If you map the Out Alpha from the file node into a reverse node, then take the output from the reverse node into the Out Transparency of your material.
That's a nice trick - but it looks nothing like additive blend mode sorry. Anyone else want to give it a try? In max you just open the material editor, expand the extended paramaters and set the advanced transparency to 'Add'. Is there some equivilent flag buried somewhere in Maya?
Can anyone tell me how to set a material to additive transparency in Maya? I want to create a muzzle flash using a texture that has no alpha channel - just a white/yellow/red/black flame gradient. The black part of the material should render as transparent and the other colors should add to the colors behind them, just…