(imported from here) So I've been thinking about the wierd "trippy wavey-shader" effect tdev tried using, and maybe you could use it to slimlate the "visible heat" you usually see on hot days. This effect could be combined with depth-of-field to make really distant objects appear distorted realistically. Also, expanding on that, you could refine the road reflectivity so that, with the waves enabled, the asphalt really far away will be dynamically "reflective" (like a mirage), or you could see the heat from a car exhaust on cold days.
