Function effectiveStyleAt

internal/app/render.go:328–359

effectiveStyleAt returns the SGR sequence active at visual column `col` within string `s` — i.e., the last CSI seen before that column. An empty return means no style was active (terminal default).

(s string, col int)

// within string `s` — i.e., the last CSI seen before that column. An
// empty return means no style was active (terminal default).
func effectiveStyleAt(s string, col int) string {
	last := ""
	visible := 0
	i := 0
	for i < len(s) {
		if s[i] == '\x1b' && i+1 < len(s) {
			j := i + 2
			for j < len(s) {
				ch := s[j]
				if (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') {
					j++
					break
				}
				j++
			}
			last = s[i:j]
			i = j
			continue
		}
		if visible >= col {
			break
		}
		_, size := utf8Decode(s[i:])
		if size == 0 {
			i++
			continue
		}
		i += size
		visible++
	}
	return last
}

// SpliceOverlay splices `overlay` onto `bg` at visual cell position
// (x, y). Both strings are newline-separated; ANSI CSI escapes are