Additive and multiplicative blend modes can be nice to keep for some cheating / NPR stuff.

@paul szajner (szap) these modes can still be achieve using a combination of transparent and emission node. Also using the shader to rgba node to transfer their color in a NPR way is better as it clearly shows that this is incompatible with cycles.

@Brecht Van Lommel (brecht) @Dalai Felinto (dfelinto) @William Reynish (billreynish) If i'm supposed to remove the old Additive and Multiplicative blend mode, should I:

• A : Remove them and just let artists figure out what's wrong with the file (or at least do an alert in the bottom bar about the error). We did that at some point of 2.8.
• B : Create the replacement nodes inside versioning code.
• C : Create the replacement nodes inside tree evaluation code and keep the blend modes. But this add discrepancy between cycles and eevee.

@Clément Foucault (fclem) IMO we should ideally do B. If not, then we can also accept small incompatibilities between releases, although it needs to be mentioned in the release notes.

@Clément Foucault (fclem) B seems like the obvious choice here. Or more likely B + warnings for the few cases where you cannot convert them.

Ok going for B. But keep in mind that will break backward compatibility. Only way to keep it is to use C.