[vector_graphics][vector_graphics_compiler] Fix text-anchor and tspan gap with adjacent <tspan>s (#11637)

## Summary

`<text x="..." text-anchor="middle"><tspan>ABCDEFG</tspan><tspan>ABCDEFG</tspan></text>` rendered noticeably differently from the equivalent single-tspan `<tspan>ABCDEFGABCDEFG</tspan>`: the two-tspan version was shifted right past the anchor *and* had a visible space between the two tspans. Two independent root causes, fixed in two separate places.

**1. `vector_graphics` — anchor applies per-chunk, not per-tspan.** The listener was independently offsetting each tspan's paragraph by `dx - paragraphWidth * xAnchorMultiplier`. Per the SVG spec, `text-anchor` applies to the entire anchored chunk (the contiguous run of glyphs whose start is established by an explicit `x`/`y`), not to each tspan in isolation. The listener now buffers per-tspan paragraphs within a chunk, flushes on the next explicit position update or on `toPicture()`, and applies the anchor offset to the chunk total. `text-anchor="start"` behavior is unchanged. A new TextPosition with `x` (or `reset=true`) starts a new chunk; bare per-tspan TextPositions emitted by the parser do not.

**2. `vector_graphics_compiler` — parser injected a spurious space between adjacent tspans.** `_appendText` had a "previous element was a tspan ⇒ prepend a space" rule that fired regardless of whether the source actually had whitespace at the boundary. So `<tspan>A</tspan><tspan>B</tspan>` parsed to `['A', ' B']` (the visible gap), even though every browser parses it to `'AB'`. Replaced with a rule that only prepends when whitespace truly exists at the boundary — either as a leading-whitespace prefix on the current text, or as an earlier whitespace-only text event we've now flagged.

Tests added on both sides:
- `vector_graphics/test/listener_test.dart`: `Text anchor middle centers the entire chunk across tspans` — drives the listener with a two-tspan middle-anchored chunk (including the parser's bare per-tspan TextPosition between them) and asserts the second tspan starts at the original x.
- `vector_graphics_compiler/test/parser_test.dart`: `adjacent tspans without whitespace are not separated by a space` and `adjacent tspans with whitespace between still get a space` — locks down both branches of the new parser rule.

Both packages bumped to `1.2.1` with CHANGELOG entries.

Fixes flutter/flutter#185927

## Before / After

| SVG | Before (buggy) | After (this PR) |
| --- | --- | --- |
| **svg1** (single tspan)<br>`<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" fill="none">`<br>&nbsp;&nbsp;`<text x="100" y="50" text-anchor="middle" fill="#FF0000">`<br>&nbsp;&nbsp;&nbsp;&nbsp;`<tspan>ABCDEFGABCDEFG</tspan>`<br>&nbsp;&nbsp;`</text>`<br>`</svg>`<br><br>**svg2** (two tspans)<br>`<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" fill="none">`<br>&nbsp;&nbsp;`<text x="100" y="50" text-anchor="middle" fill="#FF0000">`<br>&nbsp;&nbsp;&nbsp;&nbsp;`<tspan>ABCDEFG</tspan><tspan>ABCDEFG</tspan>`<br>&nbsp;&nbsp;`</text>`<br>`</svg>` | <img width="390" height="844" alt="image" src="https://github.com/user-attachments/assets/7ffbe594-d821-4b4c-b759-c5fb61a61339" /> | <img width="780" height="1688" alt="image" src="https://github.com/user-attachments/assets/076b69fb-2bfc-490a-9669-566e45f7e9a2" /> |

## Test plan

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: fondoger

packages/vector_graphics/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 1.2.2
+
+* Fixes `text-anchor` on `<text>` with multiple `<tspan>` children. The
+  anchor now applies to the entire anchored chunk as required by the SVG
+  spec, instead of independently to each tspan.
+
 ## 1.2.1
 
 * Fixes uncaught `StateError` and `NoSuchMethodError` from `useHtmlRenderObject()` on CanvasKit / iOS Safari so SVG widgets fall back to the HTML render object.

