Given a Texture and an
y coordinate this method will return a value between 0 and 255
corresponding to the alpha value of the pixel at that location in the Texture. If the coordinate
is out of bounds it will return null.
The x coordinate of the pixel within the Texture.
The y coordinate of the pixel within the Texture.
The unique string-based key of the Texture.
|frame||string | number||<optional>||
The string or index of the Frame.
A value between 0 and 255, or
null if the coordinates were out of bounds.