Four ways to ask for a thin line, drawn at true phone scale. Draw in each one.
Where this landed. None of the four shipped as drawn. Size is a hairline above the colours with its stops marked, dragged with the thumb that is already there, and the contact patch described above feeds the width underneath it.
Size is not a single number the app looks up. A stroke's radius is girth × (span + dwell) × load, and only girth is a control. The rest comes from the hand.
Four brushes, not a number.
393 pt
A painter owns a handful of brushes and knows each one by its mark. Replace the continuous size with four of them, a liner, a small round, a medium and a broad hake, each drawn as the brush it is and tapped the way the pigments are. The range each covers is still wide, because speed and contact patch still decide where inside it a stroke lands; choosing a brush sets the range, just as picking up a real brush does.
The cost: Four sizes and no more. Anyone who wants the one between two of them cannot have it, and where the four sit has to be right, because those four are all there is.
No control at all until two fingers ask for one.
393 pt
Pinch anywhere on the sheet and the brush grows or shrinks, with a ring under your fingers showing the mark it will make. Nothing is on screen the rest of the time, which matters more on a phone than it sounds, because there the paper is the whole app.
The cost: A two-finger gesture on a surface whose whole job is one-finger marks. It has to be impossible to start a stroke with it, and a pinch that goes wrong paints.
What the phone had then, made quieter.
393 pt
The vertical control on the right, but idle until touched: a faint hairline that becomes a handle under your thumb and fades again a moment later. Always in the same place, never asking for attention.
The cost: A permanent occupant of the right edge, in an app whose right edge is paper. Discoverable precisely because it is always visible, which is also the complaint.
No size control anywhere. The hand is the control.
393 pt
The contact patch is already wired in. The native touch module reports the ellipse your finger makes and a tracker calibrates its range to your hand. Lean in and the mark widens; come up onto the tip and it narrows. Nothing on screen at all.
The cost: The sensor is the limit. majorRadius is quantised and its usable band is narrow, so the tracker has to fit a rolling range to each hand and never has more than about a threefold span to work with. That is a brush, not a brush set.
| Screen it costs | Sizes reachable | Found without being told | |
|---|---|---|---|
| 筆 Brush rack | a row, ~150pt wide | 4 | yes, it looks like the palette |
| 摘 Pinch | none | continuous | maybe, since pinch is a habit |
| 縁 Edge slider | right edge, always | continuous | yes |
| 圧 Press | none | ~3× span, per hand | no |
筆 and 摘 together is the pairing I would build. The rack gives four brushes you can name and reach for, which is how this medium actually works and costs one legible row; pinch gives the size between two of them for anyone who wants it, and costs nothing until used. Neither leaves anything sitting on the paper.
圧 alone cannot carry it. The contact patch is real and already feeding the width, but its usable span is about threefold after calibration. That is one brush's worth of range, not a set of brushes. It belongs underneath whichever control is chosen, which is where it already is.