Returns the receiver's interpolation setting, which will be one of
<code>SWT.DEFAULT</code>, <code>SWT.NONE</code>,
<code>SWT.LOW</code> or <code>SWT.HIGH</code>.
@return the receiver's interpolation setting
@exception SWTException <ul>
<li>ERROR_GRAPHIC_DISPOSED - if the receiver has been disposed</li>
</ul>
Returns the receiver's interpolation setting, which will be one of <code>SWT.DEFAULT</code>, <code>SWT.NONE</code>, <code>SWT.LOW</code> or <code>SWT.HIGH</code>.
@return the receiver's interpolation setting
@exception SWTException <ul> <li>ERROR_GRAPHIC_DISPOSED - if the receiver has been disposed</li> </ul>
@since 3.1