Open
Description
This loop seems quite suspicious:
weights[0] = 1.0f;
for (size_t p = 1; p <= degree; p++) {
ufbx_real prev = 0.0f;
ufbx_real g = 1.0f - ufbxi_nurbs_weight(&knots, knot - p + 1, p, u);
ufbx_real dg = 0.0f;
if (derivatives && p == degree) {
dg = ufbxi_nurbs_deriv(&knots, knot - p + 1, p);
}
for (size_t i = p; i > 0; i--) {
ufbx_real f = ufbxi_nurbs_weight(&knots, knot - p + i, p, u);
ufbx_real weight = weights[i - 1];
weights[i] = f*weight + g*prev;
if (derivatives && p == degree) {
ufbx_real df = ufbxi_nurbs_deriv(&knots, knot - p + i, p);
if (i < num_derivatives) {
derivatives[i] = df*weight - dg*prev;
}
dg = df;
}
prev = weight;
g = 1.0f - f;
}
weights[0] = g*prev;
if (derivatives && p == degree) {
derivatives[0] = -dg*prev;
}
}this would seem to be correct theoretically:
weights[0] = 1.0f;
for (size_t p = 1; p <= degree; p++) {
ufbx_real prev = 0.0f;
ufbx_real g = 1.0f - ufbxi_nurbs_weight(&knots, knot, p, u);
ufbx_real dg = 0.0f;
if (derivatives && p == degree) {
dg = ufbxi_nurbs_deriv(&knots, knot - p + 1, p);
}
for (size_t i = p; i > 0; i--) {
ufbx_real f = ufbxi_nurbs_weight(&knots, knot - p + i - 1, p, u);
ufbx_real weight = weights[i - 1];
weights[i] = f*weight + g*prev;
if (derivatives && p == degree) {
ufbx_real df = ufbxi_nurbs_deriv(&knots, knot - p + i - 1, p);
if (i < num_derivatives) {
derivatives[i] = df*weight - dg*prev;
}
dg = df;
}
prev = weight;
g = 1.0f - f;
}
weights[0] = g*prev;
if (derivatives && p == degree) {
derivatives[0] = -dg*prev;
}
}However, the previous formulation does pass all tests, which is curious. Ideally would need to make a test case that would break the old implementation, assuming that it is in fact broken.
Metadata
Metadata
Assignees
Labels
No labels