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Fix polar decomposition in 2D.

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When performing polar decomposition in 2D as B = R.S, where R is rotation (with determinant +1) and S is scaling, use the convention that reflections are absorbed into S through a reflection around y axis.
In 3D, this is done by using a reflection along all three axes, but since the dimensionality is even in 2D, one axis needs to be chosen.

Fixes Matrix32::get_rotation and Matrix32::get_scale (which weren't properly fixed in #7445).
This commit is contained in:
Ferenc Arn 2017-03-29 11:51:31 -05:00
parent 000e873008
commit 97d510531a
1 changed files with 2 additions and 2 deletions
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4
core/math/math_2d.cpp
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@ -449,7 +449,7 @@ real_t Transform2D::get_rotation() const {
real_t det = basis_determinant(); real_t det = basis_determinant();
Transform2D m = orthonormalized(); Transform2D m = orthonormalized();
if (det < 0) { if (det < 0) {
m.scale_basis(Size2(-1, -1)); m.scale_basis(Size2(1, -1)); // convention to separate rotation and reflection for 2D is to absorb a flip along y into scaling.
} }
return Math::atan2(m[0].y, m[0].x); return Math::atan2(m[0].y, m[0].x);
} }
@ -477,7 +477,7 @@ Transform2D::Transform2D(real_t p_rot, const Vector2 &p_pos) {
Size2 Transform2D::get_scale() const { Size2 Transform2D::get_scale() const {
real_t det_sign = basis_determinant() > 0 ? 1 : -1; real_t det_sign = basis_determinant() > 0 ? 1 : -1;
return det_sign * Size2(elements[0].length(), elements[1].length()); return Size2(elements[0].length(), det_sign * elements[1].length());
} }
void Transform2D::scale(const Size2 &p_scale) { void Transform2D::scale(const Size2 &p_scale) {