Change X/Y location easier

amaximov · March 2013

Comign from Corona I was used to changing a display objects (Bitmap, Textures is that what they are called here?) locations simply by changing their ".x" and ".y" properties. Is there a way to do that with Gideros instead of "setX()". I have devised a way using EnterFrame listeners but I do not think it is very performance efficient.

ar2rsawseen · March 2013

Sorry, I did not really understand what is the problem with setters?
How this :

objet.x = 100

is much different from this:

object:setX(100)

And yes setting x property and then rechecking inside onEnterFrame and use a setter there will not be very efficient, but that how the Corona must be doing it internally.

zvardin · March 2013

http://www.giderosmobile.com/forum/discussion/comment/20571

Is a layer made by @OZApps that should accomplish that if you really want, but as there are minor syntactical differences when switching between any languages etc it may be good to learn this new way as well. I'm not sure how his tool does it, but I'm guessing you could also use metatables to perform a function when the value is read and a different function when it is set to accomplish that.

bowerandy · March 2013

@amaximov, I don't see why using setX(), setY() etc should be inefficient when used inside an ENTER_FRAME handler. After all that's the way the Gideros GTween module works and that is one of the main ways of doing tweening animations in Gideros.

best regards

amaximov · March 2013

Thanks for the replies guys! I just really liked .x and .y properties because they are faster to code

. I guess I will just use setX and setY since it may improve performance compared to Corona's implementation,

hgvyas123 · March 2013

1jetly

"new word invented can be used when any person says 110% true things"

ar2rsawseen · March 2013

@hgvyas123 where did you get it?

hgvyas123 · March 2013

@ar2rsawseen

from the movie (bollywood)

john26 · March 2013

I suspect Corona literally stores the x-component under .x and queries Lua for this every enterFrame. Gideros stores the location of everything in the C++ code which makes drawing faster. This may explain the speed differences...

One thing I'd like is the ability to access sprite children using indexing e.g.

menu:getChildAt(i):addEventListener(Event.MOUSE_DOWN,gotolevel,menu:getChildAt(i))

could be written

menu[i]:addEventListener(Event.MOUSE_DOWN,gotolevel,menu[i])

Much more readable!

atilim · March 2013

And as a side note, properties (like .x and .y) are usually implemented through __newindex meta-method and they are slow compared to :setX() and :setY().

MauMau · November 2013

+1

I found this thread because I was *exactly* looking for the same:

- Using .x / .y instead of the inconvenient :setX() / setY() methods.

- Easily accessing a sprite's children using MySprite[2] instead of MySprite:getChildAt(2)

While porting a big amount of code from Corona to Gideros, I found that using .x, .y, Sprite[n] is much cleaner, easier to maintain code. The Gideros ported code looks pretty much "spaghetti like" compared to the original.

With Corona, I used to do things like this:

MySprite[6].isVisible = showMe > 0 and true or false

It's short, easy to read any convenient. Is there any way / workaround to extend Gideros Sprite and Bitmap so we can use .x, .y, .isVisible etc. instead of the clumsy setter / getter functions?

You need those setters / getters literally hundreds of times, so shorter notations makes a big difference (and it really looks cleaner) in my own opinion.

ar2rsawseen · November 2013

Funny thing that usually Corona's code is compared as spaghetti due to the lack of OOP approach

well usually if someone asked to use MySprite[2] instead of MySprite:getChildAt(2), I'd say you are using it wrong.

But since you are in process of porting, thats completely understandable.

you can achieve MySprite[2] through __index metamethod and .x / .y through __newindex

Here are more on this topic:
http://lua-users.org/wiki/MetamethodsTutorial
http://lua-users.org/wiki/MetatableEvents

So basically you could try something like this (but be warned, that it is a slower process than setter methods):

function transform(object)
	--to get sprite[2]
	object.__oldindex = getmetatable(object).__index
 
	getmetatable(object).__index = function (t, k)
		print("test get", t, k)
		if type(k) == "number" then
			return object:getChildAt(k)
		end
		if object.__oldindex[k] then
			return object.__oldindex[k]
		end
		return nil
	end
 
	print("__newindex", getmetatable(Sprite).__newindex)
 
	getmetatable(object).__newindex = function (t, k, v)
		print("test set", t, k, v)
		if type(k) == "number" then
			return object:addChildAt(v, k)
		else
			if not pcall(object.set, object, k, v) then
				rawset(t,k,v)
			end
		end
	end
end

And use it like this:

 
transform(stage)
 
local sprite = Sprite.new()
transform(sprite)
 
stage[1] = sprite
local child = Bitmap.new(Texture.new("testbg.png"))
sprite[1] = child
 
sprite.x = 100
sprite.y = 100

amaximov · November 2013

Interesting stuff ar2rsawseen. Don't worry though I released my first Gideros game about a month ago and have come to appreciate Gideros OOP approach to Lua

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