--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/trunk/chipmunkd/constraints/cpGearJoint.d	Thu Dec 02 22:26:04 2010 +0100
@@ -0,0 +1,119 @@
+
+// written in the D programming language
+
+module chipmunkd.constraints.cpGearJoint;
+
+import chipmunkd.chipmunk;
+import chipmunkd.constraints.util;
+
+//const cpConstraintClass *cpGearJointGetClass();
+
+struct cpGearJoint {
+	cpConstraint constraint;
+	cpFloat phase, ratio;
+	cpFloat ratio_inv;
+	
+	cpFloat iSum;
+		
+	cpFloat bias;
+	cpFloat jAcc, jMax;
+}
+
+//cpGearJoint *cpGearJointAlloc(void);
+//cpGearJoint *cpGearJointInit(cpGearJoint *joint, cpBody *a, cpBody *b, cpFloat phase, cpFloat ratio);
+//cpConstraint *cpGearJointNew(cpBody *a, cpBody *b, cpFloat phase, cpFloat ratio);
+//
+//CP_DefineConstraintProperty(cpGearJoint, cpFloat, phase, Phase);
+//CP_DefineConstraintGetter(cpGearJoint, cpFloat, ratio, Ratio);
+//void cpGearJointSetRatio(cpConstraint *constraint, cpFloat value);
+
+// cpGearJoint.c ---------------------------------
+
+static void
+preStep(cpGearJoint *joint, cpFloat dt, cpFloat dt_inv)
+{
+	mixin(CONSTRAINT_BEGIN!("joint", "a", "b"));
+	
+	// calculate moment of inertia coefficient.
+	joint.iSum = 1.0f/(a.i_inv*joint.ratio_inv + joint.ratio*b.i_inv);
+	
+	// calculate bias velocity
+	cpFloat maxBias = joint.constraint.maxBias;
+	joint.bias = cpfclamp(-joint.constraint.biasCoef*dt_inv*(b.a*joint.ratio - a.a - joint.phase), -maxBias, maxBias);
+	
+	// compute max impulse
+	joint.jMax = mixin(J_MAX!("joint", "dt"));
+
+	// apply joint torque
+	cpFloat j = joint.jAcc;
+	a.w -= j*a.i_inv*joint.ratio_inv;
+	b.w += j*b.i_inv;
+}
+
+static void
+applyImpulse(cpGearJoint *joint)
+{
+	mixin(CONSTRAINT_BEGIN!("joint", "a", "b"));
+	
+	// compute relative rotational velocity
+	cpFloat wr = b.w*joint.ratio - a.w;
+	
+	// compute normal impulse	
+	cpFloat j = (joint.bias - wr)*joint.iSum;
+	cpFloat jOld = joint.jAcc;
+	joint.jAcc = cpfclamp(jOld + j, -joint.jMax, joint.jMax);
+	j = joint.jAcc - jOld;
+	
+	// apply impulse
+	a.w -= j*a.i_inv*joint.ratio_inv;
+	b.w += j*b.i_inv;
+}
+
+static cpFloat
+getImpulse(cpGearJoint *joint)
+{
+	return cpfabs(joint.jAcc);
+}
+
+static /+const+/ cpConstraintClass klass = {
+	cast(cpConstraintPreStepFunction)&preStep,
+	cast(cpConstraintApplyImpulseFunction)&applyImpulse,
+	cast(cpConstraintGetImpulseFunction)&getImpulse,
+};
+mixin(CP_DefineClassGetter!("cpGearJoint"));
+
+cpGearJoint *
+cpGearJointAlloc()
+{
+	return cast(cpGearJoint *)cpmalloc(cpGearJoint.sizeof);
+}
+
+cpGearJoint *
+cpGearJointInit(cpGearJoint *joint, cpBody *a, cpBody *b, cpFloat phase, cpFloat ratio)
+{
+	cpConstraintInit(cast(cpConstraint *)joint, &klass, a, b);
+	
+	joint.phase = phase;
+	joint.ratio = ratio;
+	joint.ratio_inv = 1.0f/ratio;
+	
+	joint.jAcc = 0.0f;
+	
+	return joint;
+}
+
+cpConstraint *
+cpGearJointNew(cpBody *a, cpBody *b, cpFloat phase, cpFloat ratio)
+{
+	return cast(cpConstraint *)cpGearJointInit(cpGearJointAlloc(), a, b, phase, ratio);
+}
+
+void
+cpGearJointSetRatio(cpConstraint *constraint, cpFloat value)
+{
+	//TODO:
+	//cpConstraintCheckCast(constraint, cpGearJoint);
+	(cast(cpGearJoint *)constraint).ratio = value;
+	(cast(cpGearJoint *)constraint).ratio_inv = 1.0f/value;
+	cpConstraintActivateBodies(constraint);
+}