- Separate specular hilights. Specular hilights are bright areas on the plane that simualte the refelction of the sun on a shiny surface. X-Plane has had specular hilights for a while (available by the "shiny" check-box in Plane-Maker or ATTR_shiny_rat for an OBJ). What's new is: while previously the hilights were modulated by a texture, they are now independent of the texture. This change means that even a black surface can look shiny now. Before the black surface would "tint" the hilight black, making it invisible. Now we can have a white hilight on a black surface for a glossy look.
- Per-pixel lighting (when shaders are on). Before the lighting calculations were performed on each vertex on a model, then the color from the lighting was interpolated. The problem with this is that if there is a very local lighting effect (like a specular hilight) that is smaller than one triangle, you can't see it (since we can only see the lighting at far apart vertices). With 930, the lighting calculations are done per pixel, making the lighting effects look smoother.
Next we have the same plane in 930 without shaders:
Note the increased brightness on the nacelles and fuselage. What's happening is the hilights are no longer modulated by the texture, so they show up a bit more.
Finally, the plane in 930 with shaders. Now the hilights look smoother and much brighter. This is because the hilights are calculated on a per-pixel basis. Note how the hilights are small - smaller than the triangle size on the engines. We didn't get the full "glare" effect before because the brightest part of the hilight did not land on a vertex at all, and was thus never seen.
Note that the change in specular hilight handling (moving to separate specular hilights) is a bit of a compatibility break. Previously authors could count on not having specular hilights on dark parts of a plane, even if they set the plane to be shiny.
I am not sure how we will ship the final version of 930. I have received very few (none, to be exact) complaints about dark surfaces appearing "too shiny", and a lot of users like the new shiny look.
The alternative to the current scheme (specular hilights are separate by default) is to have this be a selectable feature. Older planes would look the same as they always did, but planes would have to be modified to make them look truly shiny.