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SDK Development Discussion
93

Here's a simple class I made to make a scrolling parallax background simple

local pd <const> = playdate
local gfx <const> = pd.graphics

class("Parallax").extends(gfx.sprite)

function Parallax:init()
 Parallax.super.init(self)
 self.layers = {}
end

function Parallax:draw(...)
 gfx.setClipRect(...)
 for _, layer in ipairs(self.layers) do
   local img = layer.image
   -- lock offset to steps of 2 to reduce flashing
   local offset = layer.offset - (layer.offset % 2)
   local w = layer.width
   img:draw(self.x+offset, self.y)
   if offset < 0 or offset > w - self.width then
     if offset > 0 then
       img:draw(self.x+offset-w, self.y)
     else
       img:draw(self.x+offset+w, self.y)
     end
   end
 end
 gfx.clearClipRect()
end

function Parallax:addLayer(img, depth)
 local w, _ = img:getSize()
 local layer = {}
 layer.image = img
 layer.depth = depth
 layer.offset = 0
 layer.width = w
 table.push(self.layers, layer)
end

function Parallax:scroll(delta)
 for _, layer in ipairs(self.layers) do
   layer.offset = math.ring(
     layer.offset + (delta * layer.depth),
     -layer.width, 0
   )
 end
 self:markDirty()
end

it also uses the math.ring function that was posted is this thread somewhere (I can't find it atm)

function math.ring(a, min, max)
  if min > max then
    min, max = max, min
  end
  return min + (a-min)%(max-min)
end

It's simple to use:

img_1 = gfx.image.new("images/parallax-1")
img_2 = gfx.image.new("images/parallax-2")

-- create
local parallax = Parallax()
parallax:setSize(400,240)
parallax:addLayer(img_1, 0.2)
parallax:addLayer(img_2, 0.6)
parallax:add()

-- scroll
parallax:scroll(10)

parallax

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