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Atmospheric light scattering: Difference between revisions
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→Light scattering at dawn / dusk
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Short of directly computing the light passing through the atmosphere, these effects can be taken into account by using lightfields, i.e. by changing the color and intensity of the sunlight dependent on the position and altitude of the illuminated vertex. However, even computing parametrized lightfields make a significant performance impact as compared to the rendering situation at noon. | Short of directly computing the light passing through the atmosphere, these effects can be taken into account by using lightfields, i.e. by changing the color and intensity of the sunlight dependent on the position and altitude of the illuminated vertex. However, even computing parametrized lightfields make a significant performance impact as compared to the rendering situation at noon. | ||
Unfortunately, the lightfield scheme used to render the light color combined with the scheme used to determine cloud shading is not guaranteed to give realistic effects. In reality for instance, a low sun can sometimes illuminate a layer from below. Whether this is possible or not depends on how far the layer extends - if it extends all the way to the horizon, it can never be illuminated from below, but if it terminates before, this is possible. It also depends on the terrain - there might be a chain of mountains far away which blocks the sun. In order to get the situation right, the weather system would have to be able to determine the cloud cover ~200 km away from the current position, but in Flightgear typically neither the terrain nor the weather at such distances is known. | |||
Another effect which is currently not addressed adequately is the inter-cloud shading (clouds casting shadows on other clouds). Due to the layer structure of clouds, at noon this is usually not a big issue and only the self-shading of clouds is relevant, but for a low sun inter-cloud shading (and fog being shaded by clouds) is often very pronounced in reality. | |||