public void setExternalOffset(int offset) {
        mExternalOffset = offset;
    }
Implementation of {@link StateDrawable} to draw a morphing marker symbol.
<p>
It's basically an implementation of an {@link Animatable} Drawable with the following details:
</p>
<ul>
<li>Animates from a circle shape to a "marker" shape just using a RoundRect</li>
<li>Animates color change from the normal state color to the pressed state color</li>
<li>Uses a {@link Path} to also serve as Outline for API>=21</li>
</ul>

@hide
app/src/main/java/com/duan/musicoco/view/discreteseekbar/internal/drawable/MarkerDrawable.java