in src/lib/CodeMirror/indentationMarkers.ts [15:33]
export function getVisibleLines(view: EditorView, state = view.state): Set<Line> {
const lines = new Set<Line>();
for (const { from, to } of view.visibleRanges) {
let pos = from;
while (pos <= to) {
const line = state.doc.lineAt(pos);
if (!lines.has(line)) {
lines.add(line);
}
pos = line.to + 1;
}
}
return lines;
}