feat: Added Decorator class and HasDecorator mixin (#1781)

The new class allows applying visual filters to canvas drawing operations. It is conceptually similar to the LayerProcessor class, except that it applies directly to a canvas instead of a Picture.

This functionality was extracted from PR #1755.

NB: the guitar image was taken from here, which is a public domain image, i.e. licensed under CC0 1.0.

doc/_sphinx/extensions/flutter_app.css

@@ -127,6 +127,7 @@ button.flutter-app-button:after {
 
 .flutter-app-iframe {
   border: 1px solid #555;
+  display: block;
   height: 350px;
   width: 100%;
 }
@@ -138,7 +139,6 @@ button.flutter-app-button:after {
   float: right;
   margin-left: 6pt;
   padding: 8px;
-  width: 280px;
 }
 
 .flutter-app-infobox button.flutter-app-iframe {
@@ -148,8 +148,7 @@ button.flutter-app-button:after {
 .flutter-app-infobox button.flutter-app-button {
   float: right;
   font-size: 0.85em;
-  margin-bottom: 0;
-  margin-right: 0;
+  margin: 6px 0 0 0;
   min-height: 14pt;
   min-width: 50pt;
 }

doc/_sphinx/extensions/flutter_app.py

@@ -52,6 +52,11 @@ class FlutterAppDirective(SphinxDirective):
               compiled.
           "infobox" - the content will be displayed as an infobox floating on
               the right-hand side of the page.
+
+      :width: - override the default width of an iframe in widget/infobox modes.
+
+      :height: - override the default height of an iframe in widget/infobox
+        modes.
     """
     has_content = True
     required_arguments = 0
@@ -60,6 +65,8 @@ class FlutterAppDirective(SphinxDirective):
         'sources': directives.unchanged,
         'page': directives.unchanged,
         'show': directives.unchanged,
+        'width': directives.unchanged,
+        'height': directives.unchanged,
     }
     # Static list of targets that were already compiled during the build
     COMPILED = []
@@ -89,7 +96,21 @@ class FlutterAppDirective(SphinxDirective):
         iframe_url = _doc_root() + self.html_dir + '/index.html?' + page
         result = []
         if 'widget' in self.modes:
-            result.append(IFrame(src=iframe_url, classes=['flutter-app-iframe']))
+            iframe = IFrame(src=iframe_url, classes=['flutter-app-iframe'])
+            result.append(iframe)
+            styles = []
+            if self.options.get('width'):
+                width = self.options.get('width')
+                if width.isdigit():
+                    width += 'px'
+                styles.append("width: " + width)
+            if self.options.get('height'):
+                height = self.options.get('height')
+                if height.isdigit():
+                    height += 'px'
+                styles.append("height: " + height)
+            if styles:
+                iframe.attributes['style'] = '; '.join(styles)
         if 'popup' in self.modes:
             result.append(Button(
                 '',
@@ -237,8 +258,10 @@ def _doc_root():
 
 class IFrame(nodes.Element, nodes.General):
     def visit(self, node):
-        self.body.append(
-            self.starttag(node, 'iframe', src=node.attributes['src']))
+        attrs = {'src': node.attributes['src']}
+        if 'style' in node.attributes:
+            attrs['style'] = node.attributes['style']
+        self.body.append(self.starttag(node, 'iframe', **attrs).strip())
 
     def depart(self, _):
         self.body.append('</iframe>')

doc/_sphinx/theme/flames.css

@@ -797,3 +797,12 @@ div.admonition.admonition-deprecated {
   --admonition-icon-color: #555;
   --admonition-title-background-color: #1c1c1c;
 }
+
+
+pre, div[class*="highlight-"] {
+  clear: none;
+}
+
+h1, h2, h3, h4, h5, h6 {
+  clear: both;
+}

doc/flame/examples/lib/decorator_blur.dart

@@ -0,0 +1,30 @@
+import 'package:doc_flame_examples/flower.dart';
+import 'package:flame/experimental.dart';
+import 'package:flame/game.dart';
+import 'package:flame/rendering.dart';
+
+class DecoratorBlurGame extends FlameGame with HasTappableComponents {
+  @override
+  Future<void> onLoad() async {
+    var step = 0;
+    add(
+      Flower(
+        size: 100,
+        position: canvasSize / 2,
+        onTap: (flower) {
+          step++;
+          if (step == 1) {
+            flower.decorator = PaintDecorator.blur(3.0);
+          } else if (step == 2) {
+            flower.decorator = PaintDecorator.blur(5.0);
+          } else if (step == 3) {
+            flower.decorator = PaintDecorator.blur(0.0, 20.0);
+          } else {
+            flower.decorator = null;
+            step = 0;
+          }
+        },
+      )..onTapUp(),
+    );
+  }
+}

