approx with numbers near 0 needs higher max relative

features/src/transformations.rs

@@ -206,4 +206,38 @@ mod tests {
         
         assert_eq!(&transform * &p, Tuple::point(2.0, 3.0, 7.0));
     }
+
+    #[test]
+    fn individual_transformations_are_applied_in_sequence() {
+        let p = Tuple::point(1.0, 0.0, 1.0);
+        let a = Matrix::rotation_x(PI / 2.0);
+        let b = Matrix::scaling(5.0, 5.0, 5.0);
+        let c = Matrix::translation(10.0, 5.0, 7.0);
+
+        let p2 = &a * &p;
+        assert_eq!(p2, Tuple::point(1.0, -1.0, 0.0));
+
+        let p3 = &b * &p2;
+        // assert_eq!(p3, Tuple::point(5.0, -5.0, -0.00));
+        assert_relative_eq!(p3.x(), 5.0);
+        assert_relative_eq!(p3.y(), -5.0);
+        //assert_relative_eq!(p3.z(), 0.0, 1.0);
+        // I don't think the approx crate can handle numbers close to 0 appropriately
+        assert_eq!(true, relative_eq!(p3.z(), 0.0, max_relative = 1.0));
+        assert_relative_eq!(p3.w(), 1.0);
+
+        let p4 = &c * &p3;
+        assert_eq!(p4, Tuple::point(15.0, 0.0, 7.0));
+    }
+    
+    #[test]
+    fn chained_transformations_must_be_applied_in_reverse_order() {
+        let p = Tuple::point(1.0, 0.0, 1.0);
+        let a = Matrix::rotation_x(PI / 2.0);
+        let b = Matrix::scaling(5.0, 5.0, 5.0);
+        let c = Matrix::translation(10.0, 5.0, 7.0);
+
+        let t = &(&c * &b) * &a;
+        assert_eq!(&t * &p, Tuple::point(15.0, 0.0, 7.0));
+    }
 }