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Fix T101848: Zeroed matrix converted to a quaternion results in rotation 

Re-order checks to ensure a zeroed matrix results in a quaternion
without rotation. Also avoid some redundant calculation where the
'trace' was calculated but not used, flip the scaling value early
on instead of negating the quaternion after calculating it.
This commit is contained in:
Campbell Barton 2022-11-09 10:18:05 +11:00
parent ee5b6f7150
commit 494385a5bc
Notes: blender-bot 2023-02-14 10:18:56 +01:00 
Referenced by issue #101848, matrix_world.to_quaternion() returns wrong rotation for 0 scaled matrices
2 changed files with 62 additions and 43 deletions
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89
source/blender/blenlib/intern/math_rotation.c
View File

@ -275,63 +275,66 @@ void mat3_normalized_to_quat_fast(float q[4], const float mat[3][3])
/* Caller must ensure matrices aren't negative for valid results, see: T24291, T94231. */
BLI_assert(!is_negative_m3(mat));
/* Check the trace of the matrix - bad precision if close to -1. */
const float trace = mat[0][0] + mat[1][1] + mat[2][2];
if (trace > 0) {
float s = 2.0f * sqrtf(1.0f + trace);
q[0] = 0.25f * s;
s = 1.0f / s;
q[1] = (mat[1][2] - mat[2][1]) * s;
q[2] = (mat[2][0] - mat[0][2]) * s;
q[3] = (mat[0][1] - mat[1][0]) * s;
}
else {
/* Find the biggest diagonal element to choose the best formula.
* Here trace should also be always >= 0, avoiding bad precision. */
if (mat[0][0] > mat[1][1] && mat[0][0] > mat[2][2]) {
float s = 2.0f * sqrtf(1.0f + mat[0][0] - mat[1][1] - mat[2][2]);
/* Method outlined by Mike Day, ref: https://math.stackexchange.com/a/3183435/220949
* with an additional `sqrtf(..)` for higher precision result.
* Removing the `sqrt` causes tests to fail unless the precision is set to 1e-6 or larger. */
if (mat[2][2] < 0.0f) {
if (mat[0][0] > mat[1][1]) {
const float trace = 1.0f + mat[0][0] - mat[1][1] - mat[2][2];
float s = 2.0f * sqrtf(trace);
if (mat[1][2] < mat[2][1]) {
/* Ensure W is non-negative for a canonical result. */
s = -s;
}
q[1] = 0.25f * s;
s = 1.0f / s;
q[0] = (mat[1][2] - mat[2][1]) * s;
q[2] = (mat[1][0] + mat[0][1]) * s;
q[2] = (mat[0][1] + mat[1][0]) * s;
q[3] = (mat[2][0] + mat[0][2]) * s;
}
else if (mat[1][1] > mat[2][2]) {
float s = 2.0f * sqrtf(1.0f + mat[1][1] - mat[0][0] - mat[2][2]);
q[2] = 0.25f * s;
s = 1.0f / s;
q[0] = (mat[2][0] - mat[0][2]) * s;
q[1] = (mat[1][0] + mat[0][1]) * s;
q[3] = (mat[2][1] + mat[1][2]) * s;
}
else {
float s = 2.0f * sqrtf(1.0f + mat[2][2] - mat[0][0] - mat[1][1]);
q[3] = 0.25f * s;
const float trace = 1.0f - mat[0][0] + mat[1][1] - mat[2][2];
float s = 2.0f * sqrtf(trace);
if (mat[2][0] < mat[0][2]) {
/* Ensure W is non-negative for a canonical result. */
s = -s;
}
q[2] = 0.25f * s;
s = 1.0f / s;
q[0] = (mat[2][0] - mat[0][2]) * s;
q[1] = (mat[0][1] + mat[1][0]) * s;
q[3] = (mat[1][2] + mat[2][1]) * s;
}
}
else {
if (mat[0][0] < -mat[1][1]) {
const float trace = 1.0f - mat[0][0] - mat[1][1] + mat[2][2];
float s = 2.0f * sqrtf(trace);
if (mat[0][1] < mat[1][0]) {
/* Ensure W is non-negative for a canonical result. */
s = -s;
}
q[3] = 0.25f * s;
s = 1.0f / s;
q[0] = (mat[0][1] - mat[1][0]) * s;
q[1] = (mat[2][0] + mat[0][2]) * s;
q[2] = (mat[2][1] + mat[1][2]) * s;
q[2] = (mat[1][2] + mat[2][1]) * s;
}
/* Make sure W is non-negative for a canonical result. */
if (q[0] < 0) {
negate_v4(q);
else {
/* NOTE(@campbellbarton): A zero matrix will fall through to this block,
* needed so a zero scaled matrices to return a quaternion without rotation, see: T101848. */
const float trace = 1.0f + mat[0][0] + mat[1][1] + mat[2][2];
float s = 2.0f * sqrtf(trace);
q[0] = 0.25f * s;
s = 1.0f / s;
q[1] = (mat[1][2] - mat[2][1]) * s;
q[2] = (mat[2][0] - mat[0][2]) * s;
q[3] = (mat[0][1] - mat[1][0]) * s;
}
}
BLI_assert(!(q[0] < 0.0f));
normalize_qt(q);
}

16
source/blender/blenlib/tests/BLI_math_rotation_test.cc
View File

@ -3,6 +3,7 @@
#include "testing/testing.h"
#include "BLI_math_base.h"
#include "BLI_math_matrix.h"
#include "BLI_math_rotation.h"
#include "BLI_math_rotation.hh"
#include "BLI_math_vector.hh"
@ -138,6 +139,21 @@ TEST(math_rotation, quat_to_mat_to_quat_near_0001)
test_quat_to_mat_to_quat(0.30f, -0.030f, -0.30f, 0.95f);
}
/* A zeroed matrix converted to a quaternion and back should not add rotation, see: T101848 */
TEST(math_rotation, quat_to_mat_to_quat_zeroed_matrix)
{
float matrix_zeroed[3][3] = {{0.0f}};
float matrix_result[3][3];
float matrix_unit[3][3];
float out_quat[4];
unit_m3(matrix_unit);
mat3_normalized_to_quat(out_quat, matrix_zeroed);
quat_to_mat3(matrix_result, out_quat);
EXPECT_M3_NEAR(matrix_unit, matrix_result, FLT_EPSILON);
}
TEST(math_rotation, quat_split_swing_and_twist_negative)
{
const float input[4] = {-0.5f, 0, sqrtf(3) / 2, 0};