The glow effect is not done in engine. Instead, in Asperate, where I make the art, I duplicate the layer which as the sprite on it, then on the lower of the two layers, I apply a blur effect. This causes the pixels around it to become a mix of the sprite and the clear area around it, so it looks like it is glowing. I know its not the most elegant solution, but it worked for this project because I have very few sprites. Hope this helps!