Function drainAdaptive

src/ink/render-node-to-output.ts:124–157

(
  node: DOMElement,
  pending: number,
  innerHeight: number,
)

// xterm.js adaptive drain. Returns rows applied; mutates pendingScrollDelta.
function drainAdaptive(
  node: DOMElement,
  pending: number,
  innerHeight: number,
): number {
  const sign = pending > 0 ? 1 : -1
  let abs = Math.abs(pending)
  let applied = 0
  // Snap excess beyond animation window so big flicks don't coast.
  if (abs > SCROLL_MAX_PENDING) {
    applied += sign * (abs - SCROLL_MAX_PENDING)
    abs = SCROLL_MAX_PENDING
  }
  // ≤5: drain all (slow click = instant). Above: small fixed step.
  const step =
    abs <= SCROLL_INSTANT_THRESHOLD
      ? abs
      : abs < SCROLL_HIGH_PENDING
        ? SCROLL_STEP_MED
        : SCROLL_STEP_HIGH
  applied += sign * step
  const rem = abs - step
  // Cap total at innerHeight-1 so DECSTBM blit+shift fast path fires
  // (matches drainProportional). Excess stays in pendingScrollDelta.
  const cap = Math.max(1, innerHeight - 1)
  const totalAbs = Math.abs(applied)
  if (totalAbs > cap) {
    const excess = totalAbs - cap
    node.pendingScrollDelta = sign * (rem + excess)
    return sign * cap
  }
  node.pendingScrollDelta = rem > 0 ? sign * rem : undefined
  return applied
}

// Native proportional drain. step = max(MIN, floor(abs*3/4)), capped at
// innerHeight-1 so DECSTBM + blit+shift fast path fire.