List of rectangles

Author: manuelbl

CLAUDE.md

@@ -46,7 +46,7 @@ Version 3 is a complete rewrite (≈10x faster, more standard-compliant) of what
 
 ## Architecture
 
-`QrCode` is the only substantial public surface: immutable factory methods (`EncodeText`, `EncodeTextAdvanced`, `EncodeBinary`, `EncodeSegments`, `EncodeTextInMultipleCodes`) plus rendering (`ToSvgString`, `ToGraphicsPath`, `ToPngBitmap`, `ToBmpBitmap`, `GetModule`). It holds a single `BitMatrix` of modules. Almost all real work lives in `internal` types.
+`QrCode` is the only substantial public surface: immutable factory methods (`EncodeText`, `EncodeTextAdvanced`, `EncodeBinary`, `EncodeSegments`, `EncodeTextInMultipleCodes`) plus rendering (`ToSvgString`, `ToGraphicsPath`, `ToPngBitmap`, `ToBmpBitmap`, `ToRectangles`, `GetModule`). It holds a single `BitMatrix` of modules. Almost all real work lives in `internal` types. The one other public type is the `QrRectangle` value struct returned by `ToRectangles`.
 
 ### Encoding pipeline
 
@@ -78,7 +78,7 @@ Everything is keyed by `version` (1–40) and `ecc` (0–3 = L/M/Q/H). The large
 
 ### Rendering and diagnostics
 
-- `Graphics` (SVG/XAML path, BMP) and `PngBuilder` (PNG) take the finished modules; `QrCode` delegates to them. The SVG path merges adjacent dark modules into the largest rectangles to shrink output.
+- `RectangleBuilder` merges adjacent dark modules into the largest rectangles (greedy, non-overlapping, union == dark modules) to shrink output. It is the single source of truth for that geometry: `QrCode.ToRectangles` exposes the list publicly (as `QrRectangle`s, in `GetModule` coordinates with no border), and `SvgBuilder` (SVG document + SVG/XAML path) consumes the same list, adding the border at emit time. `BmpBuilder` (BMP) and `PngBuilder` (PNG) take the finished modules directly. `QrCode` delegates to all of them.
 - `StructuredAppend` splits long text across up to 16 linked QR codes (used by `EncodeTextInMultipleCodes`).
 - `EncodingInfo` / `PenaltyScore` are opt-in diagnostics: pass an `EncodingInfo` to capture per-mask penalty breakdowns and the chosen segments. This forces *full* penalty evaluation (disables early-stop), so it is slower — it exists for the `QrCodeAnalyzer` tool, not normal use.
 

QrCodeGenerator/Graphics.cs QrCodeGenerator/BmpBuilder.csQrCodeGenerator/Graphics.cs renamed to QrCodeGenerator/BmpBuilder.cs

@@ -1,4 +1,4 @@
-/*
+/*
  * QR code generator library (.NET)
  *
  * Copyright (c) Manuel Bleichenbacher (MIT License)
@@ -7,14 +7,12 @@
 
 using System;
 using System.Diagnostics.CodeAnalysis;
-using System.Globalization;
-using System.Text;
 
 namespace Net.Codecrete.QrCodeGenerator
 {
-    internal class Graphics
+    internal class BmpBuilder
     {
-        internal Graphics(int size, bool[,] modules)
+        internal BmpBuilder(int size, bool[,] modules)
         {
             _size = size;
             _modules = modules;
@@ -26,45 +24,6 @@ internal Graphics(int size, bool[,] modules)
         // Immutable after constructor finishes.
         private readonly bool[,] _modules;
 
-        internal string ToSvgString(int border, string foreground, string background)
-        {
-            if (border < 0)
-            {
-                throw new ArgumentOutOfRangeException(nameof(border), "Border must be non-negative");
-            }
-
-            var dim = _size + border * 2;
-            var sb = new StringBuilder()
-                .Append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n")
-                .Append("<!DOCTYPE svg PUBLIC \"-//W3C//DTD SVG 1.1//EN\" \"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd\">\n")
-                .Append($"<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\" viewBox=\"0 0 {dim} {dim}\" stroke=\"none\">\n")
-                .Append($"\t<rect width=\"100%\" height=\"100%\" fill=\"{background}\"/>\n")
-                .Append("\t<path d=\"");
-
-            // Work on copy as it is destructive
-            var modules = CopyModules();
-            CreatePath(sb, modules, border);
-
-            return sb
-                .Append($"\" fill=\"{foreground}\"/>\n")
-                .Append("</svg>\n")
-                .ToString();
-        }
-
-        internal string ToGraphicsPath(int border)
-        {
-            if (border < 0)
-            {
-                throw new ArgumentOutOfRangeException(nameof(border), "Border must be non-negative");
-            }
-
-            // Work on copy as it is destructive
-            var modules = CopyModules();
-            var path = new StringBuilder();
-            CreatePath(path, modules, border);
-            return path.ToString();
-        }
-
         [SuppressMessage("csharpsquid", "S3776")]
         internal byte[] ToBmpBitmap(int border, int scale, int foreground, int background)
         {
@@ -227,94 +186,5 @@ internal byte[] ToBmpBitmap(int border, int scale, int foreground, int backgroun
 
