lab_glass

Laboratory glass for Mother Liquor — borosilicate, amber reagent glass, a fume hood sash, a wired door pane and the liquid standing in a burette, all off one surface shader.

It reads the scene already drawn behind the fragment through zero::scene_color and displaces that read by the surface's own tilt in clip space, so a piece of this glass bends the room standing behind it. That matters here because the film has no sky and no outdoors: the builtin PBR transmission refracts the environment probe, and an interior that has killed its skybox has nothing in one. Three reads a hair apart give a thick edge its colour fringe.

Beer–Lambert absorption runs over the path the wall makes at the current angle, so wall_thickness and absorb_color turn one shader into a 2 mm borosilicate that barely tints and a 3 mm amber Winchester that goes brown. The white line every real piece of glassware carries — the rim, the ground lip, the moulded graduation — comes from edge_color against the grazing angle, and the specular comes from the room's own practicals through zero_pbr_shade over a black albedo.

Coverage, and why a material on this shader composites premultiplied

One scene-colour copy serves the whole transparent pass, so every blended surface in a frame reads the same picture: the lit opaque scene as it stood before any of them drew. A piece of glass returning alpha = 1 therefore paints that picture over every other piece already drawn behind it — a rack forty pieces deep shows only its front pane, and the pane erases the rack.

So this shader states how much of the background it actually disturbs. coverage is that fraction looked at straight on — near 0.1 across a clean flat pane, near 0.9 through an amber vessel wall — and it rises to 1 at a grazing angle either way. The fragment returns its contribution already multiplied by it, and the material asks for blend: premultiplied (src + dst * (1 - src.a)), so what is left of the background is whatever was drawn there, glass included. Layers then stack: the sash keeps its highlight, the flask behind it keeps its bend, and neither erases the other.

A material on this shader that asks for alphaBlend instead will hide everything behind it. cull: none and depth_write: false are the other two render-block values a vessel wants, so both walls draw and overlapping pieces both survive.

Properties

tint · roughness · ior — the glass itself. refract_strength · dispersion — how far the bend drags the frame, and how far apart the three colour reads sit. absorb_color · absorb_distance · wall_thickness — the absorption integral. edge_color · edge_power · edge_gain — the white rim. spec_gain · opacity · coverage — the highlight, the overall presence, and the compositing fraction above.