1,360
edits
Atmospheric light scattering: Difference between revisions
Jump to navigation
Jump to search
→Light scattering during the day
| Line 59: | Line 59: | ||
== Light scattering during the day == | == Light scattering during the day == | ||
When the sun is high enough in the sky, the situation to render is as follows: | When the sun is high enough in the sky, the situation to render is as follows: All light intersects with the terrain with a comparatively large angle. This means that the curvature of earth doesn't make a difference - light intersecting with a level surface at 55 degrees isn't differently colored or much changed in intensity from light intersecting at 56 degrees, because the pathlengths through the atmosphere do not change much. This means that the whole scene can be rendered in spatially homogeneous light and all that matters is the vertical structure of light scattering and absorption in the atmosphere, which simplifies the rendering problem considerably. | ||
Thus, light penetrates the thin upper atmosphere, as it filters through, Rayleigh and some Mie scattering create the blue sky. Dependent on the model for the amount of high haze and water vapour to be specified by the weather system, this is handled by the skydome shader. | |||
As the light reaches the first significant cloud layer, light intensity is much reduced. As clouds are drawn outside the terrain and skydome shading codes, this can not be explicitly computed by the shader, neither is it computationally feasible to compute the shadow cast by each cloudlet by ray tracing in real time. Thus, the relevant parameters (<b>rendering/scene/scattering</b> for the light intensity reduction at the position of the aircraft and <b>/environment/surface/scattering</b> for the light reduction on the ground) must be modelled by the weather system (which knows the cloud layer position) and passed to the shaders. The visual difference between shaded terrain and unshaded terrain is illustrated by the following two screenshots: | As the light reaches the first significant cloud layer, light intensity is much reduced. As clouds are drawn outside the terrain and skydome shading codes, this can not be explicitly computed by the shader, neither is it computationally feasible to compute the shadow cast by each cloudlet by ray tracing in real time. Thus, the relevant parameters (<b>rendering/scene/scattering</b> for the light intensity reduction at the position of the aircraft and <b>/environment/surface/scattering</b> for the light reduction on the ground) must be modelled by the weather system (which knows the cloud layer position) and passed to the shaders. The visual difference between shaded terrain and unshaded terrain is illustrated by the following two screenshots: | ||
| Line 70: | Line 72: | ||
The altitude-dependent light reduction due to the clouds is the first instance of the <b>lightfield</b> technique, i.e. that the sunlight is represented as a series of functions r(x,y,z), g(x,y,z), b(x,y,z) in which the individual color channels are functions of vertex position in the scene. | The altitude-dependent light reduction due to the clouds is the first instance of the <b>lightfield</b> technique, i.e. that the sunlight is represented as a series of functions r(x,y,z), g(x,y,z), b(x,y,z) in which the individual color channels are functions of vertex position in the scene. | ||
== Light scattering at dawn / dusk == | == Light scattering at dawn / dusk == | ||