Package-level declarations

Reusable GLSL fragments that any program can splice into its fragment shader to make its own pixels modulate against the active sightline's depth cube. Mirrors earth.worldwind.layer.shadow.ShadowReceiverGlsl for sun shadows.

Contract for shader programs that splice in SightlineReceiverGlsl. Identity-keyed cache: earth.worldwind.draw.DrawableSightline allocates a fresh SightlineState every frame, so receivers compare the new state instance against the last one they uploaded and skip the work when they match (covers the within-frame "second program-bind sees the same state" case).

The GL uniform-location + upload machinery every SightlineReceiverProgram needs, factored out of the 3D-Tiles mesh + points programs that each copy-pasted the identical field block, init resolution, and loadEnabled/loadDisabled bodies. A program owns one instance, resolves it in initProgram, and forwards its interface methods to it (see SightlineReceiverProgram).

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).

Binds the sightline depth cube on unit 5 and uploads the sightline uniforms into program. Skips the work when there's no active sightline this frame (or in pick mode), and clears applySightline so receivers fall through to "no tint".