doc/flame/examples/lib/decorator_grayscale.dart

@@ -0,0 +1,32 @@
+import 'package:doc_flame_examples/flower.dart';
+import 'package:flame/experimental.dart';
+import 'package:flame/game.dart';
+import 'package:flame/rendering.dart';
+
+class DecoratorGrayscaleGame extends FlameGame with HasTappableComponents {
+  @override
+  Future<void> onLoad() async {
+    var step = 0;
+    add(
+      Flower(
+        size: 100,
+        position: canvasSize / 2,
+        onTap: (flower) {
+          step++;
+          if (step == 1) {
+            flower.decorator = PaintDecorator.grayscale();
+          } else if (step == 2) {
+            flower.decorator = PaintDecorator.grayscale(opacity: 0.5);
+          } else if (step == 3) {
+            flower.decorator = PaintDecorator.grayscale(opacity: 0.2);
+          } else if (step == 4) {
+            flower.decorator = PaintDecorator.grayscale(opacity: 0.1);
+          } else {
+            flower.decorator = null;
+            step = 0;
+          }
+        },
+      )..onTapUp(),
+    );
+  }
+}

doc/flame/examples/lib/decorator_tint.dart

@@ -0,0 +1,36 @@
+import 'dart:ui';
+
+import 'package:doc_flame_examples/flower.dart';
+import 'package:flame/experimental.dart';
+import 'package:flame/game.dart';
+import 'package:flame/rendering.dart';
+
+class DecoratorTintGame extends FlameGame with HasTappableComponents {
+  @override
+  Future<void> onLoad() async {
+    var step = 0;
+    add(
+      Flower(
+        size: 100,
+        position: canvasSize / 2,
+        onTap: (flower) {
+          step++;
+          if (step == 1) {
+            flower.decorator = PaintDecorator.tint(const Color(0x88FF0000));
+          } else if (step == 2) {
+            flower.decorator = PaintDecorator.tint(const Color(0x8800FF00));
+          } else if (step == 3) {
+            flower.decorator = PaintDecorator.tint(const Color(0x88000088));
+          } else if (step == 4) {
+            flower.decorator = PaintDecorator.tint(const Color(0x66FFFFFF));
+          } else if (step == 5) {
+            flower.decorator = PaintDecorator.tint(const Color(0xAA000000));
+          } else {
+            flower.decorator = null;
+            step = 0;
+          }
+        },
+      )..onTapUp(),
+    );
+  }
+}

doc/flame/examples/lib/flower.dart

@@ -0,0 +1,53 @@
+import 'dart:math';
+import 'dart:ui';
+
+import 'package:flame/components.dart';
+import 'package:flame/experimental.dart';
+
+const tau = 2 * pi;
+
+class Flower extends PositionComponent with TapCallbacks, HasDecorator {
+  Flower({required double size, void Function(Flower)? onTap, super.position})
+      : _onTap = onTap,
+        super(size: Vector2.all(size), anchor: Anchor.center) {
+    final radius = size * 0.38;
+    _paths.add(_makePath(radius * 1.4, 6, -0.05, 0.8));
+    _paths.add(_makePath(radius, 6, 0.25, 1.5));
+    _paths.add(_makePath(radius * 0.8, 6, 0.3, 1.4));
+    _paths.add(_makePath(radius * 0.55, 6, 0.2, 1.5));
+    _paths.add(_makePath(radius * 0.1, 12, 0.1, 6));
+    _paints.add(Paint()..color = const Color(0xff255910));
+    _paints.add(Paint()..color = const Color(0xffee3f3f));
+    _paints.add(Paint()..color = const Color(0xffffbd66));
+    _paints.add(Paint()..color = const Color(0xfff6f370));
+    _paints.add(Paint()..color = const Color(0xfffffff0));
+  }
+
+  final List<Path> _paths = [];
+  final List<Paint> _paints = [];
+  final void Function(Flower)? _onTap;
+
+  Path _makePath(double radius, int n, double sharpness, double f) {
+    final radius2 = radius * f;
+    final p0 = Vector2(radius, 0)..rotate(0);
+    final path = Path()..moveTo(p0.x, p0.y);
+    for (var i = 0; i < n; i++) {
+      final p1 = Vector2(radius2, 0)..rotate(tau / n * (i + sharpness));
+      final p2 = Vector2(radius2, 0)..rotate(tau / n * (i + 1 - sharpness));
+      final p3 = Vector2(radius, 0)..rotate(tau / n * (i + 1));
+      path.cubicTo(p1.x, p1.y, p2.x, p2.y, p3.x, p3.y);
+    }
+    path.close();
+    return path.shift(Offset(width / 2, height / 2));
+  }
+
+  @override
+  void render(Canvas canvas) {
+    for (var i = 0; i < _paths.length; i++) {
+      canvas.drawPath(_paths[i], _paints[i]);
+    }
+  }
+
+  @override
+  void onTapUp([TapUpEvent? event]) => _onTap?.call(this);
+}

