overriding class methods?

jack0088 · August 2012

How to override class methods? Is it possible to extend a method or redefine it completely? How about constructors - say I would want to extend the Sprite.init?

ar2rsawseen · August 2012

Gideros class system is very felxible.

You can both overwrite/redefine methods or extend any existing class

Here's example of overriding Bitmap class to save reference to the texture it was created with

--save new method as some other method
Bitmap.__new = Bitmap.new
 
--redefine new method
function Bitmap.new(texture)
	--create real Bitmap instance
	self = Bitmap.__new(texture)
	--save texture as property
	self.texture = texture
	return instance
	return self
end
 
--additional method to return texture
function Bitmap:getTexture()
	return self.texture
end

And here's of extending Bitmap class with new constructor:

--extend new class from Bitmap
newBitmap = Core.class(Bitmap)
 
--define new constructor (should accept atleast same arguments)
function newBitmap:init(texture)
	--Bitmap constructor is automatically called here
	--so this class will have all standard methods and properties
	--of parent class
	--we only need to add new ones
	self.texture = texture
end
 
--and define method to return texture
function newBitmap:getTexture()
	return self.texture
end

Hope that helps

jack0088 · August 2012

ähm, yes, I was looking for something like the first example.. but I can't get it to work.
What's wrong here?

do
	local spriteInit = Sprite.new --cache
 
	function Sprite.new()
		local instance = spriteInit() --call default class behavior
		instance.coordinate = {       --extend class by a table
			x = 0,
			y = 0
		}
		return instance
	end
end

Sprite.coordinate doesn't exist after calling Sprite.new()

EDIT:
Also tried this way, which I think is the same:

Sprite.__new = Sprite.new
 
function Sprite.new()
	self = Sprite.__new()
	self.coordinate = {
		x = 0,
		y = 0
	}
	return self
end

ar2rsawseen · August 2012

It works for me:

do
	local spriteInit = Sprite.new --cache
 
	function Sprite.new()
		local instance = spriteInit() --call default class behavior
		instance.coordinate = {       --extend class by a table
			x = 0,
			y = 0
		}
		return instance
	end
end
 
local sprite = Sprite.new()
print(sprite.coordinate.x)
print(sprite.coordinate.y)

If you want Sprite class and not instance) to have coordinates, then it's easy, you could have done it simply:

Sprite.coordinate = {       --extend class by a table
			x = 0,
			y = 0
		}

jack0088 · August 2012

But then Sprite doesn't propagate this value to it's instances.. at least I thought so?!

PS: If I extend the Sprite class with this table, WHY the Shape class doesn't has it too, when a call Shape.new()?

ar2rsawseen · August 2012

But then Sprite doesn't propagate this value to it's instances.. at least I thought so?!

What do you mean?

PS: If I extend the Sprite class with this table, WHY the Shape class doesn't has it too, when a call Shape.new()?

Because Shape class extends Sprite class somewhere internally, much before you modify Sprite class

jack0088 · August 2012

Because Shape class extends Sprite class somewhere internally, much before you modify Sprite class

I'm still a stupid noob to Gideros, maybe because I aint work regularly with the SDK.
The whole FAQ was due to my anchorPoint dilemma some time before, where I asked you about manipulating the getPosition() output.
I wanted to rewrite/modify the Sprite class and have the anchorPoints working for all the classes inherited from the Sprite (e.g. Shape). BUT as you pointed out - I have a problem now. To get it work with Sprite, Shape, etc. I have to do it for every class separately, am I right?

Ufff... maybe I should forget about development. Maybe I'm just not the right guy for this stuff.

ar2rsawseen · August 2012

No, don't get frustrated. Everyone makes the mistakes while in learning phase.

So what do you do, if you are not a developer?

But to answer your question, yes basically, you'll need to implement setAnchorPoint for every class you want to have it. And it's quite easy to do that.

You can create simple function (I can't remember implementation of anchor point from the top of my head so I'll use what you had):

function implementAnchorpoint(anyClass)
	local newInit = anyClass.new --cache
 
	function anyClass.new()
		local instance = newInit() --call default class behavior
		instance.coordinate = {       --extend class by a table
			x = 0,
			y = 0
		}
		return instance
	end
end
 
--apply to all needed classes
implementAnchorpoint(Sprite)
implementAnchorpoint(Shape)
--etc

jack0088 · August 2012

oh my god.. the solution is elegant and seems now to be so obvious... thank you @ar2rsawseen for being here! Ok. I try my best.

