feat(alerts): add scene-local recent ticker

Model the AlertBox and standalone ticker with shared settings; scene tickers render the in-memory active and queued events without saving history. Keep AlertBox content active-event-only.

Ref: https://obsproject.com/kb/obs-studio-overview

Services/AlertOverlayLayer.cs

@@ -58,6 +58,8 @@ public sealed class AlertOverlayLayer : IDisposable
 
     private ChatMessage? _current;
     private Source? _currentBox;
+    private sealed record TickerFeed(string Text, double Duration);
+    private volatile TickerFeed? _tickerFeed;
     private IAlertClipDecoder? _clip;
     private VideoFrame? _latestClipFrame;
     private bool _clipEof;
@@ -66,8 +68,6 @@ public sealed class AlertOverlayLayer : IDisposable
     private int _clipHeight;
     private bool _clipSawFrame;
     private bool _clipAudioHeard;
-    private string? _tickerText;
-    private AlertDisplayMethod _tickerMethod = AlertDisplayMethod.TickerScroll;
     private double _elapsed;
     private IEnumerable<Scene>? _scenes;
 
@@ -139,6 +139,7 @@ public sealed class AlertOverlayLayer : IDisposable
             BeginClip();
         }
         _contentVersion++;
+        RefreshTickerFeed();
     }
 
     /// <summary>Advance the playback clock (the ticker's beat — and the test seam;
@@ -172,6 +173,7 @@ public sealed class AlertOverlayLayer : IDisposable
                 _current = null;
                 _elapsed = 0;
                 AdvanceToNext();
+                RefreshTickerFeed();
             }
             _contentVersion++;
             return;
@@ -184,6 +186,7 @@ public sealed class AlertOverlayLayer : IDisposable
             _elapsed = 0;
             BeginClip();
             _contentVersion++;
+            RefreshTickerFeed();
             return;
         }
 
@@ -193,6 +196,7 @@ public sealed class AlertOverlayLayer : IDisposable
             _current = null;
             _elapsed = 0;
             AdvanceToNext();
+            RefreshTickerFeed();
         }
         _contentVersion++;
     }
@@ -249,27 +253,55 @@ public sealed class AlertOverlayLayer : IDisposable
     /// <see cref="VideoFrame.OriginX"/>/<see cref="VideoFrame.OriginY"/> instead of
     /// a hardcoded 0. <b>No alert box in the scene means no ticker at all</b> — there
     /// is no longer a global position for it to live in.</para></summary>
-    public VideoFrame? AlertTickerFrame
-    {
-        get
-        {
-            if (_current == null || string.IsNullOrWhiteSpace(_tickerText)) return null;
-            var box = _currentBox;
-            if (box == null) return null;
+    public VideoFrame? AlertTickerFrame => AlertBoxTickerFrame(_currentBox);
 
