griefith/test2
1
0
Fork 0
Code Issues Pull Requests Actions 1 Packages Projects Releases Wiki Activity

Fix: Improve Obj importers parsing and detection of NURBS knot mode

Browse Source 
Reworks the implementation for how knots are interpreted when importing
NURBS in .obj format. It refactors each test into a separate function
and simplifies functions using a 'multiplicity sequence' which counts
repeated occurances of knot values (or their 'multiplicity'). Making
comparisons simpler, clearer, and with improved correctness.

With regard to regression tests behavior is almost the same, noticable
difference is consideration of cyclic. Allowing curves with multiplicity
at the endpoints to be cyclic (so Bezier curves can be cyclic given
one repeated point). Untested behavior may also have been 'refined'
(changed), but additional tests would be needed to identify those cases.

Pull Request: https://projects.blender.org/blender/blender/pulls/138778
This commit is contained in:
Mattias Fredriksson
2025-05-16 15:44:38 +02:00
committed by Hans Goudey
parent eb6fe4f6d7
commit bc0913240f
8 changed files with 175 additions and 75 deletions
Download Patch File Download Diff File Expand all files Collapse all files

215
source/blender/io/wavefront_obj/importer/obj_import_nurbs.cc
View File

@@ -82,6 +82,46 @@ static int8_t get_valid_nurbs_degree(const NurbsElement &element)
int8_t(degree);
}
/**
* Get the number of control points repeated for a cyclic curve given the multiplicity at the end
* of the knot vectors (multiplicity at both ends need to match).
*/
static int cyclic_repeated_points(const int8_t order, const int end_multiplicity)
{
/* Since multiplicity == order is considered 'cyclic' even if it is only C0 continuous in
* principle (it is technically discontinuous!), it needs to be clamped to 1.
*/
return std::max<int>(order - end_multiplicity, 1);
}
/**
* Compute the number of occurences of each unique knot value (so knot multiplicity), forming a
* sequence for which: sum(multiplicity) == knots.size().
*
* Example:
* Knots: [0, 0, 0, 0.1, 0.3, 0.4, 0.4, 0.4]
* Result: [3, 1, 1, 3]
*/
static Vector<int> calculate_multiplicity_sequence(const Span<float> knots)
{
Vector<int> multiplicity;
multiplicity.reserve(knots.size());
int m = 1;
for (const int64_t i : knots.index_range().drop_front(1)) {
/* Only consider multiplicity for exact matching values. */
if (knots[i - 1] == knots[i]) {
m++;
}
else {
multiplicity.append(m);
m = 1;
}
}
multiplicity.append(m);
return multiplicity;
}
void CurveFromGeometry::create_nurbs(Curve *curve, const OBJImportParams &import_params)
{
const NurbsElement &nurbs_geometry = curve_geometry_.nurbs_element_;
@@ -99,10 +139,12 @@ void CurveFromGeometry::create_nurbs(Curve *curve, const OBJImportParams &import
nurb->orderu = nurb->orderv = degree + 1;
nurb->resolu = nurb->resolv = curve->resolu;
const Vector<int> multiplicity = calculate_multiplicity_sequence(nurbs_geometry.parm);
nurb->flagu = this->detect_knot_mode(import_params,
degree,
nurbs_geometry.curv_indices,
nurbs_geometry.parm,
multiplicity,
nurbs_geometry.range);
if ((nurb->flagu & (CU_NURB_CUSTOM | CU_NURB_CYCLIC | CU_NURB_ENDPOINT)) == CU_NURB_CUSTOM) {
@@ -111,9 +153,11 @@ void CurveFromGeometry::create_nurbs(Curve *curve, const OBJImportParams &import
nurb->flagu &= ~CU_NURB_CUSTOM;
}
const int repeated_points = nurb->flagu & CU_NURB_CYCLIC ?
