Fix path bounds for multiple rects. Implement winding rules (flutter#18165)

Author: ferhatb

lib/web_ui/dev/goldens_lock.yaml

@@ -1,2 +1,2 @@
 repository: https://github.com/flutter/goldens.git
-revision: 790616cbfb269fe17d44840ce52ec187fff5f9a7
+revision: 0c1a793bfd49e30fccdd7ad64329a114a9cb32f7

lib/web_ui/lib/src/engine/canvas_pool.dart

@@ -501,8 +501,14 @@ class _CanvasPool extends _SaveStackTracking {
   /// 'Runs' the given [path] by applying all of its commands to the canvas.
   void _runPath(html.CanvasRenderingContext2D ctx, SurfacePath path) {
     ctx.beginPath();
-    for (Subpath subpath in path.subpaths) {
-      for (PathCommand command in subpath.commands) {
+    final List<Subpath> subpaths = path.subpaths;
+    final int subpathCount = subpaths.length;
+    for (int subPathIndex = 0; subPathIndex < subpathCount; subPathIndex++) {
+      final Subpath subpath = subpaths[subPathIndex];
+      final List<PathCommand> commands = subpath.commands;
+      final int commandCount = commands.length;
+      for (int c = 0; c < commandCount; c++) {
+        final PathCommand command = commands[c];
         switch (command.type) {
           case PathCommandTypes.bezierCurveTo:
             final BezierCurveTo curve = command;
@@ -587,7 +593,7 @@ class _CanvasPool extends _SaveStackTracking {
 
   void drawPath(ui.Path path, ui.PaintingStyle style) {
     _runPath(context, path);
-    contextHandle.paint(style);
+    contextHandle.paintPath(style, path.fillType);
   }
 
   void drawShadow(ui.Path path, ui.Color color, double elevation,
@@ -756,6 +762,18 @@ class ContextStateHandle {
     }
   }
 
+  void paintPath(ui.PaintingStyle style, ui.PathFillType pathFillType) {
+    if (style == ui.PaintingStyle.stroke) {
+      context.stroke();
+    } else {
+      if (pathFillType == ui.PathFillType.nonZero) {
+        context.fill();
+      } else {
+        context.fill('evenodd');
+      }
+    }
+  }
+
   void reset() {
     context.fillStyle = '';
     // Read back fillStyle/strokeStyle values from context so that input such

lib/web_ui/lib/src/engine/surface/path.dart

@@ -1005,22 +1005,22 @@ class SurfacePath implements ui.Path {
             break;
           case PathCommandTypes.rect:
             final RectCommand cmd = op;
-            left = cmd.x;
+            minX = cmd.x;
             double width = cmd.width;
             if (cmd.width < 0) {
-              left -= width;
+              minX -= width;
               width = -width;
             }
-            double top = cmd.y;
+            minY = cmd.y;
             double height = cmd.height;
             if (cmd.height < 0) {
-              top -= height;
+              minY -= height;
               height = -height;
             }
-            curX = minX = left;
-            maxX = left + width;
-            curY = minY = top;
-            maxY = top + height;
+            curX = minX;
+            maxX = minX + width;
+            curY = minY;
+            maxY = minY + height;
             break;
           case PathCommandTypes.rRect:
             final RRectCommand cmd = op;

lib/web_ui/lib/src/engine/surface/recording_canvas.dart

@@ -440,19 +440,22 @@ class RecordingCanvas {
         return;
       }
     }
-    _hasArbitraryPaint = true;
-    _didDraw = true;
-    ui.Rect pathBounds = path.getBounds();
-    final double paintSpread = _getPaintSpread(paint);
-    if (paintSpread != 0.0) {
-      pathBounds = pathBounds.inflate(paintSpread);
+    SurfacePath sPath = path;
+    if (sPath.subpaths.isNotEmpty) {
+      _hasArbitraryPaint = true;
+      _didDraw = true;
+      ui.Rect pathBounds = sPath.getBounds();
+      final double paintSpread = _getPaintSpread(paint);
+      if (paintSpread != 0.0) {
+        pathBounds = pathBounds.inflate(paintSpread);
+      }
+      // Clone path so it can be reused for subsequent draw calls.
+      final ui.Path clone = SurfacePath._shallowCopy(path);
+      final PaintDrawPath command = PaintDrawPath(clone, paint.paintData);
+      _paintBounds.grow(pathBounds, command);
+      clone.fillType = sPath.fillType;
+      _commands.add(command);
     }
-    // Clone path so it can be reused for subsequent draw calls.
-    final ui.Path clone = SurfacePath._shallowCopy(path);
-    final PaintDrawPath command = PaintDrawPath(clone, paint.paintData);
-    _paintBounds.grow(pathBounds, command);
-    clone.fillType = path.fillType;
-    _commands.add(command);
   }
 
