One of the downsides of deferred rendering is it isn't very good at handling transparent surfaces. Since we have moved to a new forward renderer, one of my goals in Leadwerks 5 is to have easy hassle-free transparency with lighting and refraction that just works.
Pre-multiplied alpha provides a better blending equation than traditional alpha blending. I'm not going to go into the details here, but it makes it so the transparent surface can be brighter than the underlying surface, as you can see on the vehicle's windshield here:
I've been working for a while to build an automatic post-processing step into the engine that occurs when a transparency object is onscreen. If no transparent objects are onscreen, then the post-processing step can be skipped.
You can also call Camera::SetRefraction(false) and just use regular GPU-blended transparency with no fancy refraction of the background, but I plan to enable it by default.
To use this effect, there is absolutely nothing you have to do except to create a material, make it transparent, and apply it to a mesh somewhere.
auto mtl = CreateMaterial(); mtl->SetTransparent(true); mtl->SetColor(1,1,1,0.5);
The lower the alpha value of the material color, the more see-through it is. You can use an alpha value of zero to make a refractive predator-like effect.