Key handling and rawset

[BillC]

I was experimenting with key handling (see http://www.shatters.net/forum/viewtopic.php?f=6&t=12653&st=0&sk=t&sd=a&start=45#p109115) and I wanted to post something over here on this forum.

Following Chris's example (http://www.shatters.net/forum/viewtopic.php?f=9&t=9813&start=0&st=0&sk=t&sd=a&hilit=key+handler), let's say you have a collection of key assignments contained in a table called "keyhandlers":

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keyhandlers =
{
  G = fast_goto,
  ["1"] = toggle_ecliptic_grid,
  etc,
  etc
}


and a function that handles the key input:

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function handlekey(k)
  handler = keyhandlers[k.char]
  if (handler ~= nil) then
    handler()
    return true
  else
    return false
  end
end


and a command that ties the "key" event to the "handlekey" function:

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celestia:registereventhandler("key", handlekey)


Now if you've already run this script (in start.celx, say), is there a way to add another key assignment to the table, or add another table to the function, by running another script?

Adding another key assignment is pretty simple - just run a script with this command:

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rawset(keyhandlers, "A", toggle_plates)


(Of course, if "A" was assigned to a different function originally, this command will reassign it.)

You can also have the script look for the existence of the "keyhandlers" table, and if it doesn't find it, create it:

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if (keyhandlers == nil) then
  keyhandlers = { ["A"] = toggle_plates }
  celestia:registereventhandler("key", handlekey)
else
  rawset(keyhandlers, "A", toggle_plates)
end


But to make it work, you will have to add the "handlekey" function to the script as well:

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function handlekey(k)
  handler = keyhandlers[k.char]
  if (handler ~= nil) then
    handler()
    return true
  else
    return false
  end
end


This will overwrite any previous declaration of "handlekey", which won't be a problem if it's identical.

Now let's say your script creates a new table called "keyhandlers2". Can you include this table in the "handlekey" function along with the original key handling table?

Use this variation of the key handling function:

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function handlekey(k)
  handler = keyhandlers[k.char]
  handler2 = keyhandlers2[k.char]
  if (handler ~= nil) then
    handler()
    return true
  elseif (handler2 ~= nil) then
    handler2()
   return true
  else
    return false
  end
end


When you run your script, the old function "handlekey" will be overwritten with this version, but the original "keyhandlers" table will still work.

[Vincent]

Now if you've already run this script (in start.celx, say), is there a way to add another key assignment to the table, or add another table to the function, by running another script?

Bill,

You should be able to do this by adding this single line:

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keyhandlers["A"] = toggle_plates

[BillC]

Thanks Vincent!

Ha ha, I missed the obvious!

I've also used this format:

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keyhandlers = { ["A"] = toggle_plates }

But I think yours is more elegant.

[Vincent]

Thanks Vincent!

You're welcome, Bob.

I've also used this format:

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keyhandlers = { ["A"] = toggle_plates }

But I think yours is more elegant.

It's not only a question of elegance. The problem with your code is that it defines
a fresh new keyhandlers table, and thus, it deletes the previous keys assignments.
Whereas my code simply adds the new key assignment on top of the existing ones.

[BobHegwood]

You're welcome, Bob.

Methinks you meant to say "Bill."

[Vincent]

You're welcome, Bob.

Methinks you meant to say "Bill."

Oops, sorry Bill.
And thanks... Bob!