ImageDecoration.lerp (#130533)

This primarily implements DecorationImage.lerp().

It also makes some minor tweaks, the main one of which is defering to dart:ui for `clampDouble` instead of duplicating it in package:foundation.

Fixes https://github.com/flutter/flutter/issues/12452

analysis_options.yaml

@@ -50,7 +50,7 @@ linter:
     - avoid_field_initializers_in_const_classes
     # - avoid_final_parameters # incompatible with prefer_final_parameters
     - avoid_function_literals_in_foreach_calls
-    - avoid_implementing_value_types
+    # - avoid_implementing_value_types # see https://github.com/dart-lang/linter/issues/4558
     - avoid_init_to_null
     - avoid_js_rounded_ints
     # - avoid_multiple_declarations_per_line # seems to be a stylistic choice we don't subscribe to

packages/flutter/lib/foundation.dart

@@ -34,7 +34,6 @@ export 'src/foundation/diagnostics.dart';
 export 'src/foundation/isolates.dart';
 export 'src/foundation/key.dart';
 export 'src/foundation/licenses.dart';
-export 'src/foundation/math.dart';
 export 'src/foundation/memory_allocations.dart';
 export 'src/foundation/node.dart';
 export 'src/foundation/object.dart';

packages/flutter/lib/src/foundation/README.md

@@ -3,9 +3,9 @@ nothing but core Dart packages. They can't depend on `dart:ui`, they
 can't depend on any `package:`, and they can't depend on anything
 outside this directory.
 
-Currently they do depend on dart:ui, but only for `VoidCallback` (and
-maybe one day `lerpDouble`), which are all intended to be moved out
-of `dart:ui` and into `dart:core`.
+Currently they do depend on dart:ui, but only for `VoidCallback` and
+`clampDouble` (and maybe one day `lerpDouble`), which are all intended
+to be moved out of `dart:ui` and into `dart:core`.
 
 There is currently also an unfortunate dependency on the platform
 dispatcher logic (SingletonFlutterWindow, Brightness,
@@ -14,5 +14,4 @@ PlatformDispatcher, window), though that should probably move to the
 
 See also:
 
- * https://github.com/dart-lang/sdk/issues/27791 (`VoidCallback`)
- * https://github.com/dart-lang/sdk/issues/25217 (`hashValues`, `hashList`, and `lerpDouble`)
+ * https://github.com/dart-lang/sdk/issues/25217

packages/flutter/lib/src/foundation/binding.dart

@@ -22,7 +22,7 @@ import 'print.dart';
 import 'service_extensions.dart';
 import 'timeline.dart';
 
-export 'dart:ui' show PlatformDispatcher, SingletonFlutterWindow; // ignore: deprecated_member_use
+export 'dart:ui' show PlatformDispatcher, SingletonFlutterWindow, clampDouble; // ignore: deprecated_member_use
 
 export 'basic_types.dart' show AsyncCallback, AsyncValueGetter, AsyncValueSetter;
 

packages/flutter/lib/src/foundation/diagnostics.dart

@@ -3,13 +3,13 @@
 // found in the LICENSE file.
 
 import 'dart:math' as math;
+import 'dart:ui' show clampDouble;
 
 import 'package:meta/meta.dart';
 
 import 'assertions.dart';
 import 'constants.dart';
 import 'debug.dart';
-import 'math.dart' show clampDouble;
 import 'object.dart';
 
 // Examples can assume:

packages/flutter/lib/src/foundation/math.dart

-// Copyright 2014 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.
-
-/// Same as [num.clamp] but optimized for non-null [double].
-///
-/// This is faster because it avoids polymorphism, boxing, and special cases for
-/// floating point numbers.
-//
-// See also: //dev/benchmarks/microbenchmarks/lib/foundation/clamp.dart
-double clampDouble(double x, double min, double max) {
-  assert(min <= max && !max.isNaN && !min.isNaN);
-  if (x < min) {
-    return min;
-  }
-  if (x > max) {
-    return max;
-  }
-  if (x.isNaN) {
-    return max;
-  }
-  return x;
-}

packages/flutter/lib/src/material/dialog.dart

@@ -2,10 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
+import 'dart:ui' show clampDouble, lerpDouble;
 
 import 'package:flutter/cupertino.dart';
-import 'package:flutter/foundation.dart' show clampDouble;
 
 import 'color_scheme.dart';
 import 'colors.dart';

packages/flutter/lib/src/painting/box_decoration.dart

@@ -232,7 +232,7 @@ class BoxDecoration extends Decoration {
   BoxDecoration scale(double factor) {
     return BoxDecoration(
       color: Color.lerp(null, color, factor),
-      image: image, // TODO(ianh): fade the image from transparent
+      image: DecorationImage.lerp(null, image, factor),
       border: BoxBorder.lerp(null, border, factor),
       borderRadius: BorderRadiusGeometry.lerp(null, borderRadius, factor),
       boxShadow: BoxShadow.lerpList(null, boxShadow, factor),
@@ -307,7 +307,7 @@ class BoxDecoration extends Decoration {
     }
     return BoxDecoration(
       color: Color.lerp(a.color, b.color, t),
-      image: t < 0.5 ? a.image : b.image, // TODO(ianh): cross-fade the image
+      image: DecorationImage.lerp(a.image, b.image, t),
       border: BoxBorder.lerp(a.border, b.border, t),
       borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, b.borderRadius, t),
       boxShadow: BoxShadow.lerpList(a.boxShadow, b.boxShadow, t),

packages/flutter/lib/src/painting/shape_decoration.dart

@@ -237,7 +237,7 @@ class ShapeDecoration extends Decoration {
     return ShapeDecoration(
       color: Color.lerp(a?.color, b?.color, t),
       gradient: Gradient.lerp(a?.gradient, b?.gradient, t),
-      image: t < 0.5 ? a?.image : b?.image, // TODO(ianh): cross-fade the image
+      image: DecorationImage.lerp(a?.image, b?.image, t),
       shadows: BoxShadow.lerpList(a?.shadows, b?.shadows, t),
       shape: ShapeBorder.lerp(a?.shape, b?.shape, t)!,
     );