Detecting "touch" on box2d body

arjunr24724

I have been trying to use the queryAABB method to create a fixture on the touch/mouse coordinate to detect which body (randomly spawning, active and moving, 32x32) has been touched.

local function onTouchesBegin(event)
local x = event.touch.x
local y = event.touch.y
local fixtures = thisLevel.B2_Worlds[1]:queryAABB(x - 0.00005, y - 0.00005, x + 0.00005, y + 0.00005)
if #fixtures > 0 then
local body = fixtures[1]:getBody()
print("Begins: Touched something!")
end
end

However, this doesn't seem to yield consistent results. Sometimes I get #fixtures>0, most times I don't. Changing queryAABB size doesn't really affect the outcome. I want to avoid Sprite hit-detection.

Any ideas?

arjunr24724

nvm

for those who need to know, don't forget to use stage:globalToLocal(x,y) on the returned event's coordinates.

atilim

This simple code works fine. I hope it helps understanding what's wrong on your side:

require "box2d"   local world = b2.World.new(0, 0)   local function createBox(x, y, w, h, name) local shape = b2.PolygonShape.new() shape:setAsBox(w, h)   local body = world:createBody{type = b2.STATIC_BODY, position = {x = x, y = y}} body:createFixture{shape = shape}   body.name = name   return body end   for i=1,20 do createBox(math.random(0, 320), math.random(0, 480), 30, 20, "box "..i) end   local function onTouchesBegin(event) local x = event.touch.x local y = event.touch.y local fixtures = world:queryAABB(x - 0.00005, y - 0.00005, x + 0.00005, y + 0.00005) if #fixtures > 0 then local body = fixtures[1]:getBody() print("touched "..body.name) end end   stage:addEventListener(Event.TOUCHES_BEGIN, onTouchesBegin)   local debugDraw = b2.DebugDraw.new() world:setDebugDraw(debugDraw) stage:addChild(debugDraw)

arjunr24724

Thanks. I used pretty much the same code. Except, I had to use stage:globalToLocal(event.x, event.y) when onTouchesBegin() was called to get the correct coordinates. Other than that, queryAABB worked exactly as it should.

I am using TiledAsWorldEditor class to manage the world. Maybe thats why.