# `Tela.Renderer`
[🔗](https://github.com/idabmat/tela/blob/v0.1.0/lib/tela/renderer.ex#L1)

Produces minimal ANSI output to update the terminal from one frame to the next.

The renderer compares the previous frame's lines against the next frame's lines
and emits ANSI escape sequences only for lines that have changed. This avoids
full-screen redraws on every update, preventing flicker.

## Usage

    prev = ["Hello", "World"]
    next = ["Hello", "Tela"]

    iodata = Tela.Renderer.diff(prev, next)
    :io.put_chars(:user, iodata)

On the first render, pass an empty list as `prev` to clear the screen and
write all lines.

    iodata = Tela.Renderer.diff([], ["Hello", "Tela"])

## Cursor parking

After every render the cursor is moved to the row immediately below the last
line of the frame. This keeps the cursor out of the visible UI area.

## ANSI sequences used

| Sequence | Meaning |
|---|---|
| `\e[2J` | Clear entire screen |
| `\e[H` | Move cursor to top-left (home) |
| `\e[R;CH` | Move cursor to row R, column C |
| `\e[K` | Clear from cursor to end of line |

# `diff`

```elixir
@spec diff(prev_lines :: [String.t()], next_lines :: [String.t()]) :: iodata()
```

Produces iodata to update the terminal from `prev_lines` to `next_lines`.

Compares each line by index. For lines that differ, emits a cursor-move
sequence followed by the new content and an end-of-line clear. Lines that
are identical produce no output.

When `prev_lines` is empty, performs a full clear (`\e[2J\e[H`) before
writing all lines.

After writing, the cursor is parked one row below the last line.

## Examples

    iex> Tela.Renderer.diff([], ["Hello"]) |> IO.iodata_to_binary()
    "\e[2J\e[H\e[1;1HHello\e[K\e[2;1H"

    iex> Tela.Renderer.diff(["Hello"], ["Hello"]) |> IO.iodata_to_binary()
    ""

---

*Consult [api-reference.md](api-reference.md) for complete listing*