Atmospheric light scattering FAQ

Technically, Atmospheric Light Scattering, ALS, is a forward rendering framework for FlightGear, supplying a series of GLSL shader effects with consistent position-differential lighting and fogging for the whole scene.

Conceptually, ALS serves to make the Flightgear visuals realistic, committing the computing power of the graphics card predominantly to what a pilot gets to see most during flight, i.e. chiefly visuals in the air, from the cockpit. Primarily this is, as the name suggests light scattering in the atmosphere on the air and haze and visuals of sky and clouds, then hires dynamical texturing of the terrain and finally support for effects on 3d models. Things like aircraft shadows or secondary lights, the speciality of Project Rembrandt are minimally supported by ALS since they are relevant primarily on the ground and cost a lot of performance.

I am an aircraft developer, how do I make use of ALS effects?

Like any rendering framework, ALS has a simple default technique to render models. For more interesting effects (normal, reflection or dirt maps) it supports the Model-combined effect which is also supported by the other rendering frameworks (default and Project Rembrandt).

In addition, there is support for several ALS-specific effects: hires grain overlay, raindrop splashes, simple aircraft shadows, canopy glass and shading of the cockpit interior. These are documented in the ALS technical notes.

I am a custom scenery developer, how do I make use of ALS terrain texturing?

ALS has extensive support for Procedural Texturing which is xml-configurable in the (regional) materials file.