Author Topic: Add function to the gc class (Read 26760 times)

Frog · « **on:** September 02, 2011, 11:25:19 am »

Hi everyone! I've been following this forum for quite some time now, but never actually posted something. I guess this is the first time: I've got a question...

I'm trying to add methods and properties to the default gc class. I know that in "normal" lua you can just do something like this: function table.method(). So I tried the following:

Code: [Select]

function gc:method(x, y, width, height)
	self:drawRect(x, y, width, height)
end

This didn't work though. I also tried to create a new class called screen that inherits from gc, but that didn't work either. Finally I tried "screen = gc:begin()", but that was no solution as well.

So my question is: how can I add my own method to the default gc class? Thanks!

Loulou 54 · « **Reply #1 on:** September 02, 2011, 11:42:03 am »

I've seen 3 solutions :
* You can put gc as an argument :

Code: [Select]

function on.paint(gc)
method(gc)
end

function method(gc)
[...]
end

* You can also use platform.gc() instead of gc. For example : platform.gc():drawString(...
But I've had some problem with this method.. Some functions as setFont if I remember don't work well..

* Or you can copy gc in a global variable at the beginning of the on.paint function.

Code: [Select]

function on.paint(gc)
gc2=gc
end

function method()
gc2:drawString(...
end

Adriweb do this in the last version of better Lua.

Frog · « **Reply #2 on:** September 02, 2011, 11:46:35 am »

Thanks for your answer! That's not exactly what I mean though. I'm trying to add a new method to the gc, so that I can (for example) call gc:drawButton(). In other languages I would extend/subclass the gc class, but I'm not sure how to do that in TI-Lua. At first I thought I should do newGC = class(gc), but that didn't work, just like defining the function: function gc:drawButton(). How can I do this?

Scipi · « **Reply #3 on:** September 02, 2011, 11:54:26 am »

I think you could achieve the same effect by doing as Loulou showed, where you basically create a whole separate function that uses the gc variable. Such as:

Code: [Select]

function on.paint(gc)
    method(gc) --is called in on.paint and is passed the gc var
end

function method(gc)
    gc:drawRect(...) --note the gc:
end

you could perhaps try calling the function

Code: [Select]

gc:method(gc) --pass the gc variable
    --Do stuff here

Though I don't know if that would work.

Frog · « **Reply #4 on:** September 02, 2011, 12:00:09 pm »

I know a separate function is possible, but I think it's way cleaner to make it part of the actual gc, so that the drawButton() method sits prettily next to the drawRect() method. It sounds way more logical to me.

The latter is exactly what I'm trying to achieve, but that's unfortunately not possible using your code...

Jim Bauwens · « **Reply #5 on:** September 02, 2011, 12:21:00 pm »

Code: (Lua) [Select]

gc = getmetatable(platform.gc())

function gc:test()
	self:setColorRGB(0,0,0)
	self:fillRect(10,10,10,10)
end


function on.paint(gc)
	gc:test()
end

That should do the trick

Adriweb · « **Reply #6 on:** September 02, 2011, 12:26:06 pm »

Good ideas in this topic !

However, I should point out that using platform.gc() is discouraged, and is generally a bad idea.
(multiple reasons like the fact that it's not working the exact same way as the 'normal' gc, and for future compatibility matters...

)

Frog · « **Reply #7 on:** September 02, 2011, 12:30:06 pm »

Thanks a lot, that's works like a charm! I need to improve my understanding of metatables though...

3rik · « **Reply #8 on:** September 02, 2011, 12:55:29 pm »

Would this work?

Code: [Select]

function on.paint(gc)
	gc2 = getmetatable(gc)
	function gc2:method(x, y, height, width)
		self:setColorRGB(0,0,0)
		self:fillRect(x, y, height, width)
	end
--more methods to define here
	function on.paint(gc) --Your normal on.paint(gc) goes in here
		gc:method(10,10,10,10)
	end
end

It would use the normal gc to define all the methods the first time on.paint is called then when it is done it would redefine itself.

Frog · « **Reply #9 on:** September 02, 2011, 12:56:55 pm »

Quote from: adriweb on September 02, 2011, 12:26:06 pm

Good ideas in this topic !

However, I should point out that using platform.gc() is discouraged, and is generally a bad idea.
(multiple reasons like the fact that it's not working the exact same way as the 'normal' gc, and for future compatibility matters... )

Somehow I overlooked your post... Anyways, isn't it true that the usage of platform.gc() in jimbauwens' example is no bad practice, since getmetatables is just a reference to the original metatable shared by all gc objects? I mean, you do use the passed gc in the on.paint() function, so that shouldn't give unexpected results?

Don't you agree that this way looks like a better method for a GUI library?

