 canvas, different algorithms can be
used to blend the pixels. The different values of <a href="dart-ui/BlendMode-class.html">BlendMode</a> specify
different such algorithms.</p>
<p>Each algorithm has two inputs, the <em>source</em>, which is the image being drawn,
and the <em>destination</em>, which is the image into which the source image is
being composited. The destination is often thought of as the <em>background</em>.
The source and destination both have four color channels, the red, green,
blue, and 