How a polygon's pixels get their colours.

• {:flat, colour} — one colour
• {:texture, texture, light} — a Cauldron3D.Texture repeated across the polygon by its uvs, through the light table at light (0 to 255, 128 the texture's own colours), or as it is when light is nil
• {:shaded, texture} — as :texture, the light carried across from the polygon's lights
• {:surface, texture} — a texture already lit, its edge pixels repeated beyond it
• {:warp, texture, opts} — a texture rippling as liquid does: each place on it moved by :amplitude pixels (default 8.0) along a sine of the other axis, of :wavelength pixels (default 128.0), moving with :time seconds at :speed (default 1.0) turns a second; :light as :texture's, default nil
• {:sky, layers, opts} — a sky at no distance: layers is a list of {texture, speed}, nearest first, each drawn where the one before is colour :clear (default 0) and moving speed pixels a second with :time; :scale (default 378.0) is how far across the sky a view straight ahead reaches, and :flatten (default 3.0) squashes it toward the horizon
• {:fun, fun} — fun.(first, stop, y, setup, context) returns the stop - first colours of the run itself

The context is a map: :light_table (rows of 256 colours, brightest first), :light_rows (how many rows it has), :background (the colour behind every polygon), and :view, which {:sky, ...} reads. Light value v uses row (255 - v) * light_rows / 256, held inside the table.