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I've noticed that when driving at night, when the road surface is dry, my headlights appear to illuminate much further than when the road surface is wet. I presume that this is due to the differences in how my headlights is being reflected under wet and dry conditions.

In dry conditions, my headlight will reflect in a diffuse way, producing producing enough scatter to allow me to see the texture of the road for quite a long distance. In the wet however, the thin layer of water over the road surface, combined with the shallow angle of incidence, causes the light from my headlights to be reflected in a specular way and not back scattered to me.

Thinking about this, I realised that I can't remember ever having seen this effect being reproduced in a game.

  • Has this wet/dry effect been implemented in any game?

    • If so, what is the name of the technique used to produce the effect?
    • If not, could this effect be produced without ray-tracing?
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  • \$\begingroup\$ I don't have a name handy, but it's been done. Setting a parameter to control specular and the contribution of a reflection, just like you're describing. It's one of those effects that are best when you don't notice them, so you may not have noticed =) \$\endgroup\$
    – Patrick Hughes
    Feb 17, 2012 at 1:37
  • \$\begingroup\$ @PatrickHughes - Thanks, if you can dig out the name of the technique and post that as your answer, I'd be happy to mark it as the accepted answer. I mostly play RPGs rather than driving games and I can't see the technique I describe in the GT5 video mentioned by bummzack, but in real life the effect can be really quite pronounced if you are looking for it. It's one of the less concious reasons we end up driving much slower at night in the wet, even if it has stopped raining. \$\endgroup\$
    – Mark Booth
    Feb 21, 2012 at 14:34

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I pretty sure such effects are already implemented in state of the art racing games. Look at the following video of GT5.. there's a change from a rainy to a dry night-scene, where you can clearly see that the view of the street is better when dry.

While I don't know the name of that effect (other than reflection/refraction), it is most certainly achieved using shaders. For a realistic simulation, you would need ray-tracing, but graphics in games trade realism for computation speed and use less sophisticated simulations. The goal is to make it look real (physically correct rendering doesn't really matter in a fast-paced game anyways).

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