packages/vector_graphics/lib/src/listener.dart

@@ -274,6 +274,20 @@ class FlutterVectorGraphicsListener extends VectorGraphicsCodecListener {
   double _textPositionY = 0;
   Float64List? _textTransform;
 
+  // Pending text draws within the current SVG anchored chunk. Per the SVG
+  // spec, `text-anchor` applies to the chunk as a whole, so we cannot
+  // commit a paragraph to the canvas until we know the full chunk width.
+  final List<_PendingTextDraw> _pendingChunk = <_PendingTextDraw>[];
+  // The user-space x at which the current chunk begins (i.e. the value of
+  // `_accumulatedTextPositionX` at the time the first paragraph in the
+  // chunk was queued). Null when no chunk is open.
+  double? _chunkOriginX;
+  // The text-anchor multiplier of the first paragraph in the chunk; used
+  // to position the chunk as a whole.
+  double _chunkAnchorMultiplier = 0;
+  // Cumulative pen-advance within the current chunk so far.
+  double _chunkAdvance = 0;
+
   _PatternConfig? _currentPattern;
 
   static final Paint _emptyPaint = Paint();
@@ -294,6 +308,7 @@ class FlutterVectorGraphicsListener extends VectorGraphicsCodecListener {
   PictureInfo toPicture() {
     assert(!_done);
     _done = true;
+    _flushPendingTextChunk();
     try {
       return PictureInfo._(_recorder.endRecording(), _size);
     } finally {
@@ -652,6 +667,15 @@ class FlutterVectorGraphicsListener extends VectorGraphicsCodecListener {
   @override
   void onUpdateTextPosition(int textPositionId) {
     final _TextPosition position = _textPositions[textPositionId];
+    // Per the SVG spec, a new anchored chunk begins only when the element
+    // establishes an explicit absolute position (i.e. an `x` or `y` on a
+    // <text> or <tspan>). Relative `dx`/`dy` move the pen but do NOT
+    // start a new chunk; neither does the bare per-tspan TextPosition the
+    // parser emits when the tspan has no x/y of its own. `reset` (set on
+    // <text> elements) likewise starts a fresh chunk.
+    if (position.reset || position.x != null || position.y != null) {
+      _flushPendingTextChunk();
+    }
     if (position.reset) {
       _accumulatedTextPositionX = 0;
       _textPositionY = 0;
@@ -685,9 +709,26 @@ class FlutterVectorGraphicsListener extends VectorGraphicsCodecListener {
     final _TextConfig textConfig = _textConfig[textId];
     final double dx = _accumulatedTextPositionX ?? 0;
     final double dy = _textPositionY;
-    double paragraphWidth = 0;
 
-    void draw(int paintId) {
+    // A change in text-anchor on a continuing chunk also starts a new
+    // anchored chunk per the SVG spec.
+    if (_pendingChunk.isNotEmpty &&
+        textConfig.xAnchorMultiplier != _chunkAnchorMultiplier) {
+      _flushPendingTextChunk();
+    }
+
+    if (_pendingChunk.isEmpty) {
+      _chunkOriginX = dx;
+      _chunkAnchorMultiplier = textConfig.xAnchorMultiplier;
+      _chunkAdvance = 0;
+    } else {
+      // Continuing the chunk: take the live pen position so any in-chunk
+      // relative `dx="..."` movements applied via onUpdateTextPosition
+      // since the last segment are accounted for in the segment's offset
+      // within the chunk.
+      _chunkAdvance = dx - _chunkOriginX!;
+    }
+    Paragraph buildParagraph(int paintId) {
       final Paint paint = _paints[paintId];
       if (patternId != null) {
         paint.shader = _patterns[patternId]!.shader;
@@ -707,37 +748,56 @@ class FlutterVectorGraphicsListener extends VectorGraphicsCodecListener {
           decorationColor: textConfig.decorationColor,
         ),
       );
-
       builder.addText(textConfig.text);
-
       final Paragraph paragraph = builder.build();
       paragraph.layout(const ParagraphConstraints(width: double.infinity));
-      paragraphWidth = paragraph.maxIntrinsicWidth;
+      return paragraph;
+    }
+
+    double paragraphWidth = 0;
+    if (fillId != null) {
+      final Paragraph p = buildParagraph(fillId);
+      paragraphWidth = p.maxIntrinsicWidth;
+      _pendingChunk.add(_PendingTextDraw(p, _chunkAdvance, dy, _textTransform));
+    }
+    if (strokeId != null) {
+      final Paragraph p = buildParagraph(strokeId);
+      paragraphWidth = p.maxIntrinsicWidth;
+      _pendingChunk.add(_PendingTextDraw(p, _chunkAdvance, dy, _textTransform));
+    }
+
+    _chunkAdvance += paragraphWidth;
+    _accumulatedTextPositionX = dx + paragraphWidth;
+  }
 
