Fix Qua4f multiplication

Author: ctreffs

Sources/FirebladeMath/Quat/Quaternion+Multiplication.swift

@@ -33,8 +33,11 @@ public func multiply(_ lhs: Quat4f, _ rhs: Quat4f) -> Quat4f {
     #if FRB_MATH_USE_SIMD
     return Quat4f(storage: simd.simd_mul(lhs.storage, rhs.storage))
     #else
-    #warning("not implemented yet")
-    return Quat4f.identity
+    let n0 = rhs.x * lhs.x - rhs.y * lhs.y - rhs.z * lhs.z - rhs.w * lhs.w
+    let n1 = rhs.x * lhs.y + rhs.y * lhs.x - rhs.z * lhs.w + rhs.w * lhs.z
+    let n2 = rhs.x * lhs.z + rhs.y * lhs.w + rhs.z * lhs.x - rhs.w * lhs.y
+    let n3 = rhs.x * lhs.w - rhs.y * lhs.z + rhs.z * lhs.y + rhs.w * lhs.x
+    return Quat4f(n3, n2, n1, n0)
     #endif
 }
 

Tests/FirebladeMathTests/Mat4x4fTests.swift

@@ -374,11 +374,11 @@ class Mat4x4fTests: XCTestCase {
         let m1 = Mat4x4f(translation: [1, 2, 3])
         let mat00 = m0 * m1
 
-        var mat = multiply(mat00, Vec4f(78.0, 3.02, -32, 0.093))
-        XCTAssertEqualElements(mat.elements, [55.978_317, 62.363_155, -9.606_318, 0.093_000], accuracy: 1e-5) // FIXME: would like to have 1e-6
+        var mat = multiply(mat00, Vec4f(78.0, 3.02, -32, 1.0))
+        XCTAssertEqualElements(mat.elements, [56.224686, 62.507904, -6.2246857, 1.0], accuracy: 1e-5)
 
-        mat = mat00 * Vec4f(78.0, 3.02, -32, 0.093)
-        XCTAssertEqualElements(mat.elements, [55.978_317, 62.363_155, -9.606_318, 0.093_000], accuracy: 1e-5) // FIXME: would like to have 1e-6
+        mat = mat00 * Vec4f(78.0, 3.02, -32, 1.0)
+        XCTAssertEqualElements(mat.elements, [56.224686, 62.507904, -6.2246857, 1.0], accuracy: 1e-5)
     }
 
     func testInverse() {