+ double vdelta = after->value - before->value;
+
+ if (vdelta == 0.0) {
+ return before->value;
+ }
+
+ double tdelta = x - before->when;
+ double trange = after->when - before->when;
+
+ if (_list.interpolation() == ControlList::Curved && after->coeff) {
+ ControlEvent* ev = after;
+ double x2 = x * x;
+ return ev->coeff[0] + (ev->coeff[1] * x) + (ev->coeff[2] * x2) + (ev->coeff[3] * x2 * x);
+ } else {
+ return before->value + (vdelta * (tdelta / trange));
+ }