-      if (_textTransform != null) {
+  void _flushPendingTextChunk() {
+    if (_pendingChunk.isEmpty) {
+      return;
+    }
+    final double originX = _chunkOriginX ?? 0;
+    final double anchorOffset = _chunkAdvance * _chunkAnchorMultiplier;
+    for (final _PendingTextDraw draw in _pendingChunk) {
+      final Paragraph paragraph = draw.paragraph;
+      if (draw.transform != null) {
         _canvas.save();
-        _canvas.transform(_textTransform!);
+        _canvas.transform(draw.transform!);
       }
       _canvas.drawParagraph(
         paragraph,
         Offset(
-          dx - paragraph.maxIntrinsicWidth * textConfig.xAnchorMultiplier,
-          dy - paragraph.alphabeticBaseline,
+          originX + draw.offsetWithinChunk - anchorOffset,
+          draw.dy - paragraph.alphabeticBaseline,
         ),
       );
       paragraph.dispose();
-      if (_textTransform != null) {
+      if (draw.transform != null) {
         _canvas.restore();
       }
     }
-
-    if (fillId != null) {
-      draw(fillId);
-    }
-    if (strokeId != null) {
-      draw(strokeId);
-    }
-    _accumulatedTextPositionX = dx + paragraphWidth;
+    _pendingChunk.clear();
+    _chunkOriginX = null;
+    _chunkAnchorMultiplier = 0;
+    _chunkAdvance = 0;
   }
 
   int _createImageKey(int imageId, int format) {
@@ -885,6 +945,20 @@ class _TextConfig {
   final Color decorationColor;
 }
 
+class _PendingTextDraw {
+  _PendingTextDraw(
+    this.paragraph,
+    this.offsetWithinChunk,
+    this.dy,
+    this.transform,
+  );
+
+  final Paragraph paragraph;
+  final double offsetWithinChunk;
+  final double dy;
+  final Float64List? transform;
+}
+
 /// An exception thrown if decoding fails.
 ///
 /// The [originalException] is a detailed exception about what failed in

packages/vector_graphics/pubspec.yaml

@@ -2,7 +2,7 @@ name: vector_graphics
 description: A vector graphics rendering package for Flutter using a binary encoding.
 repository: https://github.com/flutter/packages/tree/main/packages/vector_graphics
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+vector_graphics%22
-version: 1.2.1
+version: 1.2.2
 
 environment:
   sdk: ^3.9.0

packages/vector_graphics/test/listener_test.dart

@@ -120,6 +120,9 @@ void main() {
     listener.onTextConfig('foo', null, 0, 0, 16, 0, 0, 0, 0);
     await listener.onDrawText(0, 0, null, null);
     await listener.onDrawText(0, 0, null, null);
+    // Force flush of the pending anchored chunk by starting a new one.
+    listener.onTextPosition(1, 0, 0, null, null, true, null);
+    listener.onUpdateTextPosition(1);
 
     final Invocation drawParagraph0 = factory.fakeCanvases.last.invocations[0];
     final Invocation drawParagraph1 = factory.fakeCanvases.last.invocations[1];
@@ -133,6 +136,62 @@ void main() {
     expect((drawParagraph1.positionalArguments[1] as Offset).dx, 58);
   });
 
