Sightline
Per-frame snapshot of the active directional / omnidirectional sightline so receiver programs can sample the sightline depth cube in their own fragment shader (parallel to earth.worldwind.layer.shadow.ShadowState).
Populated by earth.worldwind.draw.DrawableSightline after its depth pass, before any receiver renders. Read by drawables that opt in via SightlineReceiverProgram and the applySightlineReceiverUniforms helper. null between frames and on frames without an enabled sightline; receivers must treat a null state as "no sightline".
Properties
cos(fieldOfView / 2) for the azimuth wedge; -1 (fov = 360) disables it.
Unit horizontal forward direction of the wedge in the local frame, (sin heading, cos heading). Irrelevant when the azimuth wedge is disabled (cosHalfFov = -1).
Occluded (out-of-line-of-sight) tint color. Premultiplied by the receiver.
World -> sightline-local transform (inv(centerTransform); local frame has Z = up).
sin(min(fieldOfView / 2, 90 deg)) capping elevation above the horizon; 1 disables it.
Visible (line-of-sight) tint color. Premultiplied by the receiver.