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Fix CMatrix<T>::getScale returning negative scale (#15687)

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Lars Müller 2025-01-18 00:27:27 +01:00 • committed by GitHub
parent c8b5e3b741
commit 8719a816e7
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3 changed files with 29 additions and 58 deletions
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42
irr/include/matrix4.h
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@ -782,7 +782,7 @@ inline CMatrix4<T> &CMatrix4<T>::setScale(const vector3d<T> &scale)
return *this;
}
//! Returns the absolute values of the scales of the matrix.
//! Returns the absolute values of the scales of the 3x3 submatrix.
/**
Note: You only get back original values if the matrix only set the scale.
Otherwise the result is a scale you can use to normalize the matrix axes,
@ -791,19 +791,15 @@ but it's usually no longer what you did set with setScale.
template <class T>
inline vector3d<T> CMatrix4<T>::getScale() const
{
// See http://www.robertblum.com/articles/2005/02/14/decomposing-matrices
// Deal with the 0 rotation case first
// Prior to Irrlicht 1.6, we always returned this value.
if (core::iszero(M[1]) && core::iszero(M[2]) &&
core::iszero(M[4]) && core::iszero(M[6]) &&
core::iszero(M[8]) && core::iszero(M[9]))
return vector3d<T>(M[0], M[5], M[10]);
// We have to do the full calculation.
return vector3d<T>(sqrtf(M[0] * M[0] + M[1] * M[1] + M[2] * M[2]),
sqrtf(M[4] * M[4] + M[5] * M[5] + M[6] * M[6]),
sqrtf(M[8] * M[8] + M[9] * M[9] + M[10] * M[10]));
auto row_vector_length = [this](int col) {
int i = 4 * col;
return sqrtf(M[i] * M[i] + M[i+1] * M[i+1] + M[i+2] * M[i+2]);
};
return {
row_vector_length(0),
row_vector_length(1),
row_vector_length(2),
};
}
template <class T>
@ -891,7 +887,7 @@ inline core::vector3d<T> CMatrix4<T>::getRotationDegrees(const vector3d<T> &scal
//! Returns a rotation that is equivalent to that set by setRotationDegrees().
template <class T>
inline core::vector3d<T> CMatrix4<T>::getRotationDegrees() const
inline vector3d<T> CMatrix4<T>::getRotationDegrees() const
{
// Note: Using getScale() here make it look like it could do matrix decomposition.
// It can't! It works (or should work) as long as rotation doesn't flip the handedness
@ -899,21 +895,7 @@ inline core::vector3d<T> CMatrix4<T>::getRotationDegrees() const
// crossproduct of first 2 axes to direction of third axis, but TODO)
// And maybe it should also offer the solution for the simple calculation
// without regarding scaling as Irrlicht did before 1.7
core::vector3d<T> scale(getScale());
// We assume the matrix uses rotations instead of negative scaling 2 axes.
// Otherwise it fails even for some simple cases, like rotating around
// 2 axes by 180° which getScale thinks is a negative scaling.
if (scale.Y < 0 && scale.Z < 0) {
scale.Y = -scale.Y;
scale.Z = -scale.Z;
} else if (scale.X < 0 && scale.Z < 0) {
scale.X = -scale.X;
scale.Z = -scale.Z;
} else if (scale.X < 0 && scale.Y < 0) {
scale.X = -scale.X;
scale.Y = -scale.Y;
}
vector3d<T> scale(getScale());
return getRotationDegrees(scale);
}