doc/flame/examples/lib/main.dart

@@ -1,5 +1,8 @@
 import 'dart:html'; // ignore: avoid_web_libraries_in_flutter
 
+import 'package:doc_flame_examples/decorator_blur.dart';
+import 'package:doc_flame_examples/decorator_grayscale.dart';
+import 'package:doc_flame_examples/decorator_tint.dart';
 import 'package:doc_flame_examples/drag_events.dart';
 import 'package:doc_flame_examples/tap_events.dart';
 import 'package:flame/game.dart';
@@ -18,6 +21,15 @@ void main() {
     case 'drag_events':
       game = DragEventsGame();
       break;
+    case 'decorator_blur':
+      game = DecoratorBlurGame();
+      break;
+    case 'decorator_grayscale':
+      game = DecoratorGrayscaleGame();
+      break;
+    case 'decorator_tinted':
+      game = DecoratorTintGame();
+      break;
   }
   if (game != null) {
     runApp(GameWidget(game: game));

doc/flame/rendering/decorators.md

@@ -0,0 +1,103 @@
+# Decorators
+
+**Decorators** are classes that can encapsulate certain visual effects and then apply those visual
+effects to a sequence of canvas drawing operations. Decorators are not [Component]s, but they can
+be applied to components either manually or via the [HasDecorator] mixin. Likewise, decorators are
+not [Effect]s, although they can be used to implement certain `Effect`s.
+
+There are a certain number of decorators available in Flame, and it is simple to add one's own if
+necessary. We are planning to add shader-based decorators once Flutter fully supports them on the
+web.
+
+
+## Flame built-in decorators
+
+### PaintDecorator.blur
+
+```{flutter-app}
+:sources: ../flame/examples
+:page: decorator_blur
+:show: widget code infobox
+:width: 180
+:height: 160
+```
+
+This decorator applies a Gaussian blur to the underlying component. The amount of blur can be
+different in the X and Y direction, though this is not very common.
+
+```dart
+final decorator = PaintDecorator.blur(3.0);
+```
+
+Possible uses:
+- soft shadows;
+- "out-of-focus" objects in the distance or very close to the camera;
+- motion blur effects;
+- deemphasize/obscure content when showing a popup dialog;
+- blurred vision when the character is drunk.
+
+
+### PaintDecorator.grayscale
+
+```{flutter-app}
+:sources: ../flame/examples
+:page: decorator_grayscale
+:show: widget infobox
+:width: 180
+:height: 160
+```
+
+This decorator converts the underlying image into the shades of grey, as if it was a
+black-and-white photograph. In addition, you can make the image semi-transparent to the desired
+level of `opacity`.
+
+```dart
+final decorator = PaintDecorator.grayscale(opacity: 0.5);
+```
+
+Possible uses:
+- apply to an NPC to turn them into stone, or into a ghost!
+- apply to a scene to indicate that it is a memory of the past;
+- black-and-white photos.
+
+
+### PaintDecorator.tint
+
+```{flutter-app}
+:sources: ../flame/examples
+:page: decorator_tint
+:show: widget infobox
+:width: 180
+:height: 160
+```
+
+This decorator *tints* the underlying image with the specified color, as if watching it through a
+colored glass. It is recommended that the `color` used by this decorator was semi-transparent, so
+that you can see the details of the image below.
+
+```dart
+final decorator = PaintDecorator.tint(const Color(0xAAFF0000);
+```
+
+Possible uses:
+- NPCs affected by certain types of magic;
+- items/characters in the shadows can be tinted black;
+- tint the scene red to show bloodlust, or that the character is low on health;
+- tint green to show that the character is poisoned or sick;
+- tint the scene deep blue during the night time;
+
+
+## Using decorators
+
+### HasDecorator mixin
+
+This `Component` mixin adds the `decorator` property, which is initially `null`. If you set this
+property to an actual `Decorator` object, then that decorator will apply its visual effect during
+the rendering of the component. In order to remove this visual effect, simply set the `decorator`
+property back to `null`.
+
+
+
+[Component]: ../../flame/components.md#component
+[Effect]: ../../flame/effects.md
+[HasDecorator]: #hasdecorator-mixin

