Provide a pixel transform to render events

src/ol/transform.js

@@ -236,3 +236,7 @@ export function invert(transform) {
 export function determinant(mat) {
   return mat[0] * mat[3] - mat[1] * mat[2];
 }
+
+export function toString(mat) {
+  return 'matrix(' + mat.join(', ') + ')';
+}