cyclic_repeated_points(nurb->orderu, multiplicity.first()) :
0;
const Span<int> indices = nurbs_geometry.curv_indices.as_span().slice(
nurbs_geometry.curv_indices.index_range().drop_front(nurb->flagu & CU_NURB_CYCLIC ? degree :
0));
nurbs_geometry.curv_indices.index_range().drop_back(repeated_points));
BKE_nurb_points_add(nurb, indices.size());
for (const int i : indices.index_range()) {
@@ -134,21 +178,103 @@ void CurveFromGeometry::create_nurbs(Curve *curve, const OBJImportParams &import
}
}
static bool detect_knot_mode_cyclic(const int degree,
const Span<int> indices,
const Span<float> knots)
static bool detect_clamped_endpoint(const int8_t degree, const Span<int> multiplicity)
{
const Span<int> indices_tail = indices.take_back(degree);
for (const int i : IndexRange(degree)) {
const int8_t order = degree + 1;
return multiplicity.first() == order && multiplicity.last() == order;
}
static bool detect_knot_mode_cyclic(const int8_t degree,
const Span<int> indices,
const Span<float> knots,
const Span<int> multiplicity)
{
constexpr float epsilon = 1e-7;
const int8_t order = degree + 1;
/* This is a good distinction between the 'cyclic' property and a true periodic NURBS curve. A
* periodic curve should be smooth to the degree - 1 derivative (which is the maximum possible).
* Allowing matching `multiplicity > 1` is not a periodic NURBS but can be considered cyclic.
*/
if (multiplicity.first() != multiplicity.last()) {
return false;
}
/* Multiplicity m is continous to the `degree - m` derivative and as such multiplcitiy == order
* is discontinous. By allowing it, clamped or Bezier curves can still be considered cyclic but
* ensure [here] that illogical `multiplicities > order` is not considered cyclic.
*/
if (multiplicity.first() > order || multiplicity.last() > order) {
return false;
}
const int repeated_points = cyclic_repeated_points(order, multiplicity.first());
const Span<int> indices_tail = indices.take_back(repeated_points);
for (const int64_t i : indices_tail.index_range()) {
if (indices[i] != indices_tail[i]) {
return false;
}
}
const Span<float> knots_tail = knots.take_back(2 * degree + 1);
for (const int i : IndexRange(degree - 1)) {
if (multiplicity.first() >= degree) {
/* There is no overlap in the knot spans. */
return true;
}
/* Ensure it matches on both of the knot spans adjacent to the start/end of the parameter range.
*/
const Span<float> knots_tail = knots.take_back(order + degree);
for (const int64_t i : knots_tail.index_range().drop_back(1)) {
const float head_span = knots[i + 1] - knots[i];
const float tail_span = knots_tail[i + 1] - knots_tail[i];
if (abs(head_span - tail_span) > 0.0001f) {
if (abs(head_span - tail_span) > epsilon) {
return false;
}
}
return true;
}
static bool detect_knot_mode_bezier(const int8_t degree, const Span<int> multiplicity)
{
const int8_t order = degree + 1;
if (multiplicity.first() != order || multiplicity.last() != order) {
return false;
}
for (const int m : multiplicity.drop_front(1).drop_back(1)) {
if (m != degree) {
return false;
}
}
return true;
}
static bool detect_knot_mode_uniform(const int8_t degree,
const Span<float> knots,
const Span<int> multiplicity,
bool clamped)
{
constexpr float epsilon = 1e-7;
/* Check if knot count matches multiplicity adjusted for clamped ends. For a uniform non-clamped
* curve, all multiplicity entries equals 1 and the array size should match.
*/
const int clamped_offset = clamped * degree;
if (knots.size() != multiplicity.size() - 2 * clamped_offset) {
return false;
}
/* Ensure it's not a single segment with clamped ends (it would be a Bezier segment). */
const Span<float> unclamped_knots = knots.drop_front(clamped_offset).drop_back(clamped_offset);
if (!unclamped_knots.size()) {
return false;
}
/* Verify spacing is uniform (excluding clamped ends). */
const float uniform_delta = unclamped_knots[1] - unclamped_knots[0];
for (const int64_t i : knots.index_range().drop_front(2)) {
if (abs((knots[i] - knots[i - 1]) - uniform_delta) < epsilon) {
return false;
}
}
@@ -159,61 +285,34 @@ short CurveFromGeometry::detect_knot_mode(const OBJImportParams &import_params,
const int8_t degree,
const Span<int> indices,
const Span<float> knots,
const float2 range)
const Span<int> multiplicity,
const float2 parameter_range)
{
short knot_mode = 0;
if (import_params.close_spline_loops && indices.size() > degree) {
SET_FLAG_FROM_TEST(knot_mode, detect_knot_mode_cyclic(degree, indices, knots), CU_NURB_CYCLIC);
SET_FLAG_FROM_TEST(
knot_mode, detect_knot_mode_cyclic(degree, indices, knots, multiplicity), CU_NURB_CYCLIC);
}
/* Figure out whether curve should have U endpoint flag set:
* the parameters should have at least (degree+1) values on each end,
* and their values should match curve range. */
bool do_endpoints = false;
const int8_t order = degree + 1;
if (knots.size() >= order * 2) {
do_endpoints = true;
for (int i = 0; i < order; ++i) {
if (abs(knots[i] - range.x) > 0.0001f || abs(knots.last(i) - range.y) > 0.0001f) {
do_endpoints = false;
break;
}
}
if (detect_knot_mode_bezier(degree, multiplicity)) {
/* Currently endpoint flag is not parsed for Bezier, mainly because a clamped Bezier curve in
* Blender is either:
* a) A valid Bezier curve for given degree/order with correct number of points to form one.
* b) Not a valid Bezier curve for given degree, last span/segment is of a lower degree Bezier.
*
* Set ENDPOINT to true since legacy Bezier NURBS only validates and compute knots if it
* contains order + 1 control points unless endpoint is set...?
*/
SET_FLAG_FROM_TEST(knot_mode, true, CU_NURB_ENDPOINT);
SET_FLAG_FROM_TEST(knot_mode, true, CU_NURB_BEZIER);
}
IndexRange inner_knots = knots.index_range();
if (do_endpoints) {
knot_mode |= CU_NURB_ENDPOINT;
inner_knots = inner_knots.size() > 2 * degree ?
inner_knots.drop_front(degree).drop_back(degree) :
IndexRange();
}
if (!inner_knots.is_empty()) {
const float first_step = knots[inner_knots.first() + 1] - knots[inner_knots.first()];
bool is_spacing_equal = true;
bool is_bezier_knot = degree > 1;
int repeats = 0;
for (const int i : inner_knots.drop_front(1).drop_back(1)) {
const float step = knots[i + 1] - knots[i];
if (abs(step - first_step) > 0.0001f) {
is_spacing_equal = false;
if (step == 0.0f) {
repeats++;
if (repeats > degree - 1) {
is_bezier_knot = false;
}
}
}
else if (repeats == degree - 1) {
repeats = 0;
}
else {
is_bezier_knot = false;
}
}
if (!is_spacing_equal) {
knot_mode |= is_bezier_knot ? CU_NURB_BEZIER : CU_NURB_CUSTOM;
}
else {
const bool clamped = detect_clamped_endpoint(degree, multiplicity);
SET_FLAG_FROM_TEST(knot_mode, clamped, CU_NURB_ENDPOINT);
SET_FLAG_FROM_TEST(knot_mode,
!detect_knot_mode_uniform(degree, knots, multiplicity, clamped),
CU_NURB_CUSTOM);
}
return knot_mode;
}

