[sidorares]

Found running @react-x11/components' browser example on Windows for the first time. react-x11 asked the bridge for things it did not have, and a page differed from Chrome's in ways a reader sees at once. Each item here is one of those.

Cursor

setCursor(windowId, name) maps a CSS cursor name to a system cursor: the link hand, the I-beam, the resize arrows, wait, not-allowed. none hides the cursor. The window answers WM_SETCURSOR over its client area with the cursor last set. Where the pointer is already over the window, the new cursor shows at once, since the move that changed what's under it was answered before the name arrived.

react-x11 already calls native.setCursor?.(id, name) for every window and for every <Frame> pane's host, but the class cursor was IDC_ARROW and nothing answered. No link ever showed the hand on Windows. I checked this with the real pointer: hand over a link, I-beam over text, crosshair where a page sets one, arrow elsewhere, both in a window and through a <Frame> pane.

Text

• fontFamilyOf(name) looks up a name the system collection has no family for, the way GDI does (CreateFontFromLOGFONT). It answers { family, weight, stretch, italic }. DirectWrite groups faces by weight, width and slope, so Arial Black, Arial Narrow, Segoe UI Light and Franklin Gothic Medium are faces of other families, and fontExists says no to each. Chrome finds them all, and a page naming one fell back to the default face.
• Font width (stretch, 1–9): on layoutCreate's options and spans, and as the fifth argument of fontMetrics and fontHandle. This is what reaches a narrow face. It's part of the handle cache key.
• letterSpacing on a span, through IDWriteTextLayout1::SetCharacterSpacing. Without it, CSS letter-spacing came out tight, and react-x11's <Html>, which justifies through letter spacing when the engine can't justify itself, left every justified paragraph ragged.
• features on a span, { smcp: 1, liga: 0 } by tag, through an IDWriteTypography.
• xHeight and capHeight from fontMetrics: what CSS's ex and cap units are measured in.

Tests

test/text.js covers the GDI lookup (Segoe UI Semibold → Segoe UI 600, an unknown name → null), the width on handles and spans, letter spacing (five characters at 2 px each come out 10 px wider), features, and the new metrics. npm run test:unit and npm run test:window pass locally on Windows 11.

The react-x11 half is in the core PR that follows this one. It feature-detects fontFamilyOf and is harmless against 0.0.7.

Still open (not in this PR)

Under a lineHeight, layoutCreate uses proportional spacing with the baseline at 0.8 × multiple. At a multiple of 1 that puts the baseline at 80% of the face's. react-x11 now reads the ascent and descent the bridge measures, so <Html> compensates, but core's own <text> still draws high in its line box under a line height. That's for a follow-up.

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