restoreCursor not working when current line is at bottom of terminal?

I am trying to use a singleColumnMenu to display some options. The idea here is when the user selects an item, the app will:

1. Clear the singleColumnMenu
2. Replace it with a .inputField
3. Gather the input
4. Redisplay the singleColumnMenu where it was before

I tried some preliminary code to see if I could accomplish steps 1-2, but restoreCursor() is acting in a nondeterministic fashion. I’m on OSX in Terminal.app.

If I cmd-K my terminal to clear the screen, my app works perfectly. In fact I can execute the app a few times and it still works perfectly. However, when my terminal’s prompt get down near the bottom of my terminal screen and I execute my program, the menu is not erased and the input is placed after the menu items. If I cmd-K and run again, everything works fine again.

I’ve attached a gif that shows what’s happening.

Here is the code:

var term = require( 'terminal-kit' ).terminal ;

var items = [
  'Option 1.' ,
  'Option 2.' ,
  'Option 3.'
] ;

term.saveCursor();
start();

function start() {
  //display the menu
  term.singleColumnMenu( items , ( error , response ) => {
    //restore the cursor to where it was before the menu was displayed
    term.restoreCursor();
    //console.log(`origX=${origX}, origY=${origY}`);
    //term.moveTo(origX, origY);
    term.eraseDisplayBelow();
    //dsiplay the input field where the menu once was
    term(' Enter some text: ');
    term
      .inputField(function( error, input ) {
        term.restoreCursor();
        term.eraseDisplayBelow();
        term.singleColumnMenu( items, (error, response) => { process.exit(); } );
      });
  } ) ;
}

[cronvel]

@ctataryn Hi, .saveCursor()/.restoreCursor() are deterministic, however you are suggesting it works on a coordinate system based upon the text flow, while in reality it works with the terminal coordinate system.

Let me explain what happened:

• the cursor is at the bottom of the screen, you save its position
• some text forces a scrolling of the terminal’s content
• you restore the saved cursor position, but it has scrolled and the cursor doesn’t care about it: it is indeed restored at the bottom of the screen

But you want to move the cursor at the beginning of the single column menu. Sadly there is no easy way to do it, since terminals don’t track scrolling. They do not emit some magical terminal scrolling event that Terminal-kit would receive, so you are basically on your own because you alone know what your app is doing.

There are a lot of workaround for that, for example:

• Workaround 1: don’t use .saveCursor()/.restoreCursor(), instead move the cursor up using the appropriate number of line (since you know how many options had been sent to .singleColumnMenu().
• Workaround 2: before using .saveCursor()/.restoreCursor(), output some \n then call term.up(n) with n matching the number of newline characters: this way you prepare an area big enough to receive your .singleColumnMenu()

[ctataryn]

Fair enough, I’ll change my approach back to the original way. Again, thank you for your attentive help.

---

From: Cedric Ronvel [e-mail] Sent: Friday, November 17, 2017 7:36:28 AM To: cronvel/terminal-kit Cc: Craig Tataryn; Mention Subject: Re: [cronvel/terminal-kit] restoreCursor not working when current line is at bottom of terminal? (#59)

@ctatarynhttps://github.com/ctataryn Maybe it’s not well documented here, but when using continueOnSubmit, most keys stop doing anything unless the user cancel its choice with the backspace or delete key (key bindings are configurable).

To be honest, the menu was coded with one menu call per user input in mind.

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