   void drawImage(ui.Image image, ui.Offset offset, SurfacePaint paint) {

lib/web_ui/test/golden_tests/engine/canvas_winding_rule_test.dart

@@ -0,0 +1,72 @@
+// 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.
+
+// @dart = 2.6
+import 'dart:html' as html;
+
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart';
+import 'package:test/test.dart';
+
+import 'package:web_engine_tester/golden_tester.dart';
+
+void main() async {
+  final Rect region = Rect.fromLTWH(0, 0, 500, 500);
+
+  BitmapCanvas canvas;
+
+  setUp(() {
+    canvas = BitmapCanvas(region);
+  });
+
+  tearDown(() {
+    canvas.rootElement.remove();
+  });
+
+  test('draws paths using nonzero and evenodd winding rules', () async {
+    paintPaths(canvas);
+    html.document.body.append(canvas.rootElement);
+    await matchGoldenFile('canvas_path_winding.png', region: region);
+  });
+
+}
+
+void paintPaths(BitmapCanvas canvas) {
+  canvas.drawRect(Rect.fromLTRB(0, 0, 500, 500),
+      SurfacePaintData()
+        ..color = Color(0xFFFFFFFF)
+        ..style = PaintingStyle.fill); // white
+
+  SurfacePaint paintFill = SurfacePaint()
+    ..style = PaintingStyle.fill
+    ..color = Color(0xFF00B0FF);
+  SurfacePaint paintStroke = SurfacePaint()
+    ..style = PaintingStyle.stroke
+    ..strokeWidth = 2
+    ..color = Color(0xFFE00000);
+  Path path1 = Path()
+    ..fillType = PathFillType.evenOdd
+    ..moveTo(50, 0)
+    ..lineTo(21, 90)
+    ..lineTo(98, 35)
+    ..lineTo(2, 35)
+    ..lineTo(79, 90)
+    ..close()
+    ..addRect(Rect.fromLTWH(20, 100, 200, 50))
+    ..addRect(Rect.fromLTWH(40, 120, 160, 10));
+  Path path2 = Path()
+    ..fillType = PathFillType.nonZero
+    ..moveTo(50, 200)
+    ..lineTo(21, 290)
+    ..lineTo(98, 235)
+    ..lineTo(2, 235)
+    ..lineTo(79, 290)
+    ..close()
+    ..addRect(Rect.fromLTWH(20, 300, 200, 50))
+    ..addRect(Rect.fromLTWH(40, 320, 160, 10));
+  canvas.drawPath(path1, paintFill.paintData);
+  canvas.drawPath(path2, paintFill.paintData);
+  canvas.drawPath(path1, paintStroke.paintData);
+  canvas.drawPath(path2, paintStroke.paintData);
+}

lib/web_ui/test/path_test.dart

@@ -128,6 +128,16 @@ void main() {
     expect(path.getBounds(), const Rect.fromLTRB(50, 60, 50, 60));
   });
 
+  test('Should compute bounds for multiple addRect calls', () {
+    final Path emptyPath = Path();
+    expect(emptyPath.getBounds(), Rect.zero);
+
+    final SurfacePath path = SurfacePath();
+    path.addRect(Rect.fromLTWH(0, 0, 270, 45));
+    path.addRect(Rect.fromLTWH(134.5, 0, 1, 45));
+    expect(path.getBounds(), const Rect.fromLTRB(0, 0, 270, 45));
+  });
+
   test('Should compute bounds for lines', () {
     final SurfacePath path = SurfacePath();
     path.moveTo(25, 30);