# "Ice" means slick, not frozen water

**"Ice" / "icy" is the dev name for a surface type, not a material.** In these files, in the map
names (icyjumps), in `geometry.json` (`"material": "ice"`), in the grey box shots (light blue) and in
the [creative direction questionnaire](creative-direction.md) (questions 23 and 33), "ice" means
one thing only: **a slick surface**, a floor you slide on.

## What it is in the game

In the map a slick surface is a shader flag (`surfaceparm slick`, `SURF_SLICK` in the BSP). The
physics is Urban Terror's, exactly:

- **no friction:** you keep your speed and glide, you can't stop or turn sharply by running;
- **sprinting is 4× stronger** than in the air, but only gains while you turn (arcs);
- it can be a floor, a ramp, a curved wall or a glass tube; anywhere the flag is set.

That is all the game knows. It does not know whether the surface is cold, white or wet.

## What it can look like

Anything a player can believably **skate on**. Frozen water is one option among many:

| looks like | fits |
|---|---|
| ice: clear, frosted, cracked, glacier blue | frozen worlds, the original icyjumps feel |
| polished steel, chrome, brushed metal sheets | factories, stations, labs |
| wet glass, glazed ceramic, black mirror floors | luxury sci-fi, clean architecture |
| oiled or lacquered floors, rubber tracks | industrial, sports arenas |
| glowing glass, energy floors, light bridges | abstract, futuristic, alien |
| maglev rails, magnetic plates | conduits, tubes, transport systems |
| smooth stone, marble, obsidian | temples, ancient structures |

A concept can pick one look for the whole map, or let it change by place (an ice canyon outside, a
steel conduit inside), as long as each place is consistent.

## The skates (a later idea)

The runner could wear boots that **deploy skates automatically** on slick surfaces:

- normal ground: blades folded in, running stride, footsteps;
- touching a slick surface: the blades (or wheels, or mag pads) snap out with a click, the legs
  switch to skating strokes, the sound becomes a carve;
- leaving it: they fold back.

The kind of skate can follow the surface: blades on ice, inline wheels on polished metal, magnetic
pads on rails, glowing runners on energy floors. **This is only visual and sound.** The physics
stays UrT's slick, the same on every look; the animation follows the movement, never the other way
round. (The same idea is described for the frozen city in the Airtime repo's
`docs/world/concept-design.md`, "Blades on ice".)

## Rules for designers

1. **Slick must always read as slick.** Whatever the material, the player has to see at a glance
   where they will slide and where they can stand: gloss, reflections, a consistent colour or pattern.
   Beauty must never hide it.
2. **One language per place.** Within an area, every slick surface uses the same look, and no
   non-slick surface uses it.
3. **Non-slick surfaces look rough:** concrete, grip plates, rubber, snow (snow is grippy, not
   slick), grating.
4. **The flag decides, not the look.** Which surfaces are slick comes from the map
   (`geometry.json`: `"material": "ice"`, or the `slick` flag on faces and patches), never from a
   concept image. A concept may change how a slick surface looks, never which surfaces are slick.
5. **Slick glass is still slick.** Some icyjumps floors and tubes are see-through *and* slick; they
   are `"material": "ice"` with `"see_through": true`. Show both: a transparent surface that still
   reads as one you slide on.