[canvaskit] default to Ahem in flutter_tester emulation mode (flutter…

…#31024)

* [canvaskit] default to Ahem in flutter_tester emulation mode

lib/web_ui/lib/src/engine/canvaskit/text.dart

@@ -32,7 +32,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
           textAlign,
           textDirection,
           maxLines,
-          fontFamily,
+          ui.debugEmulateFlutterTesterEnvironment ? 'Ahem' : fontFamily,
           fontSize,
           height,
           textHeightBehavior,
@@ -43,7 +43,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
           locale,
         ),
         _textDirection = textDirection ?? ui.TextDirection.ltr,
-        _fontFamily = fontFamily,
+        _fontFamily = ui.debugEmulateFlutterTesterEnvironment ? 'Ahem' : fontFamily,
         _fontSize = fontSize,
         _height = height,
         _leadingDistribution = textHeightBehavior?.leadingDistribution,
@@ -228,8 +228,8 @@ class CkTextStyle implements ui.TextStyle {
       fontWeight,
       fontStyle,
       textBaseline,
-      fontFamily,
-      fontFamilyFallback,
+      ui.debugEmulateFlutterTesterEnvironment ? 'Ahem' : fontFamily,
+      ui.debugEmulateFlutterTesterEnvironment ? null : fontFamilyFallback,
       fontSize,
       letterSpacing,
       wordSpacing,
@@ -464,8 +464,8 @@ class CkStrutStyle implements ui.StrutStyle {
     ui.FontWeight? fontWeight,
     ui.FontStyle? fontStyle,
     bool? forceStrutHeight,
-  })  : _fontFamily = fontFamily,
-        _fontFamilyFallback = fontFamilyFallback,
+  })  : _fontFamily = ui.debugEmulateFlutterTesterEnvironment ? 'Ahem' : fontFamily,
+        _fontFamilyFallback = ui.debugEmulateFlutterTesterEnvironment ? null : fontFamilyFallback,
         _fontSize = fontSize,
         _height = height,
         _leadingDistribution = leadingDistribution,

lib/web_ui/test/canvaskit/flutter_tester_emulation_golden_test.dart

@@ -0,0 +1,118 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'common.dart';
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+const ui.Rect kDefaultRegion = ui.Rect.fromLTRB(0, 0, 500, 250);
+
+void testMain() {
+  ui.debugEmulateFlutterTesterEnvironment = true;
+
+  group('flutter_tester emulation', () {
+    setUpCanvasKitTest();
+
+    test('defaults to Ahem font family',
+        () async {
+      final CkPictureRecorder recorder = CkPictureRecorder();
+      final CkCanvas canvas = recorder.beginRecording(kDefaultRegion);
+      canvas.translate(10, 10);
+
+      void _drawTextWithOutline(String text, {
+        String? paragraphFontFamily,
+        String? textFontFamily,
+        List<String>? textFontFallbacks,
+        String? strutStyleFontFamily,
+        List<String>? strutStyleFontFallbacks,
+        double? strutStyleFontSize,
+      }) {
+        final CkStrutStyle? strutStyle;
+
+        if (strutStyleFontFamily != null || strutStyleFontFallbacks != null || strutStyleFontSize != null) {
+          strutStyle = CkStrutStyle(
+            fontFamily: strutStyleFontFamily,
+            fontFamilyFallback: strutStyleFontFallbacks,
+            fontSize: strutStyleFontSize,
+          );
+        } else {
+          strutStyle = null;
+        }
+
+        final CkParagraphBuilder builder = CkParagraphBuilder(CkParagraphStyle(
+          fontFamily: paragraphFontFamily,
+          strutStyle: strutStyle,
+        ));
+
+        final bool needsTextStyle = textFontFamily != null || textFontFallbacks != null;
+
+        if (needsTextStyle) {
+          builder.pushStyle(CkTextStyle(
+            fontFamily: textFontFamily,
+            fontFamilyFallback: textFontFallbacks,
+          ));
+        }
+
+        builder.addText(text);
+
+        if (needsTextStyle) {
+          builder.pop();
+        }
+
+        final CkParagraph paragraph = builder.build();
+        paragraph.layout(const ui.ParagraphConstraints(width: 10000));
+        canvas.drawParagraph(paragraph, ui.Offset.zero);
+        canvas.drawRect(
+          ui.Rect.fromLTWH(-4, -4, paragraph.maxIntrinsicWidth + 8, paragraph.height + 8),
+          CkPaint()
+            ..style = ui.PaintingStyle.stroke
+            ..strokeWidth = 1,
+        );
+        canvas.translate(
+          0,
+          paragraph.height + 16,
+        );
+      }
+
+      _drawTextWithOutline('default');
+      _drawTextWithOutline(
+        'roboto paragraph',
+        paragraphFontFamily: 'Roboto',
+      );
+      _drawTextWithOutline(
+        'roboto text',
+        textFontFamily: 'Roboto',
+      );
+      _drawTextWithOutline(
+        'roboto text fallback',
+        textFontFallbacks: <String>['Roboto'],
+      );
+      _drawTextWithOutline(
+        'roboto strut style',
+        strutStyleFontFamily: 'Roboto',
+        strutStyleFontSize: 40,
+      );
+      _drawTextWithOutline(
+        'roboto strut style fallback',
+        strutStyleFontFallbacks: <String>['Roboto'],
+        strutStyleFontSize: 40,
+      );
+
+      await matchPictureGolden(
+        'canvaskit_defaults_to_ahem.png',
+        recorder.endRecording(),
+        region: kDefaultRegion,
+      );
+    });
+    // TODO(yjbanov): https://github.com/flutter/flutter/issues/60040
+    // TODO(yjbanov): https://github.com/flutter/flutter/issues/71520
+  }, skip: isIosSafari || isFirefox);
+}