+  test('Text anchor middle centers the entire chunk across tspans', () async {
+    // SVG: <text x="100" y="50" text-anchor="middle">
+    //        <tspan>ABCDEFG</tspan><tspan>ABCDEFG</tspan>
+    //      </text>
+    // Per SVG spec, the concatenation of both tspans forms a single
+    // anchored chunk that should be centered around x=100.
+    final factory = TestPictureFactory();
+    final listener = FlutterVectorGraphicsListener(pictureFactory: factory);
+    listener.onPaintObject(
+      color: const ui.Color(0xffff0000).toARGB32(),
+      strokeCap: null,
+      strokeJoin: null,
+      blendMode: BlendMode.srcIn.index,
+      strokeMiterLimit: null,
+      strokeWidth: null,
+      paintStyle: ui.PaintingStyle.fill.index,
+      id: 0,
+      shaderId: null,
+    );
+    listener.onTextPosition(0, 100, 50, null, null, true, null);
+    listener.onUpdateTextPosition(0);
+    // xAnchorMultiplier = 0.5 corresponds to text-anchor="middle".
+    listener.onTextConfig('ABCDEFG', null, 0.5, 0, 16, 0, 0, 0, 0);
+    await listener.onDrawText(0, 0, null, null);
+    // The parser emits a TextPosition for every <tspan>, including those
+    // with no x/y. That must NOT break the current anchored chunk.
+    listener.onTextPosition(1, null, null, null, null, false, null);
+    listener.onUpdateTextPosition(1);
+    listener.onTextConfig('ABCDEFG', null, 0.5, 0, 16, 0, 0, 0, 1);
+    await listener.onDrawText(1, 0, null, null);
+    // Force flush of the pending anchored chunk by starting a new one.
+    listener.onTextPosition(2, 0, 0, null, null, true, null);
+    listener.onUpdateTextPosition(2);
+
+    final Invocation drawParagraph0 = factory.fakeCanvases.last.invocations[0];
+    final Invocation drawParagraph1 = factory.fakeCanvases.last.invocations[1];
+    expect(drawParagraph0.memberName, #drawParagraph);
+    expect(drawParagraph1.memberName, #drawParagraph);
+
+    final double dx0 = (drawParagraph0.positionalArguments[1] as Offset).dx;
+    final double dx1 = (drawParagraph1.positionalArguments[1] as Offset).dx;
+
+    // The chunk is two equal tspans of width w. text-anchor="middle" centers
+    // the whole chunk (total width 2w) around x=100, so:
+    //   dx0 = 100 - w   (left tspan)
+    //   dx1 = 100       (right tspan)
+    // Therefore the second tspan should start exactly at the original x=100.
+    expect(dx1, 100, reason: 'second tspan should start at the original x');
+    final double w = 100 - dx0;
+    expect(
+      dx1 - dx0,
+      w,
+      reason: 'tspans should be contiguous within the chunk',
+    );
+  });
+
   test('should assert when imageId is invalid', () async {
     final factory = TestPictureFactory();
     final listener = FlutterVectorGraphicsListener(pictureFactory: factory);

packages/vector_graphics_compiler/CHANGELOG.md

@@ -1,3 +1,11 @@
+## 1.2.3
+
+* Fixes the SVG parser injecting a spurious space between adjacent
+  `<tspan>` elements that have no whitespace between them in the source.
+  Previously `<tspan>A</tspan><tspan>B</tspan>` was emitted as `"A"` +
+  `" B"`, producing a visible gap; it now emits `"A"` + `"B"` to match
+  every browser.
+
 ## 1.2.2
 
 * Adds support for modern space-separated HSL and HSLA color syntax.

packages/vector_graphics_compiler/lib/src/svg/parser.dart

@@ -758,16 +758,23 @@ class SvgParser {
     final textHasNonWhitespace = text.trim() != '';
 
