Function renderFrameSlice

src/ink/log-update.ts:1188–1494

* Render a slice of rows from the frame's screen. * Each row is rendered followed by a newline. Cursor ends at (0, endY).

(
  screen: VirtualScreen,
  frame: Frame,
  startY: number,
  endY: number,
  stylePool: StylePool,
  options?: RenderFrameSliceOptions,
)

 * Each row is rendered followed by a newline. Cursor ends at (0, endY).
 */
function renderFrameSlice(
  screen: VirtualScreen,
  frame: Frame,
  startY: number,
  endY: number,
  stylePool: StylePool,
  options?: RenderFrameSliceOptions,
): VirtualScreen {
  const renderFrameSliceStart = performance.now()
  let currentStyleId = stylePool.none
  let currentHyperlink: Hyperlink = undefined
  // Track the styleId of the last rendered cell on this line (-1 if none).
  // Passed to visibleCellAtIndex to enable fg-only space optimization.
  let lastRenderedStyleId = -1
  let lastCoveredColumn = 0

  const { width: screenWidth, cells, charPool, hyperlinkPool } = frame.screen
  let visibleCells = 0
  let skippedCells = 0
  let rowAdvanceBranchHits = 0
  let writeCellCalls = 0
  let writeCellSuccesses = 0
  let writeCellFailures = 0
  let visibleCellLookupDurationMs = 0
  let moveCursorDurationMs = 0
  let hyperlinkTransitionDurationMs = 0
  let styleTransitionDurationMs = 0
  let writeCellDurationMs = 0
  let bufferedStdoutRuns = 0
  let bufferedStdoutCells = 0
  let bufferedStdoutBytes = 0
  let bufferedGapFillCalls = 0
  let bufferedGapFillCells = 0
  const scratchCell: Cell = {
    char: ' ',
    styleId: stylePool.none,
    width: CellWidth.Narrow,
    hyperlink: undefined,
  }
  let bufferedStdout = ''
  let bufferedStdoutColumns = 0

  const flushBufferedStdout = () => {
    if (bufferedStdoutColumns === 0) {
      return
    }
    screen.diff.push({ type: 'stdout', content: bufferedStdout })
    bufferedStdoutRuns += 1
    bufferedStdoutCells += bufferedStdoutColumns
    bufferedStdoutBytes += Buffer.byteLength(bufferedStdout)
    bufferedStdout = ''
    bufferedStdoutColumns = 0
  }

  let index = startY * screenWidth
  for (let y = startY; y < endY; y += 1) {
    const rowContentEnd = frame.screen.contentEnd[y] ?? 0
    // Advance cursor to this row using LF (not CSI CUD / cursor-down).