Refresh the screen

In startUp(), replace the commented placeholder in the event loop:

    while (e.should_quit == false) {

        // refresh the screen

        try e.refreshScreen();

We'll do the drawing with this function, that goes in a new section, which I put above the Helpers section:

///////////////////////////////////////////////////////////////////////////////
//
//                              Screen update
//
///////////////////////////////////////////////////////////////////////////////

/// Full refresh of the screen.
fn refreshScreen(e: *Editor) !void {
    // code to come...
}

We'll have to explain what goes on.

• we clear our ArrayList, which will eventually contain the characters that must be printed

• we set the background color, hide the terminal cursor so that it doesn't get in the way, and move the cursor to the top left position

• we draw the rows, later we'll also draw the statusline and the message area

    e.surface.clearRetainingCapacity();

    try e.toSurface(ansi.BgDefault);
    try e.toSurface(ansi.HideCursor);
    try e.toSurface(ansi.CursorTopLeft);

    try e.drawRows();
    // try e.drawStatusline();
    // try e.drawMessageBar();

• we move the cursor to its current position and we show it again

• we print the whole thing with a write() call

    const V = &e.view;

    // move cursor to its current position (could have been moved with keys)
    var buf: [32]u8 = undefined;
    const row = V.cy - V.rowoff + 1;
    const col = V.rx - V.coloff + 1;
    try e.toSurface(try ansi.moveCursorTo(&buf, row, col));
    try e.toSurface(ansi.ShowCursor);

    try linux.write(e.surface.items);

moveCursorTo()

To move the cursor we'll need a new function in ansi.zig:

/// Return the escape sequence to move the cursor to a position.
pub fn moveCursorTo(buf: []u8, row: usize, col: usize) ![]const u8 {
    return std.fmt.bufPrint(buf, CSI ++ "{};{}H", .{ row, col });
}

It takes a slice buf and formats it to generate an escape sequence that will move the cursor to a position.