doc/flame/rendering/rendering.md

@@ -8,5 +8,6 @@
     Text rendering                  <text.md>
     Colors and palette              <palette.md>
     Particles                       <particles.md>
+    Decorators                      <decorators.md>
     Layers                          <layers.md>
 ```

packages/flame/lib/components.dart

@@ -14,6 +14,7 @@ export 'src/components/mixins/component_viewport_margin.dart';
 export 'src/components/mixins/draggable.dart';
 export 'src/components/mixins/gesture_hitboxes.dart';
 export 'src/components/mixins/has_ancestor.dart';
+export 'src/components/mixins/has_decorator.dart' show HasDecorator;
 export 'src/components/mixins/has_game_ref.dart';
 export 'src/components/mixins/has_paint.dart';
 export 'src/components/mixins/hoverable.dart';

packages/flame/lib/rendering.dart

@@ -0,0 +1,2 @@
+export 'src/rendering/decorator.dart' show Decorator;
+export 'src/rendering/paint_decorator.dart' show PaintDecorator;

packages/flame/lib/src/components/mixins/has_decorator.dart

@@ -0,0 +1,27 @@
+import 'dart:ui';
+
+import 'package:flame/src/components/component.dart';
+import 'package:flame/src/rendering/decorator.dart';
+
+/// [HasDecorator] mixin adds a nullable [decorator] field to a Component. If
+/// this field is set, it will apply the visual effect encapsulated in this
+/// [Decorator] to the component. If the field is not set, then the component
+/// will be rendered normally.
+///
+/// Note that the decorator only affects visual rendering of a component, but
+/// not its perceived size or shape from the point of view of tap events.
+///
+/// See also:
+///  - [Decorator] class for the list of available decorators.
+mixin HasDecorator on Component {
+  Decorator? decorator;
+
+  @override
+  void renderTree(Canvas canvas) {
+    if (decorator == null) {
+      super.renderTree(canvas);
+    } else {
+      decorator!.apply(super.renderTree, canvas);
+    }
+  }
+}

packages/flame/lib/src/rendering/decorator.dart

@@ -0,0 +1,26 @@
+import 'dart:ui';
+
+import 'package:flame/src/rendering/paint_decorator.dart';
+
+/// [Decorator] is an abstract class that encapsulates a particular visual
+/// effect that should apply to drawing commands wrapped by this class.
+///
+/// The simplest way to apply a [Decorator] to a component is to override its
+/// `renderTree` method like this:
+/// ```dart
+/// @override
+/// void renderTree(Canvas canvas) {
+///   decorator.apply(super.renderTree, canvas);
+/// }
+/// ```
+///
+/// The following implementations are available:
+/// - [PaintDecorator]
+abstract class Decorator {
+  /// Applies visual effect while [draw]ing on the [canvas].
+  ///
+  /// A no-op decorator would simply call `draw(canvas)`. Any other non-trivial
+  /// decorator can transform the canvas before drawing, or perform any other
+  /// adjustment.
+  void apply(void Function(Canvas) draw, Canvas canvas);
+}

packages/flame/lib/src/rendering/paint_decorator.dart

@@ -0,0 +1,41 @@
+import 'dart:ui';
+
+import 'package:flame/src/rendering/decorator.dart';
+
+/// [PaintDecorator] applies a paint filter to a group of drawing operations.
+///
+/// Specifically, the following filters are available:
+/// - [PaintDecorator.blur] adds Gaussian blur to the image, as if your vision
+///   became blurry and out of focus;
+/// - [PaintDecorator.tint] tints the picture with the specified color, as if
+///   looking through a colored glass;
+/// - [PaintDecorator.grayscale] removes all color from the picture, as if it
+///   was a black-and-white photo.
+class PaintDecorator extends Decorator {
+  PaintDecorator.blur(double amount, [double? amountY]) {
+    addBlur(amount, amountY ?? amount);
+  }
+
+  PaintDecorator.tint(Color color) {
+    _paint.colorFilter = ColorFilter.mode(color, BlendMode.srcATop);
+  }
+
+  PaintDecorator.grayscale({double opacity = 1.0}) {
+    _paint.color = Color.fromARGB((255 * opacity).toInt(), 0, 0, 0);
+    _paint.blendMode = BlendMode.luminosity;
+  }
+
+  final _paint = Paint();
+
+  void addBlur(double amount, [double? amountY]) {
+    _paint.imageFilter =
+        ImageFilter.blur(sigmaX: amount, sigmaY: amountY ?? amount);
+  }
+
+  @override
+  void apply(void Function(Canvas) draw, Canvas canvas) {
+    canvas.saveLayer(null, _paint);
+    draw(canvas);
+    canvas.restore();
+  }
+}

packages/flame/test/components/mixins/has_decorator_test.dart

