Don't skip surrogate pairs.

Runtime/ui/painting/canvas_impl.cs

                     layer.draws.Add(CanvasShader.texAlpha(layer, p, mesh, tex));
                 }
                 else {
-                    Paint paintWithWhite = new Paint(p);
-                    paintWithWhite.color = Colors.white;
+                    Paint paintWithWhite = new Paint(p) {color = Colors.white};
                     layer.draws.Add(CanvasShader.tex(layer, paintWithWhite, mesh.resolveMesh(), EmojiUtils.image));
                 }
             };

Runtime/ui/txt/wordbreaker.cs

             this._current = 0;
             this._scanOffset = 0;
             this._inEmailOrUrl = false;
-            this.nextUntilCodePoint();
+            // this.nextUntilCodePoint();
         }
 
         public int current() {
             }
             
             for (; this._current < this._text.size; ++this._current) {
-                this.nextUntilCodePoint();
+                // this.nextUntilCodePoint();
                 if (this._current >= this._text.size) {
                     break;
                 }

Tests/Editor/Paragraph.cs

                             text:
                             "This is FontStyle.italic And 发撒放豆腐sad 发生的 Bold Text This is FontStyle.italic  And Bold  Text\n\n"),
                         new TextSpan(style: new TextStyle(fontSize: 18),
-                            text: "FontSize 18: Get a named matrix value from the shader."),
+                            text: "FontSize 18: Get a named matrix value from the shader.\n\n"),
                         new TextSpan(style: new TextStyle(fontSize: 24),
                             text: "Emoji \ud83d\ude0a\ud83d\ude0b\ud83d\ude0d\ud83d\ude0e\ud83d\ude00"),
                         new TextSpan(style: new TextStyle(fontSize: 14),
                         new TextSpan(style: new TextStyle(fontSize: 18),
-                            text: "Emoji \ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05 Emoji Emoji"),
+                            text: "\ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05"),
-                            text: "Emoji \ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05 Emoji Emoji Emoji"),
+                            text: "\ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05"),
-                            text: "Emoji \ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05"),
+                            text: "\ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05"),
+                        new TextSpan(style: new TextStyle(fontSize: 18),
+                            text: "\ud83d\ude01\ud83d\ude02\ud83d\ude03\ud83d\ude04\ud83d\ude05"),
-                            text: "Emoji \ud83d\ude06\ud83d\ude1C\ud83d\ude18\ud83d\ude2D\ud83d\ude0C\ud83d\ude1EEmoji"),
+                            text: "Emoji \ud83d\ude06\ud83d\ude1C\ud83d\ude18\ud83d\ude2D\ud83d\ude0C\ud83d\ude1E\n\n"),
                         new TextSpan(style: new TextStyle(fontSize: 14),
                             text: "FontSize 14"),
                     })));