1
source/blender/io/wavefront_obj/importer/obj_import_nurbs.hh
View File

@@ -48,6 +48,7 @@ class CurveFromGeometry : NonMovable, NonCopyable {
int8_t degree,
Span<int> indices,
Span<float> knots,
Span<int> multiplicity,
float2 range);
};
} // namespace blender::io::obj

BIN
tests/files/io_tests/obj/nurbs_manual.obj (Stored with Git LFS)
View File

Binary file not shown.

10
tests/files/io_tests/obj/reference/all_curves_as_nurbs.txt
View File

@@ -57,13 +57,13 @@
==== Curves: 7
- Curve 'NurbsCircle' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:8x1 order:4x4 cyclic:True,False endp:False,False
- (11.463, 0.000, -1.000) w:1.000
- (10.463, 0.000, -1.000) w:1.000
- (10.463, 0.000, 0.000) w:1.000
...
- (12.463, 0.000, 1.000) w:1.000
- (12.463, 0.000, 0.000) w:1.000
- (12.463, 0.000, -1.000) w:1.000
...
- (10.463, 0.000, 0.000) w:1.000
- (10.463, 0.000, 1.000) w:1.000
- (11.463, 0.000, 1.000) w:1.000
- Curve 'NurbsCurve' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:4x1 order:4x4 cyclic:False,False endp:False,False
@@ -99,10 +99,10 @@
- Curve 'PolyCircle' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:4x1 order:2x2 cyclic:True,False endp:False,False
- (4.090, 0.000, -3.488) w:1.000
- (5.090, 0.000, -4.488) w:1.000
- (4.090, 0.000, -5.488) w:1.000
- (3.090, 0.000, -4.488) w:1.000
- (4.090, 0.000, -3.488) w:1.000
- Curve 'PolyCurve' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:3x1 order:2x2 cyclic:False,False endp:False,False

8
tests/files/io_tests/obj/reference/nurbs.txt
View File

@@ -1,13 +1,13 @@
==== Curves: 1
- Curve 'nurbs' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:9x1 order:4x4 cyclic:True,False endp:False,False
- (1.149, 0.964, -0.866) w:1.000
- (1.149, -0.964, 0.866) w:1.000
- (-1.500, -2.598, 0.000) w:1.000
...
- (0.260, -1.477, -0.866) w:1.000
- (-1.410, -0.513, 0.866) w:1.000
- (-1.500, 2.598, 0.000) w:1.000
...
- (-1.410, 0.513, -0.866) w:1.000
- (0.260, 1.477, 0.866) w:1.000
- (3.000, 0.000, 0.000) w:1.000
==== Objects: 1
- Obj 'nurbs' CURVE data:'nurbs'

2
tests/files/io_tests/obj/reference/nurbs_curves.txt
View File

@@ -15,10 +15,10 @@
- Curve 'NurbsCurveCyclic' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:4x1 order:4x4 cyclic:True,False endp:False,False
- (-6.000, -2.000, 0.000) w:1.000
- (-2.000, -2.000, 0.000) w:1.000
- (-2.000, 2.000, 0.000) w:1.000
- (-6.000, 2.000, 0.000) w:1.000
- (-6.000, -2.000, 0.000) w:1.000
- Curve 'NurbsCurveDiffWeights' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:4x1 order:4x4 cyclic:False,False endp:False,False

8
tests/files/io_tests/obj/reference/nurbs_cyclic.txt
View File

@@ -1,13 +1,13 @@
==== Curves: 1
- Curve 'nurbs_cyclic' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:28x1 order:4x4 cyclic:True,False endp:False,False
- (0.935, 0.000, 3.518) w:1.000
- (-0.050, 0.000, 2.052) w:1.000
- (1.001, 0.000, 1.462) w:1.000
...
- (2.591, 0.000, -0.795) w:1.000
- (4.054, 0.000, 0.651) w:1.000
- (3.281, 0.000, 3.043) w:1.000
...
- (4.054, 0.000, -0.651) w:1.000
- (2.591, 0.000, 0.795) w:1.000
- (1.500, 0.000, 0.000) w:1.000
==== Objects: 1
- Obj 'nurbs_cyclic' CURVE data:'nurbs_cyclic'

4
tests/files/io_tests/obj/reference/nurbs_manual.txt
View File

@@ -1,10 +1,10 @@
==== Curves: 4
- Curve 'Curve_Cyclic' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:4x1 order:4x4 cyclic:True,False endp:False,False
- (-2.000, 0.000, -2.000) w:1.000
- (-2.000, 0.000, 2.000) w:1.000
- (2.000, 0.000, 2.000) w:1.000
- (2.000, 0.000, -2.000) w:1.000
- (-2.000, 0.000, -2.000) w:1.000
- Curve 'Curve_Endpoints' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:5x1 order:4x4 cyclic:False,False endp:True,False
@@ -12,7 +12,7 @@
- (2.000, 0.000, 2.000) w:1.000
- (2.000, 0.000, -2.000) w:1.000
- (-2.000, 0.000, -2.000) w:1.000
- (-2.000, 0.000, 2.000) w:1.000
- (2.000, 0.000, 2.000) w:1.000
- Curve 'Curve_NonUniform_Parm' dim:3D resu:12 resv:12 splines:1
- spline type:NURBS pts:5x1 order:4x4 cyclic:False,False endp:False,False