Pico-8 Animation Operators

Code for combining simple animations together to create more complex animations using + and * operators. 

The operator code plus the example combined are under 1k compressed bytes. The operators alone are 370 compressed bytes.

The example uses four simple animations—each one just a different coloured circle starting in a different corner and moving to the diagonally opposite corner—and combines them in different ways to create the final animation. 

For simple animations A and B:

• The + operators first runs A and, once it's finished, runs B.
•  The * operator runs both A and B at the same time.

As with normal addition and multiplication you can string together as many animations as you want and use parentheses to indicate a particular ordering.

To create animations use `new_animation()` and then give the animation object an `init` method. The `init` method should return a table containing a `draw` and an `update` function; `update` should return true when the animation has finished.

a = new_animation()
a.init = function()
   local offset = 0
   return {
      update=function()
         offset += 5
         if offset > 128 then
            return true
         end
      end,
      draw=function()
         circfill(offset, offset, 2, 7)
      end
   }
end

The animation object then needs to be instantiated to use it.

anim = a() -- or a.init(), same thing
function _update()
   anim.update()
end
function _draw()
   cls()
   anim.draw()
end

Having the `init` function means you can use the same animation multiple times since any internal values, like `offset`, will be re-initialized each time. You don't need to initialize the animation each time when combining animations, that's handled internally, you only need to initialize the combined animation as a whole.

-- creates a compound animation which will play the simple
-- animation three times in a row.
anim = (a + a + a)() -- or (a + a + a).init()