Hold the phone in one hand, put the other in front of the camera, and
pinch your thumb and index finger together. A ribbon of light follows your
fingertip for as long as you hold the pinch. Let go to lift the brush.
The paint hangs on a canvas fixed a few metres out, and your fingertip
steers the brush rather than reaching to it. That is what makes it hold still: a stroke
at arm's length swings about seven degrees for every five centimetres the phone drifts
in your other hand, and the same drift is under one degree at three metres.
Steadiest of all: stand the phone up and step back. Lean it against a wall, a mug,
a book, a box — anything that holds it at roughly chest height and stops it moving.
Then both hands are free and every source of wobble goes with the camera that is no
longer moving.
For that you need Front below, because the rear camera points away from the screen:
aim the back of a propped phone at yourself and you are looking at the wall.
A newer build is ready.
Checking what this phone can do…
This one is not WebXR. Phone AR has no hand tracking — there is only a rear
camera, and ARCore does not hand joints to a web page. So this finds your hand the other
way: a hand-landmark model runs on the camera image and returns 21 points per hand,
about 25 MB of model and runtime that downloads the first time you tap Start
and is then cached. On a slow connection give it a minute.
Turning works, walking does not. The phone's gyroscope tells the page which way it
is pointing, so strokes stay put when you turn — but nothing here measures how far
you have moved. Step sideways and the drawing steps with you. Only ARCore can fix
that, and ARCore will not share the camera with this hand model, so it is one or the
other. Paint in the air is the fully world-locked one, with the phone as the brush.
Colour
Brush
Look
Anchoring to a QR code. Print any QR code as a square, put it where you want to
paint, and the drawing pins itself to that — position as well as rotation, which
a gyroscope alone can never give you. Walk around it and the drawing stays put. Come back
tomorrow, point at the same code, and what you drew is loaded exactly where you left it.
Print it big. The code has to look at least 150 px across for the anchor to
hold still — measured, not guessed. A 150 mm square is good to about three-quarters of a
metre; double the size to double the range. The panel tells you how big it currently looks.
Marker size — measure what you printed
Which camera
The rear camera and the screen point opposite ways,
so a propped-up phone aimed at you has its screen aimed at the wall. Pick
Front to prop it; pick Rear to hold it.
Camera field of view
Only matters with Hold on. Nothing reports a
phone lens's field of view, so if your strokes slide against the picture as you turn,
this is the number to change. Too narrow and they lag behind; too wide and they run ahead.