     // Not from the spec, but seems like how Chrome behaves.
-    // - If `x` is specified, don't prepend whitespace.
-    // - If the last element was a tspan and we're dealing with some
-    //   non-whitespace data, prepend a space.
-    // - If the last text wasn't whitespace and ended with whitespace, prepend
-    //   a space.
+    // - If `x` is specified on the current element, don't prepend whitespace.
+    // - Otherwise prepend a space if either:
+    //     * the previous text emission ended on a space character, or
+    //     * we are following a `</tspan>` and the source actually contains
+    //       whitespace at the boundary (either as a leading-whitespace prefix
+    //       on this text or as an earlier whitespace-only text event that
+    //       was trimmed).
+    //   The "tspan" gate is what prevents `<tspan>A</tspan><tspan>B</tspan>`
+    //   from rendering as "A B" — without it the parser would always inject
+    //   a space between adjacent tspans even when no whitespace exists in
+    //   the source.
+    final bool textHasLeadingWhitespace =
+        text.isNotEmpty && _whitespacePattern.matchAsPrefix(text) != null;
+    final followsTspan = _lastEndElementEvent?.localName == 'tspan';
     final bool prependSpace =
         _currentAttributes.x == null &&
-            (_lastEndElementEvent?.localName == 'tspan' &&
-                textHasNonWhitespace) ||
-        _lastTextEndedWithSpace;
+        (_lastTextEndedWithSpace || (followsTspan && textHasLeadingWhitespace));
 
     _lastTextEndedWithSpace =
         textHasNonWhitespace &&
@@ -785,6 +792,12 @@ class SvgParser {
         .replaceAll(_contiguousSpaceMatcher, ' ');
 
     if (text.isEmpty) {
+      // A pure-whitespace text event sitting between two sibling tspans
+      // still needs to flag that whitespace existed, so the next
+      // non-empty text can prepend a space.
+      if (textHasLeadingWhitespace && followsTspan) {
+        _lastTextEndedWithSpace = true;
+      }
       return;
     }
 

packages/vector_graphics_compiler/pubspec.yaml

@@ -2,7 +2,7 @@ name: vector_graphics_compiler
 description: A compiler to convert SVGs to the binary format used by `package:vector_graphics`.
 repository: https://github.com/flutter/packages/tree/main/packages/vector_graphics_compiler
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+vector_graphics%22
-version: 1.2.2
+version: 1.2.3
 
 executables:
   vector_graphics_compiler:

packages/vector_graphics_compiler/test/parser_test.dart

@@ -277,6 +277,42 @@ void main() {
     ]);
   });
 
+  test('adjacent tspans without whitespace are not separated by a space', () {
+    // Regression test: previously the parser unconditionally injected a
+    // space between the text of any two consecutive tspans, even when the
+    // source XML contained no whitespace between </tspan> and <tspan>.
+    // That caused `<tspan>A</tspan><tspan>B</tspan>` to render as "A B"
+    // (a visible gap), instead of "AB" as every browser does.
+    const svg = '''
+<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100">
+<text x="100" y="50" text-anchor="middle"><tspan>ABCDEFG</tspan><tspan>HIJKLMN</tspan></text>
+</svg>''';
+
+    final VectorInstructions instructions = parseWithoutOptimizers(svg);
+
+    expect(instructions.text.map((TextConfig t) => t.text), <String>[
+      'ABCDEFG',
+      'HIJKLMN',
+    ]);
+  });
+
+  test('adjacent tspans with whitespace between still get a space', () {
+    // Sibling case to the regression test above: when there *is* source
+    // whitespace between </tspan> and <tspan>, that whitespace must be
+    // preserved as a single space prepended to the second tspan.
+    const svg = '''
+<svg xmlns="http://www.w3.org/2000/svg" width="100" height="50">
+<text x="0" y="40"><tspan>A</tspan> <tspan>B</tspan></text>
+</svg>''';
+
+    final VectorInstructions instructions = parseWithoutOptimizers(svg);
+
+    expect(instructions.text.map((TextConfig t) => t.text), <String>[
+      'A',
+      ' B',
+    ]);
+  });
+
   test('stroke-opacity', () {
     const strokeOpacitySvg = '''
 <svg viewBox="0 0 10 10" fill="none">