overriding class methods?

jack0088

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

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

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

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

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

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

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

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

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

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

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

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

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

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

double post

jack0088

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

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

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

Working on it

ar2rsawseen

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

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

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