first commit

lib/knife/behavior.lua

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+-- behavior.lua -- a state manager
+
+-- internal/external api
+
+local function getCurrentFrame (behavior)
+    return behavior.states[behavior.state][behavior.index]
+end
+
+local function advanceFrame (behavior)
+    local nextState = behavior.frame.after
+    local nextIndex = behavior.index + 1
+    local maxIndex = #behavior.states[behavior.state]
+
+    if nextState then
+        behavior.state = nextState
+        nextIndex = 1
+    elseif nextIndex > maxIndex then
+        nextIndex = 1
+    end
+
+    behavior.index = nextIndex
+    behavior.frame = behavior:getCurrentFrame()
+end
+
+local function performAction (behavior)
+    local act = behavior.frame.action
+
+    if act then
+        act(behavior, behavior.subject)
+    end
+end
+
+-- external api
+
+local function update (behavior, dt)
+    behavior.elapsed = behavior.elapsed + dt
+
+    while behavior.elapsed >= behavior.frame.duration do
+        behavior.elapsed = behavior.elapsed - behavior.frame.duration
+        behavior:advanceFrame()
+        behavior:performAction()
+    end
+
+    return behavior
+end
+
+local function setState (behavior, state, index)
+    behavior.state = state
+    behavior.index = index or 1
+    behavior.elapsed = 0
+    behavior.frame = behavior:getCurrentFrame()
+    behavior:performAction()
+    return behavior
+end
+
+-- behavior factory
+
+return function (states, subject)
+    local behavior = {
+        states = states,
+        subject = subject,
+        elapsed = 0,
+        state = 'default',
+        index = 1,
+        -- internal api
+        getCurrentFrame = getCurrentFrame,
+        advanceFrame = advanceFrame,
+        performAction = performAction,
+        -- external api
+        update = update,
+        setState = setState
+    }
+
+    behavior.frame = behavior:getCurrentFrame()
+    behavior:performAction()
+
+    return behavior
+end