             return buf;
         }
-
-        // Append an SVG/XAML path for the QR code to the provided string builder
-        private static void CreatePath(StringBuilder path, bool[,] modules, int border)
-        {
-            // Simple algorithm to reduce the number of rectangles for drawing the QR code
-            // and reduce SVG/XAML size.
-            var size = modules.GetLength(0);
-            for (var y = 0; y < size; y++)
-            {
-                for (var x = 0; x < size; x++)
-                {
-                    if (modules[y, x])
-                    {
-                        DrawLargestRectangle(path, modules, x, y, border);
-                    }
-                }
-            }
-        }
-
-        // Find, draw and clear largest rectangle with (x, y) as the top left corner
-        private static void DrawLargestRectangle(StringBuilder path, bool[,] modules, int x, int y, int border)
-        {
-            var size = modules.GetLength(0);
-
-            var bestW = 1;
-            var bestH = 1;
-            var maxArea = 1;
-
-            var xLimit = size;
-            var iy = y;
-            while (iy < size && modules[iy, x])
-            {
-                var w = 0;
-                while (x + w < xLimit && modules[iy, x + w])
-                {
-                    w++;
-                }
-
-                var area = w * (iy - y + 1);
-                if (area > maxArea)
-                {
-                    maxArea = area;
-                    bestW = w;
-                    bestH = iy - y + 1;
-                }
-                xLimit = x + w;
-                iy++;
-            }
-
-            // append path command
-            if (x != 0 || y != 0)
-            {
-                path.Append(' ');
-            }
-
-            // Different locales use different minus signs.
-            FormattableString pathElement = $"M{x + border},{y + border}h{bestW}v{bestH}h{-bestW}z";
-            path.Append(pathElement.ToString(CultureInfo.InvariantCulture));
-
-            // clear processed modules
-            ClearRectangle(modules, x, y, bestW, bestH);
-        }
-
-        // Clear a rectangle of modules
-        private static void ClearRectangle(bool[,] modules, int x, int y, int width, int height)
-        {
-            for (var iy = y; iy < y + height; iy++)
-            {
-                for (var ix = x; ix < x + width; ix++)
-                {
-                    modules[iy, ix] = false;
-                }
-            }
-        }
-
-        // Create a copy of the modules (in row-major order)
-        private bool[,] CopyModules()
-        {
-            var modules = new bool[_size, _size];
-            for (var y = 0; y < _size; y++)
-            {
-                for (var x = 0; x < _size; x++)
-                {
-                    modules[y, x] = _modules[y, x];
-                }
-            }
-
-            return modules;
-        }
     }
 }

QrCodeGenerator/QrCode.cs

@@ -387,7 +387,7 @@ public bool GetModule(int x, int y)
         /// <param name="background">The background color. Defaults to white.</param>
         public string ToSvgString(int border, string foreground = "#000000", string background = "#ffffff")
         {
-            return AsGraphics().ToSvgString(border, foreground, background);
+            return SvgBuilder.ToSvgString(ToRectangles(), Size, border, foreground, background);
         }
 
         /// <summary>
@@ -413,7 +413,34 @@ public string ToSvgString(int border, string foreground = "#000000", string back
         /// <exception cref="ArgumentOutOfRangeException">Thrown if border is negative</exception>
         public string ToGraphicsPath(int border = 0)
         {
-            return AsGraphics().ToGraphicsPath(border);
+            return SvgBuilder.ToGraphicsPath(ToRectangles(), border);
+        }
+
+        /// <summary>
+        /// Gets the dark modules of this QR code as a list of rectangles.
+        /// <para>
+        /// Adjacent dark modules are merged into larger rectangles so that most rectangles
+        /// cover more than a single module, reducing the number of shapes to draw. This is
+        /// the same set of rectangles used internally to render SVG and XAML output.
+        /// </para>
+        /// <para>
+        /// The rectangles use the same coordinate system as <see cref="GetModule"/>: the
+        /// top-left module is at (x=0, y=0) and each unit is one module (no border is included).
+        /// </para>
+        /// <para>
+        /// The rectangles are non-overlapping and their union is exactly the set of dark modules.
+        /// The order in which the rectangles appear in the list is unspecified.
+        /// </para>
+        /// <para>
+        /// This method is intended for rendering the QR code to graphics formats that are not
+        /// directly supported by this library.
+        /// </para>
+        /// </summary>
+        /// <returns>The list of rectangles covering the dark modules.</returns>
+        /// <seealso cref="QrRectangle"/>
+        public IReadOnlyList<QrRectangle> ToRectangles()
+        {
+            return RectangleBuilder.Build(_modules);
         }
 
         /// <summary>
@@ -434,7 +461,7 @@ public string ToGraphicsPath(int border = 0)
         /// <paramref name="scale"/> is less than 1 or the resulting image is wider than 32,768 pixels.</exception>
         public byte[] ToBmpBitmap(int border = 0, int scale = 1, int foreground = 0x000000, int background = 0xffffff)
         {
-            return AsGraphics().ToBmpBitmap(border, scale, foreground, background);
+            return AsBmpBuilder().ToBmpBitmap(border, scale, foreground, background);
         }
 
         /// <summary>
@@ -467,9 +494,9 @@ public static int RgbColor(byte red, byte green, byte blue)
 
         #region Private helper methods
 
-        private Graphics AsGraphics()
+        private BmpBuilder AsBmpBuilder()
         {
-            return new Graphics(Size, _modules.ToBoolArray());
+            return new BmpBuilder(Size, _modules.ToBoolArray());
         }
 
         #endregion