PS: I'm actually designer. But a few years ago I did some web development in php, mysql, html, css and all that stuff. Then I dropped because of the army.. now I'm trying to find my niche.

ar2rsawseen · August 2012

Considering the fact that you find the solution elegant means you have a good taste in coding.
Meaning you'll be fine, just keep learning

jack0088 · August 2012

I written it down, and I think it should work correctly but somehow it doesn't. Why?
Here is my class for AnchorPoints functionality.

local function AnchorPoint( Class )
 
	Class.__new = Class.new --cache
 
	function Class.new()
 
		local instance = Class.__new() --call default class behavior
 
 
		--add AnchorPoint methods...
 
		instance.anchorPoint = {
			x = 0,
			y = 0,
			offsetX = 0,
			offsetY = 0,
		}
 
 
		instance.__setX = Class.setX
		instance.__setY = Class.setY
		instance.__getX = Class.getX
		instance.__getY = Class.getY
 
 
		function instance:getOffsetX()
			return self:getWidth()  * self.anchorPoint.x
		end
 
		function instance:getOffsetY()
			return self:getHeight() * self.anchorPoint.y
		end
 
 
		function instance:setAnchorPoint( cx, cy )
			self.anchorPoint.x, self.anchorPoint.y = cx, cy
			self:setPosition( self.__getX(self), self.__getY(self) ) --refresh
		end
 
		function instance:getAnchorPoint()
			return self.anchorPoint.x, self.anchorPoint.y
		end
 
 
		function instance:setX( x )
			self.anchorPoint.offsetX = self:getOffsetX()
			self.__setX( self, x - self.anchorPoint.offsetX )
		end
 
		function instance:setY( y )
			self.anchorPoint.offsetY = self:getOffsetY()
			self.__setY( self, y - self.anchorPoint.offsetY )
		end
 
 
		function instance:getX()
			local x = self.__getX(self) + self.anchorPoint.offsetX
			self.anchorPoint.offsetX = 0
			return x
		end
 
		function instance:getY()
			local y = self.__getY(self) + self.anchorPoint.offsetY
			self.anchorPoint.offsetY = 0
			return y
		end
 
 
		function instance:setPosition( x, y )
			self:setX(x)
			self:setY(y)
		end
 
		function instance:getPosition()
			print("#", self:getX(), self:getY()) --returns (0,0)!
			return self:getX(), self:getY()
		end
 
 
		return instance
 
	end
 
end
 
 
--apply to classes
AnchorPoint( Sprite )
AnchorPoint( Shape  )

If I create a Shape and call :getPosition() I somehow reach the original behavior not my modified class function.

local rect = Primitive.new() --equivalent to Shape.new()
rect:newRect(0,0, 101,101) --method of Primitive; 101x101px at screen origin
rect:setAnchorPoint(.5, 0)
print("R",rect:getPosition()) --returns (-59,0)???

My function should have nulled it out by "+self.anchorPoint.offsetX"...

ar2rsawseen · August 2012

Well hard to tell without deeper debugging. (BTW you can debug by putting print function inside new added/overwritten methods, to see if everything happens how it's expected.)

Will try to check it deeper, but first comment would be, try not to use reserved variables. As variable Class is a global variable for extendind/creating new classes

jack0088 · August 2012

I tried to cache the original functions locally for example like:

local __setX = Class.setX
local __setY = Class.setY
local __getX = Class.getX
local __getY = Class.getY

But same result. Also I used your suggested method of debugging at the instance:getPosition() method above.

print("#", self:getX(), self:getY()) --returns (0,0)!

This print() gives me the correct value of (0,0), but inside the main.lua it returns a different value of (-59,0)

print("R",rect:getPosition()) --returns (-59,0)???

If you'll have some time to check this, maybe you can get it to work in a better manner?

ar2rsawseen · August 2012

Ok I think I've figured it out.

First thing I noticed, that this value changes. If you comment out print function inside instance:getPosition()

And instead you'll call print("R",rect:getPosition()) --returns (-59,0)??? like you did in the in the end of the code it returns 0,0 coordinate.

Now try calling print("R",rect:getPosition()) two times. First one will return 0,0 and second one will return -59,0

It is because inside getX and getY methods you reset self.anchorPoint.offsetX = 0
So next time you call it anchorPoint is zero again

jack0088 · August 2012

double post

jack0088 · August 2012

I think I got it to work. Thank you again many times! The only think I have to add is setRotation. And test Sprite inheritance..

jack0088 · August 2012

Waaahh.. I'm going crazy! @ar2rsawseen I've modified the class and it seems working now, but I can't get the :setRotation method to work! Could you be so good and help me out again? PLEASE!
I've prepared the project for you:

jack0088 · August 2012

I figured out where the issue lies... After the Object was rotated, the rotation point is shifted a little, because the overall shape changed (width, height). So anyone any idea how to get this shifted length?

ar2rsawseen · August 2012

Working on it

ar2rsawseen · August 2012

Well mathematical solution to this problem:

local dx = self:getAnchorPointOffsetX()
local dy = self:getAnchorPointOffsetY()
local cosine = math.cos(math.rad(n))
local sine = math.sin(math.rad(n))
local newX = dx - (dx*cosine - dy*sine)
local newY = dy - (dy*cosine + dx*sine)
self:setPosition(self:getX() + newX, self:getY() + newY)

But is does not work as I expected.
It still misses about 10px for 15deg and 20px for 30deg on both axis.
Don't know where they come form, or what I'm not taking into consideration.

Getting too late here, maybe I should leave it to other evening

ar2rsawseen · August 2012

Ok got it with the help of my wife.

You don't need to reset anchor point to 0 to rotate and then put it back. It can stay in same anchor, somehow I missed that.

So here's a working project:
http://appcodingeasy.com/anchorPointFixed.zip

Now it's definitely good night for me

Edited:
Don't know why I couldn't upload the file to forum. It always ended up as 0byte file

jack0088 · August 2012

haha:)))) you and your wife are geniuses!

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