Broadcast

src/jsMain/kotlin/nl/astraeus/vst/chip/midi/Broadcaster.kt

@@ -0,0 +1,110 @@
+@file:OptIn(ExperimentalJsExport::class)
+
+package nl.astraeus.vst.chip.midi
+
+import kotlinx.browser.window
+import org.khronos.webgl.Uint8Array
+import org.w3c.dom.BroadcastChannel
+import org.w3c.dom.MessageEvent
+import kotlin.math.min
+
+@JsExport
+enum class MessageType {
+  SYNC,
+  MIDI
+}
+
+@JsExport
+class SyncMessage(
+  @JsName("timeOrigin")
+  val timeOrigin: Double = window.performance.asDynamic().timeOrigin,
+  @JsName("now")
+  val now: Double = window.performance.now()
+) {
+  @JsName("type")
+  val type: String = MessageType.SYNC.name
+}
+
+// time -> syncOrigin
+// receive syn message
+// syncOrigin = my timeOrigin - sync.timeOrigin
+// - sync.timeOrigin = 50
+// - my.timeOrigin = 100
+// - syncOrigin = -50
+
+// - sync.timeOrigin = 49
+// - my.timeOrigin = 100
+// - syncOrigin = update to -51
+
+@JsExport
+class MidiMessage(
+  @JsName("data")
+  val data: Uint8Array,
+  @JsName("timestamp")
+  val timestamp: dynamic = null,
+  @JsName("timeOrigin")
+  val timeOrigin: dynamic = window.performance.asDynamic().timeOrigin
+) {
+  @JsName("type")
+  val type = MessageType.MIDI.name
+}
+
+object Sync {
+  var syncOrigin = 0.0
+
+  fun update(sync: SyncMessage) {
+    syncOrigin = min(syncOrigin, window.performance.asDynamic().timeOrigin - sync.timeOrigin)
+  }
+
+  fun now(): Double = window.performance.now() + syncOrigin
+}
+
+object Broadcaster {
+  val channels = mutableMapOf<Int, BroadcastChannel>()
+
+  fun getChannel(channel: Int): BroadcastChannel = channels.getOrPut(channel) {
+    println("Opening broadcast channel $channel")
+    val bcChannel = BroadcastChannel("audio-worklet-$channel")
+
+    bcChannel.onmessage = { event ->
+      onMessage(channel, event)
+    }
+
+    bcChannel
+  }
+
+  private fun onMessage(channel: Int, event: MessageEvent) {
+    val data: dynamic = event.data.asDynamic()
+
+    console.log(
+      "Received broadcast message on channel $channel",
+      event
+    )
+    if (data.type == MessageType.SYNC.name) {
+      val syncMessage = SyncMessage(
+        data.timeOrigin,
+        data.now
+      )
+      Sync.update(syncMessage)
+    } else {
+      console.log(
+        "Received broadcast message on channel $channel",
+        event,
+        window.performance,
+        window.performance.now() - event.timeStamp.toDouble()
+      )
+    }
+  }
+
+  fun send(channel: Int, message: Any) {
+    console.log("Sending broadcast message on channel $channel:", message)
+    getChannel(channel).postMessage(message)
+  }
+
+  fun sync() {
+    for (channel in channels.values) {
+      channel.postMessage(SyncMessage())
+    }
+  }
+
+}