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Josh

Coroutine Example

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I wanted to better understand coroutines so I wrote this example. I discovered that Lua errors in coroutine functions do not get caught by the debugger for some reason. The program will just silently close with no error message.

I am interested in somehow creating a stack of coroutines. Like this:

self:AddCoroutine(MoveToPoint,10,0,0))
self:AddCoroutine(TurnToRotation,0,90,0))
self:AddCoroutine(MoveToPoint,10,0,5))
self:AddCoroutine(ChangeColor,1,0,0,1))
self:AddCoroutine(ChangeColor,1,1,1,1))

When one coroutine is completed, the next one on the stack would begin. So if you called the above code just once, it would cause the object to move to (10,0,0), then slowly rotate it by 90 degrees, then move it again, then fade the color to red, then fade back to white.

Any ideas on this? I feel like it would be very powerful for games but it's hard to think about abstractly.

function MoveToPoint(entity, targetpos, speed)
	
	while true do
		coroutine.yield()

		local currentpos = entity:GetPosition()
		local change = targetpos - currentpos
		local dist = change:Length()
		
		if dist <= speed then
			
			--We have reached our target
			entity:SetPosition(targetpos)
			break
			
		end
		
		--Keep moving towards the target
		currentpos = currentpos + change / dist * speed
		entity:SetPosition(currentpos)
		
	end
end

window = Window:Create("",0,0,1280,720)
context=Context:Create(window,0)
world=World:Create()

local pivot = Pivot:Create()
local dest = Vec3(10,0,0)

--Create the coroutine
co = coroutine.create(MoveToPoint)

--Send coroutine parameters in the first call
--The coroutine yields right away so it won't do anything else yet
coroutine.resume(co, pivot, dest, 0.5)

while coroutine.status(co) ~= "dead" do
	System:Print(pivot.position)
	coroutine.resume(co)
end

 

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"The program will just silently close with no error message."

 

Look at the definition of coroutine.resume() because it returns 2 values and 1 of them is if there is an error. I noticed the debugger doesn't show these so if there is an error I write it out to console so at least I can see the error.

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