On Wednesday 01 April 2009, Erik Hofman wrote: > Heiko Schulz wrote: > > I'm against this code- I can't really understand what's the > > intention of this code is- destroying glossiness? > > Only when it's foggy. On bright clear days it will shine like > before. The real intent is to make it a bit more realistic. > > > I would like to see a change of the colors depending of the > > clouds setting- I think I can remember that the color changed > > with the weather settings in plib-versions. Example: less > > glossiness and more greyish colors on thunderstorm/ rainy day > > While not this may not be exactly true all the time but using > METAR will update both visibility and cloud settings accordingly > (heavy clouds will only be possible in situations with reduced > visibility anyhow). > > Erik
As I understand it, and from my 3D experience, the specular light component should define the brightness of highlights, on shiny/glossy surfaces, of reflected light sources. In real life, things are illuminated by a combination of direct light, scattered light and caustic light (however, we can't do caustics). The light source dictates the total amount of light entering the atmosphere, which scatters some of the light, mostly in the blue part of the spectrum, producing the ambient light. What is left then makes up the direct light component. So, under a clear sky, the direct light should be a bit yellow and the ambient light should be a bit blue. In fog or clouds though, where the fog or cloud is thick enough to scatter _all_ the light, there should be no direct light but much more ambient light, which should also be whiter as it now includes all of the colours from the light source and not just some of the blue component. Where this becomes relevant to specular light is that with no direct light source, there's nothing to produce a specular highlight. Although when near the ground though, the sky will still be brighter than the ground, so then there will be a slight degree of direct light. The amount of specular then, should be dependent on the glossiness/shininess of the surface (to provide a reflective highlight in the first place) and the amount of direct light. If you're in a bank of fog, where the horizontal visibility is low, but the fog is only say, forty feet thick, you should still get specular affects when the sun is high in the sky. Under an overcast sky though, where you can't make out the sun through the fog/clouds, you should get very little specular even if the horizontal visibility is high because there's no direct light source to create the reflective highlight. Using values up to 45km seem way too high to me - perhaps ~2km high value might be more realistic. I mentioned 'caustics' earlier; this refers to secondary reflected light. You can see the effects of caustic illumination when you stick something non-reflective, next to a coloured surface - the side of the non-reflective object will be illuminated by the coloured light reflected from the coloured surface. Like I said though, this isn't really viable in RT rendering so perhaps the ambient level should just be increased a little to account for it, forgetting about the colour cast because over a large area of different coloured background and objects the caustic colours will average out. LeeE ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
