Fix the order in which additional transformations are applied in Matrix3 and Transform.

This is a part of the breaking changes proposed in PR #6865, solving the issue regarding the order of affine transformations described in #2565. This PR also fixes the affected code within Godot codebase. Includes improvements to documentation too.

Another change is, Matrix3::get_scale() will now return negative scaling when the determinant of the matrix is negative. The rationale behind this is simple: when performing a polar decomposition on a basis matrix M = R.S, we have to ensure that the determinant of R is +1, such that it is a proper rotation matrix (with no reflections) which can be represented by Euler angles or a quaternion.

Also replaced the few instances of float with real_t in Matrix3 and Transform.

Furthermore, this PR fixes an issue introduced due to the API breakage in #6865. Namely Matrix3::get_euler() now only works with proper rotation matrices. As a result, the code that wants to get the rotation portion of a transform needs to use Matrix3::get_rotation() introduced in this commit, which complements Matrix3::get_scaled(), providing both parts of the polar decomposition.

Finally, it is now possible to construct a rotation matrix from Euler angles using the new constructor Matrix3::Matrix3(const Vector3 &p_euler).

1 files changed, 7 insertions, 5 deletions

diff --git a/scene/3d/spatial.cpp b/scene/3d/spatial.cpp
index b5e80c48a1..50f9e45019 100644
--- a/scene/3d/spatial.cpp
+++ b/scene/3d/spatial.cpp
@@ -83,9 +83,9 @@ void Spatial::_notify_dirty() {
 
 
 void Spatial::_update_local_transform() const {
-
-	data.local_transform.basis.set_euler(data.rotation);
+	data.local_transform.basis = Matrix3();
 	data.local_transform.basis.scale(data.scale);
+	data.local_transform.basis.rotate(data.rotation);
 
 	data.dirty&=~DIRTY_LOCAL;
 }
@@ -376,7 +376,7 @@ void Spatial::_set_rotation_deg(const Vector3& p_euler_deg) {
 void Spatial::set_scale(const Vector3& p_scale){
 
 	if (data.dirty&DIRTY_VECTORS) {
-		data.rotation=data.local_transform.basis.get_euler();
+		data.rotation=data.local_transform.basis.get_rotation();
 		data.dirty&=~DIRTY_VECTORS;
 	}
 
@@ -398,7 +398,8 @@ Vector3 Spatial::get_rotation() const{
 
 	if (data.dirty&DIRTY_VECTORS) {
 		data.scale=data.local_transform.basis.get_scale();
-		data.rotation=data.local_transform.basis.get_euler();
+		data.rotation=data.local_transform.basis.get_rotation();
+
 		data.dirty&=~DIRTY_VECTORS;
 	}
 
@@ -422,7 +423,8 @@ Vector3 Spatial::get_scale() const{
 
 	if (data.dirty&DIRTY_VECTORS) {
 		data.scale=data.local_transform.basis.get_scale();
-		data.rotation=data.local_transform.basis.get_euler();
+		data.rotation=data.local_transform.basis.get_rotation();
+
 		data.dirty&=~DIRTY_VECTORS;
 	}