--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/trunk/chipmunkd/constraints/cpSimpleMotor.d	Thu Dec 02 22:26:04 2010 +0100
@@ -0,0 +1,98 @@
+
+// written in the D programming language
+
+module chipmunkd.constraints.cpSimpleMotor;
+
+import chipmunkd.chipmunk;
+import chipmunkd.constraints.util;
+
+//const cpConstraintClass *cpSimpleMotorGetClass();
+
+struct cpSimpleMotor {
+	cpConstraint constraint;
+	cpFloat rate;
+	
+	cpFloat iSum;
+		
+	cpFloat jAcc, jMax;
+}
+
+//cpSimpleMotor *cpSimpleMotorAlloc(void);
+//cpSimpleMotor *cpSimpleMotorInit(cpSimpleMotor *joint, cpBody *a, cpBody *b, cpFloat rate);
+//cpConstraint *cpSimpleMotorNew(cpBody *a, cpBody *b, cpFloat rate);
+//
+//CP_DefineConstraintProperty(cpSimpleMotor, cpFloat, rate, Rate);
+
+// cpRotaryLimitJoint.c ---------------------------------
+
+static void
+preStep(cpSimpleMotor *joint, cpFloat dt, cpFloat dt_inv)
+{
+	mixin(CONSTRAINT_BEGIN!("joint", "a", "b"));
+	
+	// calculate moment of inertia coefficient.
+	joint.iSum = 1.0f/(a.i_inv + b.i_inv);
+	
+	// compute max impulse
+	joint.jMax = mixin(J_MAX!("joint", "dt"));
+
+	// apply joint torque
+	a.w -= joint.jAcc*a.i_inv;
+	b.w += joint.jAcc*b.i_inv;
+}
+
+static void
+applyImpulse(cpSimpleMotor *joint)
+{
+	mixin(CONSTRAINT_BEGIN!("joint", "a", "b"));
+	
+	// compute relative rotational velocity
+	cpFloat wr = b.w - a.w + joint.rate;
+	
+	// compute normal impulse	
+	cpFloat j = -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;
+	b.w += j*b.i_inv;
+}
+
+static cpFloat
+getImpulse(cpSimpleMotor *joint)
+{
+	return cpfabs(joint.jAcc);
+}
+
+static /+const+/ cpConstraintClass klass = {
+	cast(cpConstraintPreStepFunction)&preStep,
+	cast(cpConstraintApplyImpulseFunction)&applyImpulse,
+	cast(cpConstraintGetImpulseFunction)&getImpulse,
+};
+mixin(CP_DefineClassGetter!("cpSimpleMotor"));
+
+cpSimpleMotor *
+cpSimpleMotorAlloc()
+{
+	return cast(cpSimpleMotor *)cpmalloc(cpSimpleMotor.sizeof);
+}
+
+cpSimpleMotor *
+cpSimpleMotorInit(cpSimpleMotor *joint, cpBody *a, cpBody *b, cpFloat rate)
+{
+	cpConstraintInit(cast(cpConstraint *)joint, &klass, a, b);
+	
+	joint.rate = rate;
+	
+	joint.jAcc = 0.0f;
+	
+	return joint;
+}
+
+cpConstraint *
+cpSimpleMotorNew(cpBody *a, cpBody *b, cpFloat rate)
+{
+	return cast(cpConstraint *)cpSimpleMotorInit(cpSimpleMotorAlloc(), a, b, rate);
+}