LeeE > > 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. >
Good summary. Vivian ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