-            var w = (int)Math.Max(1, Math.Round(box.Width));
-            var h = (int)Math.Max(1, Math.Min(
-                Math.Round(box.Height), AlertTickerRenderer.Height));
-            var frame = AlertTickerRenderer.Render(
-                _tickerText!, _elapsed, _tickerMethod, AlertSeconds(),
-                TickerReadsPerAlert, w, h);
-            return frame == null
-                ? null
-                : new VideoFrame(frame.Width, frame.Height, frame.BgraPixels)
-                {
-                    Placement = ((int)Math.Round(box.X), (int)Math.Round(box.Y)),
-                };
+    public VideoFrame? AlertBoxTickerFrame(Source? alertBox)
+    {
+        if (_current == null || alertBox is not { Type: SourceType.AlertBox }) return null;
+
+        var w = (int)Math.Max(1, Math.Round(alertBox.Width));
+        var h = (int)Math.Max(1, Math.Min(
+            Math.Round(alertBox.Height), AlertTickerRenderer.Height));
+        var frame = AlertTickerRenderer.Render(
+            alertBox.Ticker, ComposeTicker(_current), _elapsed, AlertSeconds(),
+            TickerReadsPerAlert, w, h);
+        return frame == null
+            ? null
+            : new VideoFrame(frame.Width, frame.Height, frame.BgraPixels)
+            {
+                Placement = ((int)Math.Round(alertBox.X), (int)Math.Round(alertBox.Y)),
+            };
+    }
+
+    public VideoFrame? RenderSceneTicker(Source tickerSource)
+    {
+        if (tickerSource.Type != SourceType.Ticker || !tickerSource.Ticker.IsEnabled)
+            return null;
+
+        var feed = _tickerFeed;
+        if (feed == null) return null;
+        return AlertTickerRenderer.Render(
+            tickerSource.Ticker,
+            feed.Text,
+            _elapsed,
+            feed.Duration,
+            TickerReadsPerAlert,
+            (int)Math.Max(1, Math.Round(tickerSource.Width)),
+            (int)Math.Max(1, Math.Round(tickerSource.Height)));
+    }
+
+    private void RefreshTickerFeed()
+    {
+        if (_current == null)
+        {
+            _tickerFeed = null;
+            return;
         }
+
+        var messages = new[] { _current }.Concat(_queue).ToArray();
+        _tickerFeed = new TickerFeed(
+            string.Join("   •   ", messages.Select(ComposeTicker)),
+            messages.Sum(DurationOf));
     }
 
     /// <summary>How many times the marquee must cross the frame per alert, so the
@@ -354,17 +386,11 @@ public sealed class AlertOverlayLayer : IDisposable
     private void BeginClip()
     {
         StopClip();
-        _tickerText = null;
         if (_current == null) return;
 
         var box = _scenes?.SelectMany(s => s.Elements).OfType<Source>()
             .FirstOrDefault(s => s.Type == SourceType.AlertBox);
         _currentBox = box;
-        if (box != null && box.AlertShowTicker)
-        {
-            _tickerText = ComposeTicker(_current);
-            _tickerMethod = box.AlertDisplayMethod;
-        }
 
         if (box == null) return;
         StartSoundByte(box);
@@ -552,6 +578,9 @@ public sealed class AlertOverlayLayer : IDisposable
             };
             UpdatePreview(alertBox);
         }
+        foreach (var ticker in scenes.SelectMany(s => s.Elements).OfType<Source>()
+                     .Where(s => s.Type == SourceType.Ticker))
+            UpdateTickerPreview(ticker);
     }
 
     private void RefreshAlertPreviews()
@@ -566,6 +595,27 @@ public sealed class AlertOverlayLayer : IDisposable
         foreach (var alertBox in _scenes.SelectMany(s => s.Elements).OfType<Source>()
                      .Where(s => s.Type == SourceType.AlertBox))
             UpdatePreview(alertBox);
+        foreach (var ticker in _scenes.SelectMany(s => s.Elements).OfType<Source>()
+                     .Where(s => s.Type == SourceType.Ticker))
+            UpdateTickerPreview(ticker);
+    }
+
+    private void UpdateTickerPreview(Source ticker)
+    {
+        var frame = RenderSceneTicker(ticker);
+        if (frame == null)
+        {
+            ticker.VideoImageSource = null;
+            return;
+        }
+
+        var bitmap = ticker.VideoImageSource;
+        if (bitmap == null || bitmap.PixelWidth != frame.Width || bitmap.PixelHeight != frame.Height)
+        {
+            bitmap = new WriteableBitmap(frame.Width, frame.Height, 96, 96, PixelFormats.Bgra32, null);
+            ticker.VideoImageSource = bitmap;
+        }
+        bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
     }
 
     public void Dispose()
@@ -574,6 +624,7 @@ public sealed class AlertOverlayLayer : IDisposable
         _ticker?.Stop();
         _queue.Clear();
         _current = null;
+        _tickerFeed = null;
         StopClip();
     }
-}
+}