Unexpected behaviour in events and objects

[cristoferfb]

Hi, I implemented my object with the classic module: https://github.com/rxi/classic/blob/master/classic.lua

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Node = Object.extend(Object)

function Node:new (imgDir)
	self.img = love.graphics.newImage(imgDir)
end

function Node:draw (y, scale)
	-- This if works for know if a node is in the middle of the screen.
	if (y + self.img:getHeight()/2)*scale < (love.graphics.getHeight()/2 + self.img:getHeight()*scale/2) and (yPosition + self.img:getHeight()/2)*scale > (love.graphics.getHeight() / 2 - self.img:getHeight()*scale / 2) then
		love.graphics.setColor(102/255, 138/255, 1)
		love.event.push('fixPosition', love.graphics.getHeight()/2 - (y + self.img:getHeight()/2)*scale)
		love.event.push('setFocusNode', self)
	end

	centerX = love.graphics.getWidth() / 2 - self.img:getWidth() * scale / 2
        love.graphics.draw(self.img, centerX, y * scale, 0, scale, scale)
        love.graphics.setColor(1, 1, 1)
end

function Node:trigger () 
	test = 0
end

The only relevant part of the code above is the next:

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love.event.push('setFocusNode', self)

then in the event handler:

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function love.handlers.setFocusNode (node)
	node:trigger()
end

result in the next error:

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Error

main.lua:52: attempt to call method 'trigger' (a nil value)


Traceback

main.lua:52: in function <main.lua:51>
[C]: in function 'xpcall'

What do u think about that? I tried a lot of differents way for get it work.

pd: node:draw() is call in the function love.draw ().

[grump]

What you receive in the event handler is a copy of the table that has the original metatable stripped from it.

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function love.handlers.foo(t)
	print("received", t, getmetatable(t))
end

local t = setmetatable({}, {})
print("sending", t, getmetatable(t))
love.event.push("foo", t)

Output:

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sending	table: 0x418b3a00	table: 0x418b3a28
received	table: 0x403c6450	nil

[cristoferfb]

What you receive in the event handler is a copy of the table that has the original metatable stripped from it.

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function love.handlers.foo(t)
	print("received", t, getmetatable(t))
end

local t = setmetatable({}, {})
print("sending", t, getmetatable(t))
love.event.push("foo", t)

Output:

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sending	table: 0x418b3a00	table: 0x418b3a28
received	table: 0x403c6450	nil

Yeah, apparently I am trying to do the things in the C (pointers) style. I did a little more research on how lua works internally and i think I need to rethink my implementation.

[pgimeno]

I believe this quirk happens because the events can be sent by a thread, therefore its contents need to be independent of the Lua context (because different threads use different Lua contexts in Löve), therefore the values need to be copied, not referenced. The metatable is not copied, but even if it was, since the target object is a copy and not the original object, the method could possibly be modifying the wrong object.

[cristoferfb]

I believe this quirk happens because the events can be sent by a thread, therefore its contents need to be independent of the Lua context (because different threads use different Lua contexts in Löve), therefore the values need to be copied, not referenced. The metatable is not copied, but even if it was, since the target object is a copy and not the original object, the method could possibly be modifying the wrong object.

Yes, every node check if himself is in the center of the screen, finally I externalized the logic for get it work.