r buffer, or when the clip operation is not rectilinear
(e.g. because it is a rounded rectangle clip created by <a href="../../dart-ui/Canvas/clipRRect.html">clipRRect</a> or an
arbitrarily complicated path clip created by <a href="../../dart-ui/Canvas/clipPath.html">clipPath</a>), the edge of the
clip needs to be anti-aliased.</p>
<p>If two draw calls overlap at the edge of such a clipped region, without
using <a href="../../dart-ui/Canvas/saveLayer.html">saveLayer</a>, the first drawing will be anti-alias