graphics objects flickering when attached to body?

Redpicman

Hi all,

when I create a circle physics object and by using applyForce() move it from the bottom to the top of the screen. The physics object moves smoothly as expected. When I attach a graphic to it, it also moves smoothly up the screen. The problem is however, the graphic flickers, and therefore looks faint. I guess this is happening for three reasons: 1) the physics object is moving about 5 pixels a step, and the graphic has to redraw itself evertime. 2) both the body and the graphic is quite small (maybe 5 to 6 pixels diameter). I have tried the graphic as a stand alone graphic and as part of a sprite sheet but I cant see no difference. 3)I have the step rate at 60 frames a second.

Are there any strategies to get the graphic to move without flickering. Another thing to note that this thing is created at runtime (it is a bullet) where as the other object that is created at the start of the level does not flcker when moved (but there again it moves slower and is bigger. I am moving the graphic to the body by using the object:setPosition() function. Is the optimum way of doing this?

I am sure there is an optimum way of doing this, so if anyone has ideas, I am all ears (and eyes).

antix

In your EnterFrame code, are you getting the position of the physics body and setting the sprites position accordingly? Something like this..

local body = physicsObject.body   graphicObject:setRotation( body:getAngle() * (180 / math.pi) ) graphicObject:setPosition( body:getPosition() )

totebo

Also, make sure you update the Sprite and Box2D in the same loop. If you use two separate loops, you sometimes get strange behaviour in my experience.

Redpicman

Hi antix and totebo,

Yes I think I am doing both of those things. Here is a cutdown version of the code that I am using (note I am using Scenemanager for level control)

----- level one set up--
Level1 = Core.class(Sprite)
function Level1:init()

function self:fireBullet()
local x,y = self.playerTank.tankBody:getPosition()
self.bullet = Bullet.new(self,x,y)
self:addChild(self.bullet)
end



function self:onEnterFrame()

self.world:step(1/60, 8,3)
self.playerTank:moveTank()
self.playerTank:upDateImage()
if(self.bullet) then
self.bullet:updateImage()
end

end

self:addEventListener(Event.ENTER_FRAME, self.onEnterFrame,self)

--- Bullet Class -------

Bullet = Core.class(Sprite)

function Bullet:init(lvl , objectX, objectY)
print(objectX, objectY)

local x,y = self.body:getPosition()
self.body:applyForce(0,-5,x,y)

self.bulletImg = Bitmap.new(Texture.new("images/bullet.png"))
self.bulletImg:setAnchorPoint(0.5,0.5)
self.bulletImg:setPosition(objectX, objectY - 20)
self:addChild(self.bulletImg)

self.xOffset , self.yOffset = self.bulletImg:getPosition()

local circle = b2.CircleShape.new( objectX, objectY - 20, 2)
self.body = lvl.world:createBody({type = b2.DYNAMIC_BODY})
self.body:createFixture({shape = circle, density = 1.0, friction = 1.0, restitution = 0.2})



function self:updateImage()
--print("click")
local Xbod,Ybod = self.body:getPosition()
self.bulletImg:setPosition(Xbod + self.xOffset, Ybod + self.yOffset)

end


end

end