playground: add webaudio_minimal_beep

Author: pthom

bindings/imgui_bundle/demos_python/playground/examples/examples.json

@@ -85,6 +85,10 @@
       {
         "label": "WebGL: 3D cube rendered to a texture",
         "filename": "webgl_texture_in_image.py"
+      },
+      {
+        "label": "WebAudio: Minimal Beep",
+        "filename": "webaudio_minimal_beep.py"
       }
     ]
 }

bindings/imgui_bundle/demos_python/playground/examples/webaudio_minimal_beep.py

@@ -0,0 +1,80 @@
+"""
+WebAudio: minimal beep — Pyodide sanity check.
+
+**Pyodide only.** Calls the browser's WebAudio API via Python's `js` interop.
+Click **Beep** to hear a short sine tone whose frequency and duration you
+can slide.
+
+Why this exists: confirms that audio works in the Pyodide playground
+without needing an SDL2-audio-enabled build or a Python audio binding.
+Same pattern as the `webgl_minimal_mandelbrot.py` demo, just talking to
+`AudioContext` instead of `WebGL2RenderingContext`.
+
+## Gotcha
+
+Browsers require a *user gesture* before an `AudioContext` is allowed to
+produce sound. We create the context lazily inside the Beep button
+handler — the button click is the gesture, so playback starts on the
+very first press.
+"""
+from imgui_bundle import imgui, immapp
+
+
+_audio_ctx = None       # js AudioContext (Pyodide); None on desktop or until first click
+_frequency = 440.0      # Hz
+_duration_ms = 200      # ms
+_status = ""            # last-action message shown under the controls
+
+
+def _ensure_audio_context():
+    """Lazy-init the browser's AudioContext on first call. No-op on desktop."""
+    global _audio_ctx, _status
+    if _audio_ctx is not None:
+        return _audio_ctx
+    try:
+        from js import AudioContext  # type: ignore[import-not-found,import-untyped]
+        _audio_ctx = AudioContext.new()
+        _status = "AudioContext ready"
+    except Exception as e:
+        _status = f"AudioContext unavailable: {e}"
+    return _audio_ctx
+
+
+def _beep():
+    global _status
+    ctx = _ensure_audio_context()
+    if ctx is None:
+        return
+    try:
+        osc = ctx.createOscillator()
+        gain = ctx.createGain()
+        osc.type = "sine"
+        osc.frequency.value = _frequency
+        now = ctx.currentTime
+        end = now + _duration_ms / 1000.0
+        # Short attack/release ramp avoids speaker-click on start/stop
+        gain.gain.setValueAtTime(0.0, now)
+        gain.gain.linearRampToValueAtTime(0.3, now + 0.01)
+        gain.gain.linearRampToValueAtTime(0.0, end)
+        osc.connect(gain)
+        gain.connect(ctx.destination)
+        osc.start(now)
+        osc.stop(end + 0.05)
+        _status = f"Beep @ {_frequency:.0f} Hz for {_duration_ms} ms"
+    except Exception as e:
+        _status = f"Beep failed: {e}"
+
+
+def gui():
+    global _frequency, _duration_ms
+    imgui.text("WebAudio sanity check (Pyodide only)")
+    imgui.separator()
+    _, _frequency = imgui.slider_float("Frequency (Hz)", _frequency, 80.0, 2000.0)
+    _, _duration_ms = imgui.slider_int("Duration (ms)", _duration_ms, 50, 1000)
+    if imgui.button("Beep"):
+        _beep()
+    if _status:
+        imgui.text_disabled(_status)
+
+
+immapp.run(gui, window_title="WebAudio beep", window_size=(500, 220))