Paragraph scroll, Clear and Fill

[ralyodio]

Three of the smaller gaps in #64, taken together because they are all about the surface a widget sits on rather than the widget.

Paragraph scroll

drawText wrapped and then drew from the first line. Long wrapped text could be displayed but not scrolled: you had to pre-slice the string, which is wrong the moment the width changes and the line count changes with it.

ui.text(prose, { wrap: true, scroll: offset });

scroll and scrollX are applied after wrapping, which is the only place either can be correct — the caller does not know how many lines their text became.

Clear and Fill

clear resets a region so an overlay can own it. modal already did this privately; without it in the open, anything else that floats is drawn into whatever it lands on and shows the widget underneath through the gaps between its words. fill floods a region with one repeated symbol.

Two details that needed deciding

A horizontal scroll can land in the middle of a double-width character. It cannot draw half of one, so what is left of that character is a space — which is what a terminal shows when a wide cell is clipped. That is dropColumns, new in every port's unicode layer, and it walks graphemes because a byte slice would cut inside one and corrupt it. Styled text needed the same thing without losing the styles of the runs that survive, so dropSpanColumns cuts inside whichever run straddles the offset and keeps its style for the remainder.

A fill with a wide symbol steps over both cells rather than writing one glyph per column: each glyph owns a continuation cell, and writing the next on top of it leaves a row of half-characters. Where the region does not divide evenly the last glyph is dropped rather than clipped, because half a wide character is not a fill, it is damage.

Scope

Six ports and seven new fixtures, all additive — nothing existing moved. This is one slice of #64; the calendar and the bounds-aware canvas are still open there, which is why this closes nothing.

Verified

• 310 TypeScript tests under both bun test and node --test, typecheck clean
• 76 widget scenes matching the reference in Rust, Go, Python, Zig and C++ (was 69)
• 11/11 ctest, every widget gallery, next build for the site

🤖 Generated with Claude Code

https://claude.ai/code/session_017Df2FNu5DhinMV2soRz3cy