Drawing an icon

Action icons

On the pixel grid

Every horizontal and vertical edge lies on a whole pixel. So does every point where a curve runs exactly horizontal or vertical: the top of a circle, the outer edge of a ring, the end of a rounded cap. A circle is centred so that its radius lands on whole pixels, and a 1px ring runs between two whole-pixel radii around the same centre.

A diagonal can only meet the grid at its ends, so its ends and the corners it forms are held to the rule instead. Geometry taken from another icon is checked again rather than trusted: a borrowed shape brings its drift with it.

Corners

Convex corners are rounded by 0.5px, as on the bars of the plus or the frame of the desktop device. Acute corners such as arrowheads, tip included, take 0.25px. Concave corners stay sharp, and so do the ends of 1px lines. Larger frames that belong to a family keep that family's radius: the window icons use 1px.

Rounding a corner that is not a right angle moves its outermost point off the grid. The corner is then shifted until the curve's extreme lands on a whole pixel, rather than keeping the vertex on the grid and letting the curve drift.

Overlay icons

Drawn at 11x11px. An overlay sits in the corner of another icon rather than standing on its own, so it is the one part of the set not drawn to the 16 pixel grid.

Which grid an icon is on

Counted from the set as it stands, not stated once and left to rot. A drawing that does not sit on one of these is drawn to a box nothing else in the set uses.