Levak · « **Reply #10 on:** September 02, 2011, 01:12:10 pm »

Quote from: Frog on September 02, 2011, 12:56:55 pm

Quote from: adriweb on September 02, 2011, 12:26:06 pm
Good ideas in this topic !

However, I should point out that using platform.gc() is discouraged, and is generally a bad idea.
(multiple reasons like the fact that it's not working the exact same way as the 'normal' gc, and for future compatibility matters... )

Somehow I overlooked your post... Anyways, isn't it true that the usage of platform.gc() in jimbauwens' example is no bad practice, since getmetatables is just a reference to the original metatable shared by all gc objects? I mean, you do use the passed gc in the on.paint() function, so that shouldn't give unexpected results?

Don't you agree that this way looks like a better method for a GUI library?

platform.gc() is a constructor of a new independant gc object.

What does the TINspire framework do :

Code: [Select]

local gc=platform.gc()
gc:begin()
on.paint(gc)
gc:finish()

What does that mean ? On each screen refresh, it recreate an independant gc object that has a different reference.

And since it is a different object, using methods such as setFont/setColor won't change gc, but your new object you define each time you use platform.gc.

If you want to store this gc in on.paint(), it won't be drawn as it, since it has a different reference/address

In Jim method, you define, yes, one time a new object, but you pick up its meta table. It is not the same. Each gc object has the same metatable, but not the same properties.

Quote from: 3rik on September 02, 2011, 12:55:29 pm

Would this work?

It would use the normal gc to define all the methods the first time on.paint is called then when it is done it would redefine itself.

Ouch :p
Just use a boolean, like if not gc2 then ..... end in your on.paint()

but anyway, look at the fisrt part of my post, you can't do so :p

Frog · « **Reply #11 on:** September 02, 2011, 01:15:28 pm »

Quote from: Levak on September 02, 2011, 01:12:10 pm

Quote from: Frog on September 02, 2011, 12:56:55 pm
Quote from: adriweb on September 02, 2011, 12:26:06 pm
Good ideas in this topic !

However, I should point out that using platform.gc() is discouraged, and is generally a bad idea.
(multiple reasons like the fact that it's not working the exact same way as the 'normal' gc, and for future compatibility matters... )

Somehow I overlooked your post... Anyways, isn't it true that the usage of platform.gc() in jimbauwens' example is no bad practice, since getmetatables is just a reference to the original metatable shared by all gc objects? I mean, you do use the passed gc in the on.paint() function, so that shouldn't give unexpected results?

Don't you agree that this way looks like a better method for a GUI library?

platform.gc() is a constructor of a new independant gc object.

What does the TINspire framework is :

Code: [Select]
local gc=platform.gc() gc:begin() on.paint(gc) gc:finish()
What does that mean ? On each screen refresh, it recreate an independant gc object that has a different reference.

And since it is a different object, using methods such as setFont/setColor won't change gc, but your new object you define each time you use platform.gc.

If you want to store this gc in on.paint(), it won't be drawn as it, since it has a different reference/address

In Jim method, you define, yes, one time a new object, but you pick up its meta table. It is not the same. Each gc object has the same metatable, but not the same properties.

Yes, I understand. The metatable is basically the blueprint and obviously every instance has different properties. I'm using to Jim's method to create a simple graphics library now. Should I release the code when I'm finished?

Jim Bauwens · « **Reply #12 on:** September 02, 2011, 01:32:12 pm »

I'm glad I could be of help

You don't need to release your source, but it would be nice

Frog · « **Reply #13 on:** September 02, 2011, 01:41:58 pm »

If I think it's worth it, I'll release it.

Now that I'm busy I've actually got one more question...

Can you get the currently set color property from the gc? I've tried showing the table on the screen to show all properties, but that didn't work. Maybe someone knows what property the set RGB color is stored in, so I can calculate the opposite color for my fillButton function?

Jim Bauwens · « **Reply #14 on:** September 02, 2011, 01:44:22 pm »

I don't think that that is possible.
What I would do is create a new gc:setColorRGB (with another name) and store the current color information to a table.
However, the color can be changed when you draw an image, so you need to watch out with that.

Author Topic: Add function to the gc class (Read 26760 times)

Frog

Add function to the gc class

Loulou 54

Re: Add function to the gc class

Frog

Re: Add function to the gc class

Scipi

Re: Add function to the gc class

Frog

Re: Add function to the gc class

Jim Bauwens

Re: Add function to the gc class

Adriweb

Re: Add function to the gc class

Frog

Re: Add function to the gc class

3rik

Re: Add function to the gc class

Frog

Re: Add function to the gc class

Levak

Re: Add function to the gc class

Frog

Re: Add function to the gc class

Jim Bauwens

Re: Add function to the gc class

Frog

Re: Add function to the gc class

Jim Bauwens

Re: Add function to the gc class