mat/MeshSDF

Assign it to SDF objects with a geo/Material node. SDF objects already render without it, on these same defaults; this node is what makes the march tunable and adds the debug views. Every param is a uniform, so dragging one never recompiles the shader. Raise `maxStepsCount` when a shape shows holes or soft edges where the rays run out of steps, and lower it when a scene gets slow: the step-count debug view shows where the budget actually goes, silhouette rays being the expensive ones. Lower `surfaceDistance` for a crisper surface at the cost of more steps. `isoValue` moves which surface is drawn, so one tree can be looked at at several levels without touching it. It also carries the self-lighting the object gets from its own field: `shadowSoftness` for soft shadows where one part of the shape shadows another, on by default and scaling the width each light asks for with its own `softness`, and `aoStrength` for darkened creases, off by default. Both are per-object: neither sees any other object in the scene. `gridFiltering` is the one param that only some trees read: a field built from a volume (geo/SDFCreate) is a grid of voxels, and TRICUBIC reads between them with a continuous gradient, which is what removes the per-voxel faceting an imported model shows. A 2D field is not marched at all, it is painted as a distance-field visualization, so the only params it reads are `bandSpacing` and `isoValue`. `color`, `roughness`, `metallic` and `emissive` here are the DEFAULT surface, and an object that carries a shading record of its own overrides them: what a geo/MaterialAttributes wrote wins, per region of the field (see geo/SDFBoolean). Everything else on this node stays the object's, record or not. Drop a geo/Environment into the scene and SDF objects light from it like every other surface, with no wiring and without this node: the map is the scene's, so there is nothing here to point at it.

**Glass.** `transmission` above 0 lets light through the surface, with `ior`, `attenuationColor` and `attenuationDistance` describing the medium. At each pixel the light splits between a reflection and a refraction by the Fresnel term, so glass reflects mostly at grazing angles and shows what is behind it head on. The refracted ray crosses the object's own field to its far side and leaves toward the scene environment, so what shows through is the environment, not the rest of the scene; with no geo/Environment there is nothing to see through it. Turning `transmission` up from 0 regenerates the shader once, and so does turning it back to 0: an opaque object carries none of the transmission code. Every other drag of the four is an upload. An object carrying a shading record (geo/MaterialAttributes) takes its transmission from the record instead, per region of the field, the way its roughness does. An OPAQUE part inside a clear one shows through it, the skull inside a resin head: the refracted ray stops on it, shades it with its own colour and roughness under the scene lights and the environment, and dims it by `attenuationColor` over the stretch of medium in front of it (see geo/SDFBoolean for how the two regions are authored). That part is lit as if the medium were not around it: it casts and receives no shadow there, and the light reaching it is not tinted on its way in. A ray that cannot leave the medium (total internal reflection) turns around inside and carries on, up to `transmissionDepth` times, and `dispersion` splits the colours where it finally leaves (crossing 0 regenerates the shader once, like `transmission`). A ray that runs out of `maxStepsCount` steps inside the medium stops where it is and shows the environment straight ahead along its direction, the same as when `transmissionDepth` is spent: raise `maxStepsCount` if a long piece of glass looks clear where it should bend.