Support animations

[jcmoyer]

API concepts:

• Animation (sequence of frames by duration)
• Frame (rectangle with a duration and optional collection of attachments)
• Animation set (a set of animations)
• Animation script (a script that specifies a set of animations - see below)
• Animation data (immutable description of an animation set that multiple independent animation sets can refer to)

Animation sets can be created programmatically or described inline using a DSL.

Ideal look'n'feel:

-- create animation set programmatically
local as = aset.new()
local walk = as:addanimation('walk')
local f = walk:addframe(x,y,w,h,duration) -- duration can be in a format like '0.1s' or '100ms'
f:addattachment('lefthand',x,y)
walk:addframe(x,y,w,h,duration)
walk:addframe(x,y,w,h,duration)

as:play('walk')

function love.update(dt)
  -- animation sets need to be able to flip frames so they need to know about time passing
  as:update(dt)
end
function love.draw()
  local offsx, offsy = as:attachment('lefthand')
  love.graphics.draw(sword, objx + offsx, objy + offsy)
  love.graphics.draw(player, objx, objy, as:frame())
end

-- there should be a DSL module to make this look more descriptive
-- this module should let you load from a file:
local as = dsl.loadfile('path/to/anim/script.lua')

-- or describe it inline:
local as = dsl.run(function()
  animation 'idle' {
    frame {
      source = {x,y,w,h}, duration = '0.1s',
      attachments = {
        lefthand = {16,16}
      }
      -- alternately?: attachment 'lefthand' {16,16}
    },
    frame { ... }
  }
  animation 'walk' { ... }
end)

Things I've found a need for during LD32 and will be adding:

• [x] Arbitrary userdata stored per frame
  • Because I didn't have time to plan this out ahead of time I ended up storing bullet radius in an attachment as the X component - yuck
  • Userdata is just a generalization of attachments
• [x] Quads stored per frame
  • Generally useful for rendering from image to screen based on the source of a frame
  • How do we get the reference width and height?
• [x] Animator states like 'playing', 'paused', etc.
• [x] Way to know if an animator has played through an animation once, or maybe a way to have an animator stop animating once it has gone through an animation
  • Should probably use an event emitter implementation, see #22
• [ ] More animation options?
  • repeat = 'none|once|pingpong' | 123 | false?
  • next = 'otheranimationname'?
  • Can be specified at the animation 'name' {...} level
• [x] Allow extending of the DSL function environment.
• [ ] Convenience function to load animation sets from love.filesystem? I used this model in LD27.
• [ ] Write tests

[jcmoyer]

Work has begun on the feature/animation branch.

[jcmoyer]

I'm going to merge everything so far (79d71d5fde970b77707013ebd2af61c6726e023e) into master then work on the rest post-LD33. Shouldn't be any breaking changes.