# tvision-m2 - a TVision/Turbo-Vision style toolkit in GNU Modula-2

A character-cell UI toolkit written in ISO GNU Modula-2 (`gm2 -fiso`) that
runs in a terminal (xterm and friends).  It is a small, self-contained
Turbo-Vision-like library: a retained view tree with clipping and z-order,
a diffed ANSI cell screen, keyboard and mouse decoding (xterm SGR mouse
reports), widgets, and modal dialogs.

Everything is Modula-2 except `tvtty.def`, the tiny libc binding used to put
the terminal in raw mode and to query its size (`termios`, `ioctl`, `read`,
`write`).  There is no C source and no graphics dependency.

## Files

| file | role |
|---|---|
| `tvtty.def` | libc binding (raw mode, winsize, read/write) |
| `tv.def` / `tv.mod` | the toolkit: screen, view tree, widgets, events |
| `demo.mod` | demo application |
| `ttysize.mod` | diagnostic: checks the tty binding |

## Build & run

    gm2 -fiso -c tvtty.def
    gm2 -fiso -I. -c tv.mod
    gm2 -fiso -I. tv.o demo.mod -o demo
    ./demo

or simply `make`.  Run it from a real terminal; `Esc` exits.

## What works

- Alternate screen, hidden/show cursor, terminal restored on exit.
- 16-colour foreground/background with blink; UTF-8 output (box-drawing).
- Perspective view tree: groups and windows contain children; drawing is
  clipped to each window; overlapping windows are ordered (z-order) and the
  one you click comes to the front.
- Windows: double-line frame, title, ` X ` close box, draggable by the title
  bar with the mouse.
- Menu bar + drop-down menus (mouse and keyboard).
- Widgets: static text, single/double frame, input line (insert, backspace,
  delete, Home/End/arrows), push button, check box, radio buttons, list box
  with selection and wheel scrolling, vertical scroll bar.
- Focus chain: `Tab`/`Shift-Tab` and up/down cycle widgets; the focused
  input gets the hardware cursor.
- Keyboard decoding: printable UTF-8, arrows, Home/End, PgUp/PgDn, Ins/Del,
  Tab/Shift-Tab, F1-F12, Enter, Space, Backspace, Esc, Ctrl-C.
- Mouse: xterm SGR reporting - click to focus/press, drag window titles,
  click list rows, wheel-scroll lists.
- Diffed redraw (only changed cells are written).
- Modal dialog helper (`Message`), used by the demo's OK button.
- Menu bar with drop-down menus: click a title (or press `F10`), navigate
  with Left/Right/Up/Down, select with Enter/Space or a mouse click;
  item separators (`MenuSep`) are supported.  The selected item's tag is
  returned by `HandleEvent`.

## Roadmap ideas

- Modal `Dialog` with arbitrary controls; form validation.
- Menu item hotkeys (Alt+letter) and check/radio menu items.
- Nested clipping groups and a desktop with many windows / tiling.
- More widgets: multi-line editor, tabs, combo box, progress bar.
- `SIGWINCH`-driven relayout (today the app polls the size).
- Mouse hover highlight and resizable windows.

## GNU Modula-2 notes

- Value-returning procedures with no parameters need explicit `()`
  (`PROCEDURE Cols() : INTEGER;`), otherwise the `.def` fails to parse when
  compiled through the `.mod`.
- Pointer fields require `^` (`v^.rect`); there is no implicit dereference.
- A compound `BEGIN ... END` block is not a statement, so it cannot appear
  directly in a `CASE` alternative - use a helper procedure.
- An `INTEGER` index compared with `HIGH(array)` (a `CARDINAL`) must be
  converted: `i <= VAL(INTEGER, HIGH(a))`.
- The libc `struct termios`/`struct winsize` are accessed through an opaque
  byte buffer with fixed Linux offsets (see `tv.mod`).