envelopes

1 files changed, 29 insertions, 0 deletions

diff --git a/lib/envelope.moon b/lib/envelope.moon
new file mode 100644
index 0000000..0129eb4
--- /dev/null
+++ b/lib/envelope.moon
@@ -0,0 +1,29 @@
+import Const, Op, Scope, eval from require 'core'
+
+class ar_core extends Op
+  @doc: "(ar-core attack release gate)
+((ar attack release) gate) - AR envelope
+
+goes from 0 to 1 in attack seconds, holds while gate is on, then goes back to 0 in release seconds."
+
+  new: (...) =>
+    super ...
+    @value = 0
+
+  setup: (@a, @r, @gate) =>
+    assert @a, "ar requires an attack value"
+    assert @r, "ar requires a release value"
+    assert @gate, "ar requires a gate value"
+
+  update: (dt) =>
+    @a\update dt
+    @r\update dt
+    @gate\update dt
+
+    slope = if @gate\get! then @a\getc! else -@r\getc!
+
+    @value = math.min 1, math.max 0, @value + dt / slope
+
+scope = Scope.from_table { 'ar-core': ar_core }
+scope\set 'ar', eval '(fn (a r) (fn (gate) (ar-core a r gate)))', scope
+scope