Raycast

duke2017 · August 2012

Is there any examples of using a raycast? How return parameter of "the fixture hit by the ray"?

wall( 100, 100, 50, 50 )
function rayfunc(event)
???
end
ray = self.world:rayCast(0, 0, 200, 200, rayfunc)

jack0088 · August 2012

changing the Alpha?

duke2017 · August 2012

Alpha?) No.. I'm talking about b2.World:rayCast(x1, y1, x2, y2, listener, data)
I need to know which object was crossing ray. how this parameter is considered?
sorry for my english)

ar2rsawseen · August 2012

the parameter listener is the callback function which accepts 6 or 7 parameters.
First one is the fixture hit by the ray

duke2017 · August 2012

yes, I understand that, but how exactly do I callback this the first parameter?

function rayfunc(event)
if event."First parameter" == box then
......
elseif."First parameter" == crate then
....
end
end
ray = self.world:rayCast(0, 0, 200, 200, rayfunc)

I do not understand how to read its "first parameter"..

ar2rsawseen · August 2012

Ok.

So, for example, you have a variable world where you have world instance and some kind of box2d object ball. You want to project raycast on x axis through all the screen and get fixture if there is one

local x, y = ball:getPosition()
local screenWidth = application:getContentWidth()
 
local raycastCallback function(fixture, hitX, hitY, vectX, vectY, fration)
    --so if this function is called, it means we hit some kind of object
    --and it's fixture is stored in first variable we named "fixture"
    --so we can for example get body
    local body = fixture:getBody()
 
end
 
--now we add callback function for projected raycast
--Parameters:
--object x coordinate
--object y coordinate
--projection vector on x axis
--projection vector on y axis
--callback function
world:rayCast(x, y, x+screenWidth, y, raycastCallback)

duke2017 · August 2012

Oh, sorry for my stupidity)) Thank you very much for the detailed explanation! What would I do without you)

ar2rsawseen · August 2012

@duke2017 thats completely ok, we're all there to learn

jdbc · October 2013

I am trying to use world:rayCasting and after I called to rayCastCallback function, but it seems fixtures are not sorted.

I mean I defined the function:

list = {}

function raycastCallback (fixture, hitX, hitY, vectX, vectY, fration)
local body = fixture:getBody()
list[#list + 1] = body
end

but list is not sorted in the sense of the raycast. Is it correct?

ar2rsawseen · November 2013

@jdbc it should return the first fixture it hits by the ray cast, and then depending on your return value

return no value or -1: ignore this fixture and continue
return 0: terminate the ray cast
return fraction: clip the ray to this point
return 1: don't clip the ray and continue

either proceed to next fixture or terminate, etc

jdbc · November 2013

I use rayCastCallback function to check collision between a fixed body and a set of bodies on the left, returning 1.

A list of collision points is built but this list is not ordered by axis X (sense of raycast from fixed body to the left side), it seems to be randomized.

Anyway I can ordered this list by axis X but I believe raycast will do it the job.

ar2rsawseen · November 2013

Well it should be ordered by the increasing distance from your starting point to the raycasting direction, which might not always be increasing with the x axis values (depending on your direction).

if its not, maybe there is some other problem

jdbc · November 2013

I execute something like:

local left = -2000

-- Left hits
self.world:rayCast( v:getX(), v:getY(), v:getX() + left, v:getY(), self.raycastCallback, self)

where v is a sprite object and self.list is the bodies list and contains all bodies in the raycast trajectory but sometimes not ordered.

I suppose it is a behaviour of box2d engine.

Howdy, Stranger!

Categories

In this Discussion

Top Posters

Raycast

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

Raycast

Comments