Lua Q&A

[pianoman]

Hi everyone! I couldn't find a good place to post various questions, so I thought I'd start this.

First of all, how do you use the timer and make it do something? All I can do is start it.

Thank you!

[Ashbad]

You can start the timer with Timer.start(period), which sets a period of time in seconds for the timer to start.  You can then set up an on.timer() event that is activated every timer tick. You can stop it with timer.stop().

[Jim Bauwens]

Here is a little example:

Code: (Lua) [Select]


number = 0

function on.paint(gc)

    --If number is still zero (we just started the application), start the timer (set to tick every 1 seconds)
    if number==0 then
        timer.start(1)
    end

    --Draw the number on the screen
    gc:drawString(tonumber(number),10, 10, "top")
end


--This get's now called every 1 seconds until you stop the timer
function on.timer()
    --Add one to number
    number = number + 1

    --Force the screen to be redrawn
    platform.window:invalidate()

    --If number is 10, stop the timer
    if number==10 then
        timer.stop()
    end
end



[pianoman]

Oh, got it. Thanks!

[pianoman]

Another one:
are you able to change values of an array in the program?
Thanks!

[Jim Bauwens]

Well, technically speaking its tables in Lua

Lets say you have this table:

Code: (Lua) [Select]

a={1,2,3,4,5}Then you can change the third item with this command:

Code: (Lua) [Select]

a[3] = 1337Your table will then look like this:

Code: (Lua) [Select]

{1,2,1337,4,5}

[pianoman]

Omigod that just made a game a million times easier.
Thanks!

[pianoman]

How about this one: are you able to check if two tables are equal to each other?
for example:

Code: [Select]

a={1,2,3}
b={1,2,4}

function on.paint(gc)
if a==b then
gc:drawString("E",0,0,"top")
else
gc:drawString("I",0,0,"top")
end


[Jim Bauwens]

Sadly enough you can't just compare a table like that (unless you add a metatable for it with the appropriate funcion).
You can do it like this:

Code: (Lua) [Select]


function compare(t1, t2)
    for i, p in pairs(t1) do
        if p~=t2[i] then
            return false
        end
    end
    return true
end

a={1,2,3}
b={1,2,3}

if compare(a, b) then
--they are equal
else
--they are not equal
end


[pianoman]

What's "p" in that code?
And what does "in pairs" mean?

[Jim Bauwens]

Its a way to loop through all the items of an Array.

Example: (works only on computer, as it uses print)

Code: (Lua) [Select]

    mytable={1,2,3,"a","b","c"}

    for i, p in pairs(mytable) do
       print("Spot: " . i)
       print("Content: " . p)
    end
will output

Code: (Lua) [Select]

Spot: 1
Content: 1
Spot: 2
Content: 2
Spot: 3
Content: 3
Spot: 4
Content: a
Spot: 5
Content: b
Spot: 6
Content: c

i is the spot in the table, p is the content of that spot.

Here is some handy information about tables: http://lua-users.org/wiki/TablesTutorial

[pianoman]

Oh, I get it. Thanks, jimbauwens!

[Jim Bauwens]

No problem

[pianoman]

Sorry, but I have another one:
is there a randint feature in lua?

EDIT: Never mind, I figured it out.

[pianoman]

Is there a way to display what the user is typing (i.e. a text box)?
I have a feeling it uses getText, but I don't know how to use it, and the TI manual is really confusing.