Merge pull request #398 from codymullins/shared-glyph-cache

Introduce the concept of a shared glyph cache

Author: JimBobSquarePants

src/ImageSharp.Drawing/Processing/DrawingCanvas{TPixel}.cs

@@ -59,6 +59,12 @@ public sealed class DrawingCanvas<TPixel> : DrawingCanvas
     /// </summary>
     private readonly Stack<DrawingCanvasState> savedStates = new();
 
+    // Per-canvas glyph-outline cache: hoists RichTextGlyphRenderer's per-glyph outline cache from
+    // per-DrawText-call scope up to the whole canvas, so a glyph outline built once is reused by
+    // every DrawText call on this canvas (across a frame's many text runs) instead of being
+    // rebuilt for every run on a text-heavy page.
+    private readonly Dictionary<RichTextGlyphRenderer.CacheKey, List<RichTextGlyphRenderer.GlyphRenderData>> glyphCache = [];
+
     /// <summary>
     /// Initializes a new instance of the <see cref="DrawingCanvas{TPixel}"/> class.
     /// </summary>
@@ -457,7 +463,7 @@ private void DrawTextCore(
         EnsureTextPaint(brush, pen);
 
         RichTextOptions configuredOptions = ConfigureTextOptions(textOptions, path, out IPath? configuredPath);
-        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, configuredPath, pen, brush);
+        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, configuredPath, pen, brush, this.glyphCache);
         TextRenderer renderer = new(glyphRenderer);
         renderer.RenderText(text, configuredOptions);
 
@@ -487,7 +493,7 @@ public override void DrawText(
             effectiveOptions.ShapeOptions,
             Matrix4x4.CreateTranslation(location.X, location.Y, 0) * effectiveOptions.Transform);
 
-        using RichTextGlyphRenderer glyphRenderer = new(placedOptions, path: null, pen, brush);
+        using RichTextGlyphRenderer glyphRenderer = new(placedOptions, path: null, pen, brush, this.glyphCache);
         textBlock.RenderTo(glyphRenderer, wrappingLength);
 
         this.DrawTextOperations(glyphRenderer.DrawingOperations, placedOptions, state.ClipPaths);
@@ -509,7 +515,7 @@ public override void DrawText(
         DrawingCanvasState state = this.ResolveState();
         DrawingOptions effectiveOptions = state.Options;
 
-        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, path, pen, brush);
+        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, path, pen, brush, this.glyphCache);
         textBlock.RenderTo(glyphRenderer, wrappingLength);
 
         this.DrawTextOperations(glyphRenderer.DrawingOperations, effectiveOptions, state.ClipPaths);
@@ -537,7 +543,7 @@ public override void DrawText(
             effectiveOptions.ShapeOptions,
             Matrix4x4.CreateTranslation(location.X, location.Y, 0) * effectiveOptions.Transform);
 
-        using RichTextGlyphRenderer glyphRenderer = new(placedOptions, path: null, pen, brush);
+        using RichTextGlyphRenderer glyphRenderer = new(placedOptions, path: null, pen, brush, this.glyphCache);
         lineLayout.RenderTo(glyphRenderer);
 
         this.DrawTextOperations(glyphRenderer.DrawingOperations, placedOptions, state.ClipPaths);
@@ -558,7 +564,7 @@ public override void DrawText(
         DrawingCanvasState state = this.ResolveState();
         DrawingOptions effectiveOptions = state.Options;
 
-        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, path, pen, brush);
+        using RichTextGlyphRenderer glyphRenderer = new(effectiveOptions, path, pen, brush, this.glyphCache);
         lineLayout.RenderTo(glyphRenderer);
 
         this.DrawTextOperations(glyphRenderer.DrawingOperations, effectiveOptions, state.ClipPaths);
@@ -1144,6 +1150,9 @@ public override void Dispose()
                 this.DisposePendingImageResources();
             }
 
+            // Release the per-canvas glyph-outline cache.
+            this.glyphCache.Clear();
+
             this.isDisposed = true;
         }
     }

src/ImageSharp.Drawing/Processing/RichTextGlyphRenderer.cs

@@ -72,8 +72,10 @@ internal sealed partial class RichTextGlyphRenderer : BaseGlyphBuilder, IDisposa
     // Benchmarked to give <0.2% image difference vs. uncached, with >60% cache hit ratio.
     private const float AccuracyMultiple = 8;
 
-    /// <summary>Maps cache keys to their list of <see cref="GlyphRenderData"/> entries (one per layer).</summary>
-    private readonly Dictionary<CacheKey, List<GlyphRenderData>> glyphCache = [];
+    /// <summary>Maps cache keys to their list of <see cref="GlyphRenderData"/> entries (one per layer).
+    /// Owned by the enclosing <see cref="DrawingCanvas{TPixel}"/> and shared across every DrawText
+    /// call on that canvas, so glyph outlines persist beyond a single text draw.</summary>
+    private readonly Dictionary<CacheKey, List<GlyphRenderData>> glyphCache;
 
     /// <summary>Read cursor into the cached layer list for layered cache hits.</summary>
     private int cacheReadIndex;
@@ -107,16 +109,20 @@ internal sealed partial class RichTextGlyphRenderer : BaseGlyphBuilder, IDisposa
     /// <param name="path">Optional path to draw the text along.</param>
     /// <param name="pen">Default pen for outlined text, or <see langword="null"/> for fill-only.</param>
     /// <param name="brush">Default brush for filled text, or <see langword="null"/> for outline-only.</param>
+    /// <param name="glyphCache">Caller-owned per-canvas glyph cache shared across renderer
+    /// instances so glyph outlines persist beyond a single text draw.</param>
     public RichTextGlyphRenderer(
         DrawingOptions drawingOptions,
         IPath? path,
         Pen? pen,
-        Brush? brush)
+        Brush? brush,
+        Dictionary<CacheKey, List<GlyphRenderData>> glyphCache)
         : base(drawingOptions.Transform)
     {
         this.drawingOptions = drawingOptions;
         this.defaultPen = pen;
         this.defaultBrush = brush;
+        this.glyphCache = glyphCache;
         this.DrawingOperations = [];
         this.currentCompositionMode = drawingOptions.GraphicsOptions.AlphaCompositionMode;
         this.currentBlendingMode = drawingOptions.GraphicsOptions.ColorBlendingMode;
@@ -782,7 +788,7 @@ private void Dispose(bool disposing)
         {
             if (disposing)
             {
-                this.glyphCache.Clear();
+                // The glyph cache is owned by the canvas and outlives this renderer.
                 this.DrawingOperations.Clear();
             }
 
@@ -795,7 +801,7 @@ private void Dispose(bool disposing)
     /// path and the sub-pixel deltas needed to reposition the path at a different
     /// screen location on a cache hit.
     /// </summary>
-    private struct GlyphRenderData
+    internal struct GlyphRenderData
     {
         /// <summary>
         /// The fractional-pixel offset between the path's bounding-box origin
@@ -834,7 +840,7 @@ private struct GlyphRenderData
     /// sub-pixel position (quantized to <see cref="AccuracyMultiple"/>), and the pen reference
     /// (since stroke width affects the outline path).
     /// </summary>
-    private readonly struct CacheKey : IEquatable<CacheKey>
+    internal readonly struct CacheKey : IEquatable<CacheKey>
     {
         /// <summary>Gets the font family name.</summary>
         public string Font { get; init; }