Balls Example

 Simple lua code showing event handling, class creation, grabbing objects across the screen, cursor setting...

(Code by Adrien "Adriweb" Bertrand)

<syntaxhighlight>Ball = class()

function Ball:init(x,y,r,color)
self.x = x
self.y = y
self.r = r
self.color = color
self.isActive = false
self.id = #ballsTable+1
end

function Ball:paint(gc)
gc:setColorRGB(unpack(self.color))
gc:fillArc(self.x,self.y,self.r,self.r,0,360)
if self.isActive then
gc:setColorRGB(0)
gc:drawArc(self.x,self.y,self.r,self.r,0,360)
end
end

function Ball:move(x,y)
self.x = x
self.y = y
platform.window:invalidate()
end

function on.grabDown(x,y)
isGrabbing = not isGrabbing
platform.window:invalidate()
end

function on.mouseUp(x,y)
isGrabbing = false
platform.window:invalidate()
end

function on.mouseDown(x,y)
isGrabbing = true
platform.window:invalidate()
end

function on.mouseMove(x,y)
if isGrabbing and (trackedBall and trackedBall.isActive) then
txt2 = "moving ball #"..trackedBall.id
trackedBall:move(x-trackedBall.r/2,y-trackedBall.r/2)
else
txt2 = "not moving anything"
for i,ball in ipairs(ballsTable) do
if math.abs(ball.x+ball.r/2-x) <= ball.r/1.8 and math.abs(ball.y+ball.r/2-y) <= ball.r/1.8 then
ball.isActive = true
trackedBall = ball
else
ball.isActive = false
end
end
end
end

function on.paint(gc)
for _,ball in ipairs(ballsTable) do
ball:paint(gc)
end
gc:setColorRGB(0)
gc:drawString("grabbing : " .. tostring(isGrabbing),2,0,"top")
gc:drawString(tostring(txt2),2,20,"top")
gc:drawString("Press Enter to create a Ball object", 2, 190, "top")
end

ballsTable = {}
grabFlag = false
isGrabbing = false
txt2 = "not moving anything"

function on.enterKey()
ballsTable[#ballsTable+1] = Ball(math.random(10,250), math.random(10,180), 15, {math.random(0,255),math.random(0,255),math.random(0,255)})
end
</syntaxhighlight>