Add method to compose an arbitrary number of affine ops

Author: urschrei

geo/CHANGES.md

@@ -39,6 +39,8 @@
 * Update rstar to v0.12.0
 * Implement `CoordsIter` for arrays and slices. This is useful when you'd like to use traits
   implemented for `CoordsIter` without re-allocating (e.g., creating a `MultiPoint`).
+* Add `compose_many` method to `AffineOps`
+  * <https://github.com/georust/geo/pull/1148>
 
 ## 0.27.0
 

geo/src/algorithm/affine_ops.rs

@@ -169,6 +169,32 @@ impl<T: CoordNum> AffineTransform<T> {
             ],
         ])
     }
+
+    /// Create a new affine transformation by composing an arbitrary number of `AffineTransform`s.
+    ///
+    /// This is a **cumulative** operation; the new transform is *added* to the existing transform.
+    /// ```
+    /// use geo::AffineTransform;
+    /// let mut transform = AffineTransform::identity();
+    ///
+    /// // create two transforms that cancel each other
+    /// let transform1 = AffineTransform::translate(1.0, 2.0);
+    /// let transform2 = AffineTransform::translate(-1.0, -2.0);
+    /// let transforms = vec![transform1, transform2];
+    ///
+    /// // apply them
+    /// let outcome = transform.compose_many(&transforms);
+    /// // we should be back to square one
+    /// assert!(outcome.is_identity());
+    /// ```
+    #[must_use]
+    pub fn compose_many(&self, transforms: &[Self]) -> Self {
+        self.compose(&transforms.iter().fold(
+            AffineTransform::default(),
+            |acc: AffineTransform<T>, transform| acc.compose(transform),
+        ))
+    }
+
     /// Create the identity matrix
     ///
     /// The matrix is: