ShadowCasterSink

The palette is not optional in spirit, for the reason scatter below states about the wind: handing the depth pass a different deformation from the colour pass is how a shadow comes loose from its caster. A skinned character submitted through mesh does not drift slightly — it casts its bind pose, so a running figure throws the shadow of a statue.

Sixteen floats a joint, column-major, exactly as Skeleton.palette produces.

Not optional in spirit, for the reason scatter gives about the wind: a batch whose depth pass read a different placement casts shadows that have come loose from the things casting them — and a batch submitted through mesh instead casts one shadow, from whichever matrix happened to be bound, with the other twenty-nine missing entirely.

Optional in the type, and only because this interface is implemented outwards. A consumer's own sinks and its test doubles satisfy this type, so a required member added in a minor stops every one of them compiling — which is what happened: 3.29.0 broke three test doubles in a consumer that has no instanced batches at all. The renderer always supplies it, so sink.instanced?.(batch, data) never actually skips, and a consumer written before instanced draws existed has nothing to declare through it.

The wind and press arguments are the same values the matching drawScatter receives, and they are not optional in spirit: handing the depth pass a different gust from the colour pass is how a shadow comes loose from its caster. Positional rather than a bundled object, so a per-frame call site allocates nothing.