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DrawCanvas.lua

DrawCanvas = class()

function DrawCanvas:init(x)
    
    -- create an off screen image to hold what is being drawn
    self.canvas = image(1024, 768)
    
    -- set the default pen color, this will change for each line drawn
    self.penColor = color(255, 255, 255, 255)
    
    -- get image for particle
    self.particle = nil
    http.request("http://goo.gl/xV6ha",
        function(theImage, status, head) 
            self.particle=theImage
        end
        )
    
    -- the size of the particles that make up the line
    self.minSize = 32
    self.maxSize = 64
    self.size = self.minSize
    self.step = 0.5
    
    self.frame = 0
    
    -- boolean that determines whether to allow drawing or now
    self.drawing = false
    self.drawingCount = 0
    
end



-- enable drawing n the canvas
function DrawCanvas:startDrawing()
    self.drawing = true
end

-- disable drawing on the canvas
function DrawCanvas:stopDrawing()
    self.drawing = false
end

-- called each frame by codea
function DrawCanvas:draw()

    -- use screen context to obtain touch coordinates
    setContext()
    spriteMode(CENTER)
    
    -- get the angle of the touch vector
    px = CurrentTouch.prevX
    py = CurrentTouch.prevY

    dx = CurrentTouch.deltaX
    dy = CurrentTouch.deltaY
    dh = math.sqrt(dx*dx + dy*dy)
    angle = math.atan2(dy, dx)
    
    -- increment particle size as the line gets longer up to a m self.size = self.size  self.step
    
    self.size = self.size + self.step
    
    psize = -1 * self.size * math.sin(math.log(self.size*self.size))
    
    -- flip from increase to decrease
    if(self.size>self.maxSize or self.size<self.minSize) then
        self.step = self.step * - 1
    end
    
    -- switch to canvas and set color
    setContext(self.canvas)
    blendMode(ADDITIVE)
    tint(self.penColor)
    
    -- loop through each point of of dh vector adding particles so we get a relatively smooth line
    nx = 0
    ny = 0
    if self.drawing then
    for h = 0, dh, 2 do
        ax = math.floor(h * math.cos(angle))
        ay = math.floor(h * math.sin(angle))
        nx = px+ax
        ny = py+ay
        
        -- draw onto canvas
        --sprite("Dropbox:particle flare", nx, ny, psize, psize)
        sprite(self.particle, nx, ny, psize, psize)
    end
    end
    
    -- switch back to screen context and copy contents of canvas to it

    noTint()
    setContext()
    blendMode(ADDITIVE)
    background(0, 0, 0, 255)
    spriteMode(CORNER)
    sprite(self.canvas, 0, 0)
    

end

function DrawCanvas:touched(touch)
    
    -- switch pen color at the start of each touch
    if(touch.state==BEGAN) then
        self.size = 32
        self:startDrawing()
        self.penColor = color(math.random(100,255), math.random(100,255), math.random(100,255), 25)
    end
        
    -- dont update if we are not drawing    
    if(touch.state==ENDED) then
        self:stopDrawing()
        self.size = self.minSize
    end

end

FPS.lua

function FPS()
    return math.floor((1/DeltaTime) + 0.5)
end

Main.lua

    
function setup()
    dc = DrawCanvas()
    parameter.watch("FPS()")
end

function draw()
    dc:draw()
end

function touched(touch)
    dc:touched(touch)
end