nimforum mirror - UIRELAYS query with threads

nelsonqt (orginal) [2026-06-01T15:54:11+02:00] view original

I'm setting up POC to imitate DAW (nano) with LV2 loaded.

The only way I could get uirelays running on separate thread was to initialise in main. I ran the updates in separate thread. which I guess is how daws work.

Main is DAW (host) in my example. I think this should be okay as DAW runs many Lv2 and I understand it provides orchestration of Lv2 GUI / Audio thread.

I took the hello world example from uirealy and split it apart.

The last thing I'm not sure of how can I pass data, lets says a parameter float value for gain - from UI thread to Audio thread?

Bear in mind in a real daw there will several Lv2/VST but they will handle non-blocking audio thread as well as data transfer - I expect it will need to handle something for databinding from UI to LV2 audio, VST audio and so on. Eventually Many to Many but happy to work with abstact LV2 for now with 1 audio thread.

With this example, gain value from UI thread to Audio thread.

I appreciate this UI lib uses callbacks so thinking of hooking into handleEvent() to pass values. LV2 uses Atom messages with ports to communicate with host - the host sends the parameter to Audio DSP.


import uirelays

# Global state
var layout: ScreenLayout
var width, height: int
var fm: FontMetrics
var font: Font
var mouseX, mouseY = 0
var clickMsg = "Click anywhere"

proc initPlugin*() =
  ## Called once when plugin loads
  layout = createWindow(640, 480)
  width = layout.width
  height = layout.height
  font = openFont("", 18, fm)  # empty path = platform default font
  setWindowTitle("Hello uirelays")

proc handleEvents*() =
  ## Call this when host sends events (mouse, keyboard, etc.)
  var e: Event
  while pollEvent(e):
    case e.kind
    of QuitEvent, WindowCloseEvent:
      discard  # Host controls this
    of WindowResizeEvent:
      width = e.x
      height = e.y
    of MouseDownEvent:
      mouseX = e.x
      mouseY = e.y
      clickMsg = "Clicked at " & $e.x & ", " & $e.y
      if e.button == RightButton:
        clickMsg &= " (right)"
    of KeyDownEvent:
      if e.key == KeyEsc or (e.key == KeyQ and CtrlPressed in e.mods):
        discard  # Host controls quit
    else: discard

proc drawFrame*() =
  ## Call this when host requests a redraw
  let bg = color(30, 30, 46)
  let fg = color(205, 214, 244)
  let accent = color(137, 180, 250)
  let pink = color(245, 194, 231)
  let green = color(166, 227, 161)
  
  # background
  fillRect(rect(0, 0, width, height), bg)
  
  # title bar
  fillRect(rect(0, 0, width, 40), color(49, 50, 68))
  discard drawText(font, 12, 10, "Hello, uirelays!", fg, color(49, 50, 68))
  
  # colored boxes
  fillRect(rect(40, 60, 120, 80), accent)
  fillRect(rect(180, 60, 120, 80), pink)
  fillRect(rect(320, 60, 120, 80), green)
  
  # labels
  discard drawText(font, 60, 90, "Accent", bg, accent)
  discard drawText(font, 205, 90, "Pink", bg, pink)
  discard drawText(font, 345, 90, "Green", bg, green)
  
  # diagonal lines
  for i in 0 ..< 8:
    let x = 40 + i * 20
    drawLine(x, 170, x + 100, 270, accent)
  
  # click feedback
  discard drawText(font, 40, 300, clickMsg, fg, bg)
  
  # instructions
  discard drawText(font, 40, height - 40,
    "Press ESC or Ctrl+Q to quit", color(128, 128, 148), bg)
  
  refresh()

proc shutdownPlugin*() =
  ## Called when plugin unloads
  closeFont(font)
  shutdown()

# --- VST Simulation: Main Thread for DAW, UI and Audio on Worker Threads ---
when isMainModule:
  var uiThread: Thread[void]
  var audioThread: Thread[void]
  var audioRunning = true
  var uiRunning = true
  
  proc uiProcessor() {.gcsafe.} =
    echo "    → UI Thread: Running GUI event loop..."
    
    var frameCount = 0
    
    # UI event loop on worker thread (init already done on main)
    while uiRunning and frameCount < 300:
      {.cast(gcsafe).}:
        handleEvents()
        drawFrame()
      
      {.cast(gcsafe).}:
        sleep(16)
      frameCount.inc
    
    echo "    → UI Thread: Complete"
  
  proc audioProcessor() {.gcsafe.} =
    echo "    → Audio Thread: Started"
    var sampleCount = 0
    
    while audioRunning and sampleCount < 5000:
      # Simulate audio processing
      sampleCount += 1024
      #How can I pass a parameter to the audio thread from the UI thread?   float parameter based on a UI interaction say gain value.
      
      # Real-time audio work (non-blocking)
      {.cast(gcsafe).}:
        sleep(8)
    
    echo "    → Audio Thread: Complete (processed " & $sampleCount & " samples)"
  
  proc main() =
    echo "Simulating VST Plugin...running in daw."
    echo ""
    echo "Thread Layout:"
    echo "  → Main Thread: DAW/VST Host (reserved)"
    
    # Initialize uirelays on MAIN thread (requirement)
    echo ""
    echo "  → Initializing plugin on main thread..."
    initPlugin()
    
    # Spawn UI thread
    echo "  → Spawning UI thread..."
    createThread(uiThread, uiProcessor)
    
    # Spawn audio thread
    echo "  → Spawning audio thread..."
    createThread(audioThread, audioProcessor)
    
    # Main thread is now available for DAW/VST host
    echo ""
    echo "  Main thread: Available for DAW/VST host callbacks"
    sleep(6000)  # ~6 seconds
    
    # Signal threads to stop
    echo ""
    echo "  → Signaling worker threads to shutdown..."
    uiRunning = false
    audioRunning = false
    
    # Wait for both threads to finish
    joinThread(uiThread)
    joinThread(audioThread)
    
    # Shutdown on main thread
    echo "  → Shutting down plugin on main thread..."
    shutdownPlugin()
    
    echo ""
    echo "VST plugin simulation complete."
  
  main()

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13952 :: UIRELAYS query with threads - passing data