raycast bug

duke2017 · November 2012

Found a bug in the raycast. Data is not optional. If data is missing, function arguments are shifted to the right.
but, how it works below:

function ray(data, fixture, hitX, hitY, vectX, vectY, fraction)
print("(x, y)"..hitX,hitY)
end

ray1 = stage.world:rayCast(x1, y1, x2, y2, ray, {})

and how its not work:

function ray(fixture, hitX, hitY, vectX, vectY, fraction)
print("(x, y)"..hitX,hitY)
end

ray1 = stage.world:rayCast(x1, y1, x2, y2, ray)

atilim · November 2012

Hi,

I couldn't catch the bug. On my side both

world:rayCast(x1, y1, x2, y2, function(fixture, x, y, nx, ny, fraction) end)

and

world:rayCast(x1, y1, x2, y2, function(data, fixture, x, y, nx, ny, fraction) end, data)

worked well.

Here is my full test code:

require "box2d"
 
b2.setScale(20)
 
local world = b2.World.new(0, 9.8)
 
local function createBox(x, y)
	local body = world:createBody{type = b2.DYNAMIC_BODY, position = {x = x, y = y}}
 
	local shape = b2.PolygonShape.new()
	shape:setAsBox(40, 40)
	body:createFixture{shape = shape, density = 1, restitution = 0.2, friction = 0.3}
end
 
local ground = world:createBody({})
 
local shape = b2.EdgeShape.new(-200, 400, 520, 400)
ground:createFixture({shape = shape, density = 0})
 
createBox(140, -30)
createBox(180, 300)
 
local function onEnterFrame()
	world:step(1/60, 8, 3)
 
	world:rayCast(0, 240, 320, 240, function(fixture, x, y, nx, ny, fraction)
		print(fixture, x, y, nx, ny, fraction)
	end)
 
	world:rayCast(0, 240, 320, 240, function(data, fixture, x, y, px, py, fraction)
		print(data, fixture, x, y, nx, ny, fraction)
	end, "my data")
end
 
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)
 
local debugDraw = b2.DebugDraw.new()
world:setDebugDraw(debugDraw)
stage:addChild(debugDraw)

You can look at the lines 26 and 30.

duke2017 · November 2012

no, in your code ray always passes through one object. Try this
createBox(100, -30)
createBox(190, -30)

Output:

table: 078B3D98 60 240 -1 0 0.1875

nil table: 078B2230 150 240 -1 0 (its arg+1 bug)

my data table: 078B3D98 60 240 nil nil 0.1875

my data table: 078B2230 150 240 nil nil 0.46875

atilim · November 2012

oh yes. it's a bug

now I'm fixing it. thank you.

bcos79 · February 2013

@atilim

I am trying to use rayCast with a class-based structure, and I am still seeing this bug. Here is an example setup:

main.lua

require "box2d"
test = Test.new()

test.lua

Test = Core.class(Sprite)
 
function Test:init()
	self.world = b2.World.new(0, 0)	
	self:createBox(100, 100)
 	self.world:rayCast(0, 0, 100, 100, self.rayCastCallback)
 	self.world:rayCast(0, 0, 100, 100, self.rayCastCallbackWithData, {})
end
 
function Test:createBox(x, y)
	local body = self.world:createBody{type = b2.DYNAMIC_BODY, position = {x = x, y = y}}
	local shape = b2.PolygonShape.new()
	shape:setAsBox(50, 50)
	body:createFixture{shape = shape, density = 1, restitution = 0, friction = 0}
end
 
function Test:rayCastCallback(fixture, x, y, nx, ny, fraction)
	print(fixture, x, y, nx, ny, fraction)
end
 
function Test:rayCastCallbackWithData(data, fixture, x, y, nx, ny, fraction)
	print(data, fixture, x, y, nx, ny, fraction)
end

Output

49.999998807907	49.999998807907	0	-1	0.5	nil
table: 08240FB8	49.999998807907	49.999998807907	0	-1	0.5	nil

The callback function parameter values are shifted as duke017 pointed out above and there's no fixture value.

If I remove the class-based implementation and switch everything to a simple script, it works fine. Example:

main.lua

local world = b2.World.new(0, 0)
 
local function createBox(x, y)
	local body = world:createBody{type = b2.DYNAMIC_BODY, position = {x = x, y = y}}
	local shape = b2.PolygonShape.new()
	shape:setAsBox(50, 50)
	body:createFixture{shape = shape, density = 1, restitution = 0, friction = 0}
end
 
local function rayCastCallback(fixture, x, y, nx, ny, fraction)
	print(fixture, x, y, nx, ny, fraction)
end
 
local function rayCastCallbackWithData(data, fixture, x, y, nx, ny, fraction)
	print(data, fixture, x, y, nx, ny, fraction)
end
 
createBox(100, 100)
world:rayCast(0, 0, 100, 100, rayCastCallback)
world:rayCast(0, 0, 100, 100, rayCastCallbackWithData, {})

Output

table: 082627D8	49.999998807907	49.999998807907	0	-1	0.5
table: 08240FB8	table: 082627D8	49.999998807907	49.999998807907	0	-1	0.5

In this case the callbacks works fine.

Am I missing something or is this a bug?

ar2rsawseen · February 2013

@bcos79
if you define function as method of class like this (with colon):

function Test:rayCastCallback(fixture, x, y, nx, ny, fraction)
	print(fixture, x, y, nx, ny, fraction)
end

Then as a first argument it expects the reference to the instance. That's why all arguments are shifted.

To bypassed that (like in all listeners), you would need to provide reference to instance as self when you add your listener as data parameter, like this:

self.world:rayCast(0, 0, 100, 100, self.rayCastCallback, self)
self.world:rayCast(0, 0, 100, 100, self.rayCastCallbackWithData, self)

If you need to pass additional data, make it as a property of your class, thus it will be also available in all it's methods including rayCastCallbackWithData

bcos79 · February 2013

@ar2rsawseen

Thank you for clarifying that! My apologies for thinking it was a bug.

ar2rsawseen · February 2013

It's completely ok, we are all here to learn and evolve

duke2017 · February 2013

Ohh... great((... fix one bug led to another. I upgraded from version .1 to .9, and found that rаyсast works now is not correct absolutely. not yet understand the reason, but has now changed all objects checks. its work random) earlier was checking 1,2,3,4.. objects from end. Now 2,3,1,4.. or 2,1 or depending on the position of the object.. damn.. will have to return to .1 ((

duke2017 · February 2013

nice.. I cheated myself, earler cheking is also random)) I just used the bug as a feature)
but.. but why so? why checking 1,2, and coordinate 2 is (x,y). but if coordinate 2 is (x,y+n), then checking is 2,1.. and if (x,y+m) then 1,2 again.. I'm stumped

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