[ii-impy]

Adds watering_can, a new shader player Setup (ADR-0021). Closes #163.

What visitors see

• Empty room: plain paper with a muted crayon sun in the top-right corner.
• Standing in one spot: sprouts start at the lowest points of the silhouette (feet, hands, the bottom of a raised arm) and climb. They become dense leafy vines, and over about 20 s they bloom into a mixed bouquet. The person is never drawn: you only see them through what grows on them. Colour ripens with growth, from muted to vivid, so full bloom is the payoff.
• Waggling is free: the plants ride on the body. Arm waves, flailing, swaying and bending don't cost any growth.
• Walking rewinds: if the feet move to a new spot, in any direction (including toward or away from the camera), the growth plays backwards. Once the person stops, it resumes from where the rewind left off.
• The sun follows the garden: it brightens and grows rays as total growth rises.

How it works

• Buffer B, body memory (per pixel):
  • Presence: soft, hole-filled and eased.
  • Run extents: the bottom and top of the vertical stretch of body each pixel sits in. They are measured on a screen-fixed grid, so a run's rows agree on its ends.
  • Owner slot.
  • A "hold": a lost person's plants fade over 2 s instead of popping, and every texel of a person steps together.
• Buffer C, garden state:
  • Per tracked person: growth, the planted spot, and the base (feet), measured locally.
  • Walking detection.
  • A ghost per slot, so someone who briefly drops out of tracking or gets a new ID keeps their growth.
  • Inheritance on tracker splits.
  • The sun level.
  • A coarse "body nearby" grid, so an empty paper pixel costs one fetch.
• Image: paper, then the crayon sun, then vines, leaves and flowers derived from B and C every frame.
• Tunables: all of them are at the top of common.glsl. Edit and press R.
• Design and plan: the design is docs/superpowers/specs/2026-11-06-watering-can-design.md, with the approved mockup next to it. The build plan is in docs/superpowers/plans/.

Testing

• test_watering_can.py adds 53 headless GL tests, driven by the real BodyBlobs tracker on synthetic masks with a 10 fps camera under a 30 fps render. They cover:
  • full bloom in about 20 s under edge flicker and dropout holes
  • arm waving and weight shifts not rewinding
  • sideways and toward/away steps rewinding
  • growth resuming after a walk
  • neighbours staying independent
  • two touching still people whose contact flickers both keep growing
  • tracker loss, re-ID, merge/split and split-off limbs keeping growth
  • fades that don't pop or tear
  • thin arms blooming
  • the frame being stable under flicker
  • timing independent of render rate (1/30 to 1/240)
  • bounded state
• make test: 452 passed.
• I checked stills of each growth stage by eye. --mock-camera --windowed ran at 30 fps (the frame cap) on a desktop GPU.

Known issue (not fixed in this PR)

• Two people walking together whose contact flickers faster than every 0.5 s keep growing instead of rewinding.
  • Cause: the re-plant that protects touching still people from merge/split flicker also suppresses step detection.
  • Suggested fix: keep counting a step whenever the locally measured base moves past WALK_DIST from the spot, even while re-planting.
  • Smaller related cases: a re-planting neighbour can mask a merged coasting track's walking, and someone arriving close to a walker suppresses that walker's steps for 0.5 s.

Not verified yet

• Frame rate on the show Pi 5. Check this before the show. The Setup is in setups.json. Per pixel, a body pixel costs about 29–47 B taps; C costs about 590k fetches a frame. If it's short, cut in this order: leaf count, petal count, VINE_NEIGHBOURS, RUN_STEPS.
• The real Orbbec camera. None of the following has been checked with it: the walking threshold (WALK_DIST), feet window (BASE_WIN), flicker immunity or re-ID inheritance. On site with --camera:
  • stand 25 s: you should reach full bloom with no rewind
  • wave your arms: nothing should rewind
  • take one sideways step: it should visibly rewind
  • two people stand touching for 25 s: both should keep growing
• Jumping in place: it may count as walking. Tune on site.
• Mouse check and Shadertoy paste: the --test-input mouse check and pasting the tabs into Shadertoy haven't been done.

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