Functional reactive programming and LuaGravity

Magnusviri · March 2012

@ techdojo mentioned component game design in this thread

http://www.giderosmobile.com/forum/discussion/comment/3846#Comment_3846

And it has pretty well sucked me in and I've eventually landed on LauGravity.

http://www.lua.inf.puc-rio.br/~francisco/luagravity/

Has anyone used it?

Magnusviri · March 2012

Ok, so LuaGravity seems to be more of a concept than something that is actually used.

Anyway, I liked some of the ideas and they can sort of be implemented with coroutines anyway, so I rewrote the HelloBall example using coroutines. It's about 5 lines shorter and much more interesting to read in my opinion. The if's are gone and replaced with whiles. I could have left in the local x and y variables but decided it was safer to do it this way (if there were other ways of setting the ball position).

The original HelloBall is here:

http://www.giderosmobile.com/documentation/getting_started.html

 
local background = Bitmap.new(Texture.new("field.png"))
stage:addChild(background)
 
local fruit = Bitmap.new(Texture.new("ball.png"))
 
fruit.xspeed = 1.5
fruit.yspeed = 2.3
 
stage:addChild(fruit)
 
function moveBallX()
	while true do
		while fruit:getX() < 320 -fruit:getWidth() do
			fruit:setX( fruit:getX() + fruit.xspeed )
			coroutine.yield()
		end
		while fruit:getX() > 0 do
			fruit:setX( fruit:getX() - fruit.xspeed )
			coroutine.yield()
		end
	end
end
 
function moveBallY()
	while true do
		while fruit:getY() < 480 -fruit:getHeight() do
			fruit:setY( fruit:getY() + fruit.yspeed )
			coroutine.yield()
		end
		while fruit:getY() > 0 do
			fruit:setY( fruit:getY() - fruit.yspeed )
			coroutine.yield()
		end
	end
end
 
co_moveBallX = coroutine.create(moveBallX)
co_moveBallY = coroutine.create(moveBallY)
 
function onEnterFrame(event)
	coroutine.resume(co_moveBallX)
	coroutine.resume(co_moveBallY)
end
 
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)

ndoss · March 2012

Ooh, neat! I read about lua gravity after reading your first post which then led me to coroutines which then led me nowhere .... I couldn't exactly see how to use them in Gideros.

This example helps greatly! Thanks!

Magnusviri · March 2012

Oh I'm wrong, it's 6 lines longer. And I think how I'm controlling one variable is kind of inefficient. But I can see this working to control an AI or game timeline really well.

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