Tutorial 10 - A Simple Dial Class

Dial.lua

--# Dial
Dial = class()
-- A Dial Class
-- Reefwing Software (www.reefwing.com.au)
--
-- 26 July 2012
-- Version 1.0

function Dial:init(x, y, angle)
   
   -- These parameters are used to customise your Dial
   self.x = x    -- x screen co-ordinate for the dial
   self.y = y    -- y screen co-ordinate for the dial
   self.alignment = CENTER    -- Dial uses CENTER alignment
   self.visible = true        -- Boolean to indicate whether dial is drawn and touches handled
   self.currentAngle = angle or 0  -- Current Angle of the dial in degrees (default 0)
   dialImage = readImage("Dropbox:pDial200px")
   knobImage = readImage("Dropbox:pKnob147px")
   radius = knobImage.width/2       -- Radius of knob circle sprite
   self.width = dialImage.width     -- Defined by the dial sprite width
   self.height = dialImage.height   -- Defined by the dial sprite height
   
end

-- Draw function
function Dial:draw()
    
   -- Codea does not automatically call this method
   if self.visible then
       sprite(dialImage, self.x, self.y)
       pushMatrix()
       rotateDialByDegrees(self.x, self.y, self.currentAngle)
       sprite(knobImage, 0, 0)
       popMatrix()
   end
   
end

-- Touch Handler
function Dial:touched(touch)
    
   -- Codea does not automatically call this method
   --
   -- The pointInCircle() function determines if the touch was
   -- on the dial. This function is contained in RSLibrary.
   --
   -- math.polar(x, y) converts from cartesian co-ordinates (x, y) to polar
   -- co-ordinates (distance, angle). We only use the returned angle not the 
   -- distance. This function is also contained in RSLibrary.
   
   if self.visible and pointInCircle(touch.x, touch.y, self.x, self.y, radius) then
       if touch.state == MOVING then
           _, self.currentAngle = math.polar(touch.x, touch.y, self.x, self.y)
       end
   end
   
end

-- Utility Functions
    
function Dial:reset()
   self.currentAngle = 0
end

function rotateDialByDegrees(centreX, centreY, angle)
   translate(centreX, centreY)
   rotate(angle)
end

Main.lua

--# Main
-- DialDemo
-- Define supported orientations
supportedOrientations(ANY)
-- Use this function to perform your initial setup

function setup()

   -- Project Metadata
   version = 1.0
   saveProjectInfo("Description", "Codea Dial Demonstration")
   saveProjectInfo("Author", "Reefwing Software")
   saveProjectInfo("Date", "26th July 2012")
   saveProjectInfo("Version", version)
   print("DialDemo v"..version.."\n")
   -- Keep an eye on Frame Rate (Frames Per Second, FPS) so we can
   -- compare and contrast different approaches. 
   FPS = 0
   watch("FPS")
   -- Define a new dial = Dial(x, y, angle)
   --
   -- Where: (x, y) are the CENTER co-ordinates of the dial. (default alignment is CENTER).
   --        angle = the current angle (in degrees) of the dial.
   dial = Dial(WIDTH/2, HEIGHT/2, 0)
   -- Create a button which will zero the dial
   -- The Button Class is contained within RSLibrary
   local rbX = WIDTH/2 - dial.width/2
   local rbY = HEIGHT/2 - dial.height - 20
   resetButton = Button("Reset", rbX, rbY, dial.width, 50)
   resetButton.action = function() resetButtonTapped() end
  
end

-- Drawing Functions
function draw()
   -- Update instantaneous FPS
   FPS = math.round(1/DeltaTime)
   -- This sets a black background color 
   background(blackColor)
   -- Draw the dial and reset button
   dial:draw()
   resetButton:draw()
end

function orientationChanged(newOrientation)
   -- If the iPad orientation changes we need to 
   -- adjust object co-ordinates.
   local rbX = WIDTH/2 - dial.width/2
   local rbY = HEIGHT/2 - dial.height - 20
   dial.x, dial.y = WIDTH/2, HEIGHT/2
   resetButton.x, resetButton.y = rbX, rbY
end

-- Handle Touches
function touched(touch)
   dial:touched(touch)
   resetButton:touched(touch)
end

function resetButtonTapped()
   dial:reset()
end

Math_Polar.lua

function math.polar(x, y, originX, originY)

   -- Usage: math.polar(x, y) - origin is assumed at (0, 0)
   --               math.polar(x, y, originX, originY)
   --
   -- This function converts from cartesian co-ordinates (x, y) to
   -- polar co-ordinates (distance, angle) using the two functions:
   --
   --    1. distance = hypot(x, y) - the hypotenuse of a right-angle triangle; and
   --    2. angle = atan2(x, y) - is the arc tangent of y/x in radians.
   --
   -- Since nil evaluates to false in Lua, you can use "or" to assign a default value.
   --
   -- Reefwing Software (www.reefwing.com.au)
   -- Version 1.0

   local oX = originX or 0
   local oY = originY or 0
   local dx = x - oX
   local dy = y - oY
   local distance = math.hypot(dx, dy)
   local angleInDegrees = math.deg(math.atan2(dy, dx))
   -- Functions may return multiple results in Lua.
   return distance, angleInDegrees

end