Simple Circle Class

Cesar · May 2016

I just want to share a simple Circle class

Circle = Core.class(Shape)
 
function Circle:init(x, y, radius)
	local sides=math.floor(radius/2)
	local angleStep=360/sides
	--self:setFillStyle(Shape.SOLID, 0xff0000, 1)
	self:setLineStyle(1, 0xff0000, 0.8)
	self:beginPath()
	self:moveTo(radius, 0)
 
	for i = 1,sides do
		local angle = math.rad(i*angleStep)
		xx = math.cos(angle)*radius	
		yy = math.sin(angle)*radius	
		self:lineTo(xx,yy)	
	end
 
	self:endPath()
	self:setPosition(x,y)	
end

antix · May 2016

@Cesar, thanks for sharing

Here's a function to test if a given x,y position is inside a circle..

function Circle:pointInCircle(x, y)
  local r = self.radius ^ 2
  if (y - self.y) ^ 2 / r + (x - self.x) ^ 2 / r <= 1 then return true end
  return false
end

Also, if you ever want to expand the abilities of your circle class to include collision with other circles you should checkout the following page.. http://blogs.love2d.org/content/circle-collisions, it's pretty cool stuff.

Cesar · May 2016

@antix I think you can use hitTestPoint() as Circle class inherits from Sprite class. Thank you anyway.

keszegh · May 2016

@Cesar, hitTestPoint() only tests against the bounding box of the sprite, so it won't work properly for a circle.

talis · May 2016

As you can see in this threat also, whenever your buttons will be round not rectangular you can have some miss clicks with normal hitTestPoint() . (As button class is inheriting sprite)
http://giderosmobile.com/forum/discussion/3595/non-rectangle-button/p1

Cesar · May 2016

Thank you very much for the observation

antix · May 2016

@Cesar, Also if you are going to make many circles you could optimize things a little..

	for i = 1,sides do
                local rad, sin, cos = math.rad, math.sin, math.cos
		local angle = rad(i*angleStep)
		local xx = cos(angle)*radius	
		local yy = sin(angle)*radius	
		self:lineTo(xx,yy)	
	end

Making things local makes a difference

chuz0 · May 2016

For round buttons I use the Vector2 class; I just check the e.x,e.y:distanceTo(center_of_button), if it's shorter than the radius it's a hit.

SinisterSoft · May 2016

@antix, will not making the functions local to the function rather than local to the loop be faster - I've not checked what bytecode will be produced.

antix · May 2016

@chuz0, care to share your solution?

@SinisterSoft, you are most likely right. Hmm, I have MANY things to change in my codebase

SinisterSoft · May 2016

I'm not sure if making things local to the app is the same speed as local to the function. It may be.

chuz0 · May 2016

@antix, sure, take a look here : http://giderosmobile.com/tools/vector2
I've used the method in the past, and probably it's not the most effective solution but it worked

Something like this :

game = Core.class(Sprite)
  function game:init()
 
  button = Bitmap.new(Texture.new("roundbutton.png",true))
  button:setAnchorPoint(.5,.5)
  button:setPosition(100,100)
 
 
  self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self)
 
  end
 
function game:onMouseUp(event)
  local v = Vector2.new(e.x,e.y)
  if v:distanceTo(button:getX(),button:getY())<=button:getWidth()/2 then
      print("button touched")
  end
 
end

I haven't tried but it should work.

antix · May 2016

@chuz0 cheers, I had not previously seen the vector2 library . I still will stick with mine since it doesn't need to do a math.sqrt

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