feat(text): composite shared text rasters in output

Raster static text on UI-thread changes and reuse the same transparent BGRA frame in preview and all compositor paths. Cache text frame identity in the frame-pump signature and invalidate static bakes on edits. Follow OBS text-source conventions: https://obsproject.com/kb/text-sources
2026-11-04 15:01:47 -08:00
parent 58eb640c4e
commit 5c4acf141b
19 changed files with 622 additions and 81 deletions
@@ -0,0 +1,150 @@
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using ytLive.Models;
+
+namespace ytLive.Services;
+
+public sealed class TextOverlayRenderer
+{
+    private const int MaxRasterDimension = 4096;
+    private readonly ConcurrentDictionary<Source, CacheEntry> _cache = new();
+
+    public VideoFrame? RenderFrame(Source source)
+        => _cache.TryGetValue(source, out var entry) ? entry.Frame : null;
+
+    public void Remove(Source source) => _cache.TryRemove(source, out _);
+
+    public void Retain(IEnumerable<Source> sources)
+    {
+        var active = new HashSet<Source>(sources);
+        foreach (var source in _cache.Keys)
+            if (!active.Contains(source))
+                _cache.TryRemove(source, out _);
+    }
+
+    public void UpdatePreview(Source source)
+    {
+        var dispatcher = Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+        {
+            dispatcher.Invoke(() => UpdatePreview(source));
+            return;
+        }
+
+        var config = Capture(source);
+        if (_cache.TryGetValue(source, out var cached) && cached.Config == config)
+        {
+            if (!ReferenceEquals(source.VideoImageSource, cached.Preview))
+                source.VideoImageSource = cached.Preview;
+            return;
+        }
+
+        var frame = Rasterize(config);
+        var bitmap = new WriteableBitmap(frame.Width, frame.Height, 96, 96, PixelFormats.Bgra32, null);
+        bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
+        _cache[source] = new CacheEntry(config, frame, bitmap);
+        source.VideoImageSource = bitmap;
+    }
+
+    private static RenderConfig Capture(Source source) => new(
+        source.TextContent,
+        source.TextFontFamily,
+        source.TextFontSize,
+        source.TextColor,
+        source.TextBold,
+        source.TextItalic,
+        source.TextUnderline,
+        source.TextAlignment,
+        RasterDimension(source.Width),
+        RasterDimension(source.Height));
+
+    private static int RasterDimension(double value) =>
+        double.IsFinite(value) ? (int)Math.Clamp(Math.Ceiling(value), 1, MaxRasterDimension) : 1;
+
+    private static VideoFrame Rasterize(RenderConfig config)
+    {
+        var visual = new DrawingVisual();
+        if (!string.IsNullOrEmpty(config.Content))
+        {
+            using var drawing = visual.RenderOpen();
+            var family = new FontFamily(config.FontFamily);
+            var typeface = new Typeface(
+                family,
+                config.Italic ? FontStyles.Italic : FontStyles.Normal,
+                config.Bold ? FontWeights.Bold : FontWeights.Normal,
+                FontStretches.Normal);
+            var brush = new SolidColorBrush(ParseColor(config.Color));
+            brush.Freeze();
+            var formatted = new FormattedText(
+                config.Content,
+                CultureInfo.CurrentUICulture,
+                FlowDirection.LeftToRight,
+                typeface,
+                config.FontSize,
+                brush,
+                1.0)
+            {
+                MaxTextWidth = config.Width,
+                MaxTextHeight = config.Height,
+                TextAlignment = config.Alignment switch
+                {
+                    TextLayerAlignment.Center => System.Windows.TextAlignment.Center,
+                    TextLayerAlignment.Right => System.Windows.TextAlignment.Right,
+                    _ => System.Windows.TextAlignment.Left,
+                },
+                Trimming = TextTrimming.CharacterEllipsis,
+            };
+            if (config.Underline)
+                formatted.SetTextDecorations(TextDecorations.Underline, 0, config.Content.Length);
+            drawing.DrawText(formatted, new Point(0, 0));
+        }
+
+        var bitmap = new RenderTargetBitmap(config.Width, config.Height, 96, 96, PixelFormats.Pbgra32);
+        bitmap.Render(visual);
+        var pixels = new byte[config.Width * config.Height * 4];
+        bitmap.CopyPixels(pixels, config.Width * 4, 0);
+        UnpremultiplyAlpha(pixels);
+        return new VideoFrame(config.Width, config.Height, pixels);
+    }
+
+    private static Color ParseColor(string hex) =>
+        (Color)ColorConverter.ConvertFromString(hex)!;
+
+    private static void UnpremultiplyAlpha(byte[] pixels)
+    {
+        for (var i = 0; i < pixels.Length; i += 4)
+        {
+            var alpha = pixels[i + 3];
+            if (alpha == 0)
+            {
+                pixels[i] = pixels[i + 1] = pixels[i + 2] = 0;
+                continue;
+            }
+            if (alpha == 255) continue;
+            pixels[i] = Unpremultiply(pixels[i], alpha);
+            pixels[i + 1] = Unpremultiply(pixels[i + 1], alpha);
+            pixels[i + 2] = Unpremultiply(pixels[i + 2], alpha);
+        }
+    }
+
+    private static byte Unpremultiply(byte value, byte alpha) =>
+        (byte)Math.Min(255, (value * 255 + alpha / 2) / alpha);
+
+    private sealed record CacheEntry(RenderConfig Config, VideoFrame Frame, WriteableBitmap Preview);
+
+    private readonly record struct RenderConfig(
+        string Content,
+        string FontFamily,
+        double FontSize,
+        string Color,
+        bool Bold,
+        bool Italic,
+        bool Underline,
+        TextLayerAlignment Alignment,
+        int Width,
+        int Height);
+}