Returns the alpha value at offset <code>x</code> in
scanline <code>y</code> in the receiver's alpha data.
The alpha value is between 0 (transparent) and
255 (opaque).
@param x the x coordinate of the pixel to get the alpha value of
@param y the y coordinate of the pixel to get the alpha value of
@return the alpha value at the given coordinates
@exception IllegalArgumentException <ul>
<li>ERROR_INVALID_ARGUMENT - if either argument is out of range</li>
</ul>
Returns the alpha value at offset <code>x</code> in scanline <code>y</code> in the receiver's alpha data. The alpha value is between 0 (transparent) and 255 (opaque).
@param x the x coordinate of the pixel to get the alpha value of @param y the y coordinate of the pixel to get the alpha value of @return the alpha value at the given coordinates
@exception IllegalArgumentException <ul> <li>ERROR_INVALID_ARGUMENT - if either argument is out of range</li> </ul>