Lua Classes

[pianoman]

I tried reading the thing on inspired-lua.org, but google translate sucks, so I couldn't understand much.
Basically, what I'm asking boils down to three things: what are classes, how do you use them, and is there anything special you can do with them?
Thanks!

[Jim Bauwens]

Well, I'll try my best to explain them.

Imagine you have a game were you can have many different cars. All the cars have different things like engine power, but still share much stuff. This is were classes come in.
With classes you can make a basic structure of an object, and create new objects based on the first one. Nspire Lua has the class() function that saves us lots of work.

Example:

Code: Select All | Copy To Clipboard

1 2 3 4 5 6 7 8 9 10 11 12 13

car = class() function car: init(power, type, lights, etc)     self.power = power     self.type = type     self.lights = lights*2     self.options = etc end function car: drive(speed)    return self.power * speed -- this doesn't make much sense, but its just an example end

Now, once we made our basic car class, we can define cars using this class:

Code: Select All | Copy To Clipboard

1 2 3 4 5 6 7 8 9 10 11 12

volvo = car(10, "2x2", 4, {air-conditioning = True}) jeep = car(60, "4x4", 12, {air-conditioning = False, trailer-hook = True}) jeep:drive(10)       -- returns 600 volvo:drive(20)      -- returns 200 if jeep.options.trailer-hook then    print("The jeep can have a trailer") else    print("No trailer for you :(") end

This is just a basic example, and it written here without testing, so it can have some bugs.

[pianoman]

Oh, I think I get it. Thanks!

[pianoman]

Sorry, I'm still just a bit confused.
Let's say you created a class for a button. How would you initialize it so that you could actually draw it and do stuff with it?
Or let's say that you want to be able to create something on a keypress. How could you set it up so that, theoretically, you could continue generating objects infinitely?
I kinda tried to read the inspired-lua.org explanation, but Google Translate still sucks
Thank you very much!

[Jim Bauwens]

Well, it really depends how you want to do it

First create the class and its init script. The init script for a button would set for example it label and size. Then you need to add an paint function to it, were you draw it.
Also, you should keep a table with references to all the buttons, so that you can link event to it.
Something like this:

Code: Select All | Copy To Clipboard

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

--The table we keep all references to created buttons in ButtonTable = {} --Create the class button = class() --Create and init the button function button:init(label, x, y, action)     self.label = label     self.x = x     self.y = y     self.action = action     self.labelWidth = 0     self.width = 0     self.height = 20          table.insert(ButtonTable, self) end --Draw the button function button:paint(gc) self.labelWidth = gc:getStringWidth(self.label) self.width = self.labelWidth + 4 gc:setColorRGB(0,0,0) gc:setFont("serif", "b", 12) gc:drawRect(self.x, self.y, self.width, self.height) gc:drawString(self.label, self.x+1, self.y+2, "top") end

Well, but now you will wonder how to make it clickable and all.
Look at this full code:

Code: Select All | Copy To Clipboard

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

--The table we keep all references to created buttons in ButtonTable = {} --Create the class button = class() --Create and init the button function button:init(label, x, y, action)     self.label = label     self.x = x     self.y = y     self.action = action     self.labelWidth = 0     self.width = 0     self.height = 20          table.insert(ButtonTable, self) end --Draw the button function button:paint(gc) self.labelWidth = gc:getStringWidth(self.label) self.width = self.labelWidth + 4 gc:setColorRGB(0,0,0) gc:setFont("serif", "b", 12) gc:drawRect(self.x, self.y, self.width, self.height) gc:drawString(self.label, self.x+1, self.y+2, "top") end --What happens if you click the button function button:click() self.action() end --Check if clicked, and if clicked call its click method function button:checkClick(x, y) if y >= self.y and y <= self.y + self.height and x >= self.x and x <= self.x + self.width then self:click() end end --Check ButtonTable, and draw all the button in it function drawButtons(gc) for _, selectedButton in pairs(ButtonTable) do selectedButton:paint(gc) end end ---------------------- --The on.create even. Here we create a sample button, and make that it will call testFunction when clicked function on.create() button1 = button("Test!", 100, 50, testFunction) end --TestFunction function testFunction() bclicked = true platform.window:invalidate() end --The paint event function on.paint(gc) if bclicked then gc:drawString("The button was clicked", 10, 10, "top") end drawButtons(gc) end --Link the click event to the buttons function on.mouseDown(x, y) for _, selectedButton in pairs(ButtonTable) do selectedButton:checkClick(x, y) end end

This should explain most of it
Note that I didn't try this, so there might be some errors.

I strongly recommend you too look at the source of Adriweb's contest entry here: https://github.com/adriweb/Nspire-BreakOut .
Its a very good example of what you want to do, and should be easy to understand

EDIT:
Ok, tested it and fixed some bugs (Thanks Adriweb!)

[pianoman]

I actually understood you
Thank you once again, jim and adriweb!

[Jim Bauwens]

I'm glad I could be of help

[Levak]

Jim, we really have to translate this tutorial for inspired-lua

[Jim Bauwens]

Adriweb was planning to do it when he had some time.
I could do it, but I don't have much time either :p

[flyingfisch]

Sorry to necro-post, but cant you do this instead of using classes?

Code: Select All | Copy To Clipboard

1 2 3 4 5 6

car = {car1 = {TopSpeed=50,Weight=10},car2 = {TopSpeed=60,Weight=11}...} function PrintTopSpeed graydraw.print(car.car1.TopSpeed) end

[Nick]

euh, why would you do that? you have the ease of use to play with classes..
they're really easy to handle, what's the reason you want to do it this way?

[Jim Bauwens]

Sorry to necro-post, but cant you do this instead of using classes?

Code: Select All | Copy To Clipboard

1 2 3 4 5 6

car = {car1 = {TopSpeed=50,Weight=10},car2 = {TopSpeed=60,Weight=11}...} function PrintTopSpeed graydraw.print(car.car1.TopSpeed) end

You can, but for certain stuff classes is much better.
It allows you to do very nice stuff which are not possible (like, each car has its own subroutines).

[flyingfisch]

How do you do this with LuaForWindows? (I dont think they have a class function)

[Jim Bauwens]

No, TI added the class() function.
However, its very easy to add that function on the pc since its a simple function

[Nick]

i had some questions about that lua for windows

can you create a full program with it, with windows (real ones, not the OS) and stuff?