Merge pull request #101797 from TokageItLab/fix-quat-arc

Fix `Quaternion` arc constructor to check dot & Add test for same `Vector3`s

core/math/quaternion.h

@@ -141,16 +141,24 @@ struct [[nodiscard]] Quaternion {
 	}
 
 	Quaternion(const Vector3 &p_v0, const Vector3 &p_v1) { // Shortest arc.
-		Vector3 c = p_v0.cross(p_v1);
-
-		if (c.is_zero_approx()) {
-			Vector3 axis = p_v0.get_any_perpendicular();
+#ifdef MATH_CHECKS
+		ERR_FAIL_COND_MSG(p_v0.is_zero_approx() || p_v1.is_zero_approx(), "The vectors must not be zero.");
+#endif
+		constexpr real_t ALMOST_ONE = 1.0f - (real_t)CMP_EPSILON;
+		Vector3 n0 = p_v0.normalized();
+		Vector3 n1 = p_v1.normalized();
+		real_t d = n0.dot(n1);
+		if (abs(d) > ALMOST_ONE) {
+			if (d >= 0) {
+				return; // Vectors are same.
+			}
+			Vector3 axis = n0.get_any_perpendicular();
 			x = axis.x;
 			y = axis.y;
 			z = axis.z;
 			w = 0;
 		} else {
-			real_t d = p_v0.dot(p_v1);
+			Vector3 c = n0.cross(n1);
 			real_t s = Math::sqrt((1.0f + d) * 2.0f);
 			real_t rs = 1.0f / s;
 

tests/core/math/test_quaternion.h

@@ -263,6 +263,9 @@ TEST_CASE("[Quaternion] Construct Shortest Arc For 180 Degree Arc") {
 
 	// For the consistency of the rotation direction, they should be symmetrical to the plane.
 	CHECK(left_to_right.is_equal_approx(right_to_left.inverse()));
+
+	// If vectors are same, no rotation.
+	CHECK(Quaternion(diagonal_up, diagonal_up).is_equal_approx(Quaternion()));
 }
 
 TEST_CASE("[Quaternion] Get Euler Orders") {