpRotaryLimitJointAlloc(void)
103 {
104 return (cpRotaryLimitJoint *)cpcalloc(1, sizeof(cpRotaryLimitJoint));
105 }
106
107 cpRotaryLimitJoint *
cpRotaryLimitJointInit(cpRotaryLimitJoint * joint,cpBody * a,cpBody * b,cpFloat min,cpFloat max)108 cpRotaryLimitJointInit(cpRotaryLimitJoint *joint, cpBody *a, cpBody *b, cpFloat min, cpFloat max)
109 {
110 cpConstraintInit((cpConstraint *)joint, &klass, a, b);
111
112 joint->min = min;
113 joint->max = max;
114
115 joint->jAcc = 0.0f;
116
117 return joint;
118 }
119
120 cpConstraint *
cpRotaryLimitJointNew(cpBody * a,cpBody * b,cpFloat min,cpFloat max)121 cpRotaryLimitJointNew(cpBody *a, cpBody *b, cpFloat min, cpFloat max)
122 {
123 return (cpConstraint *)cpRotaryLimitJointInit(cpRotaryLimitJointAlloc(), a, b, min, max);
124 }
125
126 cpBool
cpConstraintIsRotaryLimitJoint(const cpConstraint * constraint)127 cpConstraintIsRotaryLimitJoint(const cpConstraint *constraint)
128 {
129 return (constraint->klass == &klass);
130 }
131
132 cpFloat
cpRotaryLimitJointGetMin(const cpConstraint * constraint)133 cpRotaryLimitJointGetMin(const cpConstraint *constraint)
134 {
135 cpAssertHard(cpConstraintIsRotaryLimitJoint(constraint), "Constraint is not a rotary limit joint.");
136 return ((cpRotaryLimitJoint *)constraint)->min;
137 }
138
139 void
cpRotaryLimitJointSetMin(cpConstraint * constraint,cpFloat min)140 cpRotaryLimitJointSetMin(cpConstraint *constraint, cpFloat min)
141 {
142 cpAssertHard(cpConstraintIsRotaryLimitJoint(constraint), "Constraint is not a rotary limit joint.");
143 cpConstraintActivateBodies(constraint);
144 ((cpRotaryLimitJoint *)constraint)->min = min;
145 }
146
147 cpFloat
cpRotaryLimitJointGetMax(const cpConstraint * constraint)148 cpRotaryLimitJointGetMax(const cpConstraint *constraint)
149 {
150 cpAssertHard(cpConstraintIsRotaryLimitJoint(constraint), "Constraint is not a rotary limit joint.");
151 return ((cpRotaryLimitJoint *)constraint)->max;
152 }
153
154 void
cpRotaryLimitJointSetMax(cpConstraint * constraint,cpFloat max)155 cpRotaryLimitJointSetMax(cpConstraint *constraint, cpFloat max)
156 {
157 cpAssertHard(cpConstraintIsRotaryLimitJoint(constraint), "Constraint is not a rotary limit joint.");
158 cpConstraintActivateBodies(constraint);
159 ((cpRotaryLimitJoint *)constraint)->max = max;
160 }
161