Well, not sure whether we're talking about the same thing.
Transparency, like displayed on the 1-2-3 picture isn't possible this way. Using a dithering filter could help making the picture look smoother all together, but won't change anything about the transparency issue. On any engine I've been messing around with, this kind of thing is best accomplished with texture-blending on the actual geomety, which AC does not support. Another solution would be changing the model's (which basically is just a plane) transparency parameter. I remember Toca tried this kind of stuff and it caused weird issues and therefore got dropped and therefore we've got no 'real' glass. ;) Another problem that can occur is that flat planes will not be rendered when applied close to geometry, which actually happens with sign models a lot. Maybe that's LOD related, maybe it's a z-fighting issue, maybe it's just a bug...
About the glass workaround shown above: That's quite a clever idea! You will get better results by using a higher resolution on the glass part, in other words you'll have to use non-uniformly (edited: un-uniformly) more space on the UV-map for this particular part of the model, like it's done with the sign-part on the dumpster model. Maybe you even use a seperated material for that one.
Transparency, like displayed on the 1-2-3 picture isn't possible this way. Using a dithering filter could help making the picture look smoother all together, but won't change anything about the transparency issue. On any engine I've been messing around with, this kind of thing is best accomplished with texture-blending on the actual geomety, which AC does not support. Another solution would be changing the model's (which basically is just a plane) transparency parameter. I remember Toca tried this kind of stuff and it caused weird issues and therefore got dropped and therefore we've got no 'real' glass. ;) Another problem that can occur is that flat planes will not be rendered when applied close to geometry, which actually happens with sign models a lot. Maybe that's LOD related, maybe it's a z-fighting issue, maybe it's just a bug...
About the glass workaround shown above: That's quite a clever idea! You will get better results by using a higher resolution on the glass part, in other words you'll have to use non-uniformly (edited: un-uniformly) more space on the UV-map for this particular part of the model, like it's done with the sign-part on the dumpster model. Maybe you even use a seperated material for that one.