XNA adding colors when overlap

I have sprite开发者_JS百科s that when they overlap I would like them to 'add' their colors rgb values to (potentially) go white, the sprites also have changin alpha values which should remain unchanged. I've already tried using all the spritebatch options alphablend, additive etc...

Is this possible through spritebatch or will i need a shader?

Thanks, Paul.

Using the Premultiplied Alpha scheme in XNA 4, you can do additive blending by having your texture drawn at 0 alpha. Because this means that there is 0 blocking done by the texture, and then the RGB is added to the pixels behind it, you get additive blending.

Just draw the texture with 0 alpha using the spritebatch mode 'Alphablend'. To lower the additivity, increase alpha. To make it less visible, lower RGB.

I highly suggest making sure any textures in your content have the option 'Premultiplied Alpha' ticked in their properties, if you use this.