@@ -0,0 +1,43 @@
+import 'dart:ui';
+
+import 'package:flame/components.dart';
+import 'package:flame/rendering.dart';
+import 'package:flame_test/flame_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('HasDecorator', () {
+    testGolden(
+      'Component rendering with and without a Decorator',
+      (game) async {
+        await game.add(
+          _DecoratedComponent(
+            position: Vector2.all(25),
+            size: Vector2.all(40),
+          ),
+        );
+        await game.add(
+          _DecoratedComponent(
+            position: Vector2(75, 25),
+            size: Vector2.all(40),
+          )..decorator = (PaintDecorator.grayscale()..addBlur(2)),
+        );
+      },
+      size: Vector2(100, 50),
+      goldenFile: '../../_goldens/has_decorator_1.png',
+    );
+  });
+}
+
+class _DecoratedComponent extends PositionComponent with HasDecorator {
+  _DecoratedComponent({super.position, super.size})
+      : super(anchor: Anchor.center);
+
+  final paint = Paint()..color = const Color(0xff30ccd2);
+
+  @override
+  void render(Canvas canvas) {
+    final radius = size.x / 2;
+    canvas.drawCircle(Offset(radius, radius), radius, paint);
+  }
+}

packages/flame/test/rendering/paint_decorator_test.dart

@@ -0,0 +1,116 @@
+import 'dart:ui';
+
+import 'package:flame/components.dart';
+import 'package:flame/rendering.dart';
+import 'package:flame_test/flame_test.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../_resources/load_image.dart';
+
+void main() {
+  group('PaintDecorator', () {
+    testGolden(
+      'blur effect',
+      (game) async {
+        final image = await loadImage('flame.png');
+        game.addAll([
+          SpriteComponent(sprite: Sprite(image)),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.blur(0, 10),
+            position: Vector2(150, 0),
+          ),
+        ]);
+      },
+      size: Vector2(300, 220),
+      goldenFile: '../_goldens/paint_decorator_blur.png',
+    );
+
+    testGolden(
+      'grayscale effect',
+      (game) async {
+        final image = await loadImage('flame.png');
+        game.addAll([
+          SpriteComponent(sprite: Sprite(image)),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.grayscale(),
+            position: Vector2(150, 0),
+          ),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.grayscale(opacity: 0.5),
+            position: Vector2(300, 0),
+          ),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.grayscale(opacity: 0.25),
+            position: Vector2(450, 0),
+          ),
+        ]);
+      },
+      size: Vector2(600, 220),
+      goldenFile: '../_goldens/paint_decorator_grayscale.png',
+    );
+
+    testGolden(
+      'tint effect',
+      (game) async {
+        final image = await loadImage('zz_guitarre.png');
+        game.addAll([
+          SpriteComponent(sprite: Sprite(image)),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.tint(const Color(0x8800FF00)),
+            position: Vector2(100, 0),
+          ),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.tint(const Color(0x880000FF)),
+            position: Vector2(200, 0),
+          ),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.tint(const Color(0xAAFFFFFF)),
+            position: Vector2(300, 0),
+          ),
+        ]);
+      },
+      size: Vector2(400, 300),
+      goldenFile: '../_goldens/paint_decorator_tinted.png',
+    );
+
+    testGolden(
+      'grayscale/tinted with blur',
+      (game) async {
+        final image = await loadImage('zz_guitarre.png');
+        const color = Color(0x88EBFF7F);
+        game.addAll([
+          SpriteComponent(sprite: Sprite(image)),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.grayscale()..addBlur(3),
+            position: Vector2(100, 0),
+          ),
+          _DecoratedSprite(
+            sprite: Sprite(image),
+            decorator: PaintDecorator.tint(color)..addBlur(3),
+            position: Vector2(200, 0),
+          ),
+        ]);
+      },
+      size: Vector2(300, 300),
+      goldenFile: '../_goldens/paint_decorator_with_blur.png',
+    );
+  });
+}
+
+class _DecoratedSprite extends SpriteComponent {
+  _DecoratedSprite({super.sprite, super.position, required this.decorator});
+  final Decorator decorator;
+
+  @override
+  void renderTree(Canvas canvas) {
+    decorator.apply(super.renderTree, canvas);
+  }
+}