lib: add link-time/spring

1 files changed, 64 insertions, 1 deletions

diff --git a/alv-lib/link-time.moon b/alv-lib/link-time.moon
index 251ee6c..a043516 100644
--- a/alv-lib/link-time.moon
+++ b/alv-lib/link-time.moon
@@ -314,7 +314,7 @@ ad = Constant.meta
       delta = 0
 
       if trigger
-        @state = -attack
+        @state = if attack > 0 then -attack else decay
       elseif clock
         return if @state == 0
 
@@ -341,6 +341,68 @@ ad = Constant.meta
 
     vis: => type: 'bar', bar: @.out!
 
+spring = Constant.meta
+  meta:
+    name: 'spring'
+    summary: "Integrate impulses using easing"
+    examples: { '(spring [clock] evt0 [evt1…])' }
+    description: "
+Every arriving `evt` triggers an impulse that is integrated as `clock` ticks.
+Returns a num~ stream that starts at 0.
+
+- `clock` should be a `link/clock~` stream. This argument can be omitted
+  and the stream be passed as a dynamic definition in `*clock*` instead.
+- `evt!` are !-streams of structs.
+  The following struct keys can be specified:
+  - `amp`: amplitude of the impulse
+  - `dur`: duration of the impulse (beats)"
+
+  value: class extends Op
+    pattern = -evt['link/clock'] + evt!*0
+    setup: (inputs, scope) =>
+      { clock, events } = pattern\match inputs
+
+      super
+        clock: Input.hot clock or scope\get '*clock*'
+        events: [Input.hot e for e in *events]
+
+      @state or= { offset: 0, events: {} }
+      @setup_out '~', T.num, @state.offset
+
+    tick: =>
+      for inp in *@inputs.events
+        if evt = inp!
+          evt = {
+            i: 0
+            amp: evt.amp or 1
+            dur: evt.dur or 1
+            -- ease: evt.ease or "quad.out"
+          }
+          @state.events[evt] = true
+
+      if clock = @inputs.clock!
+        pre = clock.state\beat_at_time clock.time - clock.dt, 1
+        post = clock.state\beat_at_time clock.time, 1
+        delta = post - pre
+
+        accum = 0
+        for evt in pairs @state.events
+          evt.i += delta / evt.dur
+
+          if evt.i >= 1
+            @state.offset += evt.amp
+            @state.events[evt] = nil
+          elseif evt.i >= 0
+            t = evt.i
+
+            -- quad.out
+            -- t = 1 - t
+            -- t = 1 - t * t
+
+            accum += t * evt.amp
+
+        @out\set @state.offset + accum
+
 Constant.meta
   meta:
     name: 'link-time'
@@ -355,3 +417,4 @@ Constant.meta
     :phase
     :decay
     :ad
+    :spring