lib/web_ui/lib/src/engine/util.dart - external/github.com/flutter/engine - Git at Google

 // 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
 part of engine;

 /// Generic callback signature, used by [_futurize].
 typedef Callback<T> = void Function(T result);

 /// Signature for a method that receives a [_Callback].
 ///
 /// Return value should be null on success, and a string error message on
 /// failure.
 typedef Callbacker<T> = String Function(Callback<T> callback);

 /// Converts a method that receives a value-returning callback to a method that
 /// returns a Future.
 ///
 /// Return a [String] to cause an [Exception] to be synchronously thrown with
 /// that string as a message.
 ///
 /// If the callback is called with null, the future completes with an error.
 ///
 /// Example usage:
 ///
 /// ```dart
 /// typedef IntCallback = void Function(int result);
 ///
 /// String _doSomethingAndCallback(IntCallback callback) {
 ///   new Timer(new Duration(seconds: 1), () { callback(1); });
 /// }
 ///
 /// Future<int> doSomething() {
 ///   return _futurize(_doSomethingAndCallback);
 /// }
 /// ```
 Future<T> futurize<T>(Callbacker<T> callbacker) {
   final Completer<T> completer = Completer<T>.sync();
   final String error = callbacker((T t) {
     if (t == null) {
       completer.completeError(Exception('operation failed'));
     } else {
       completer.complete(t);
     }
   });
   if (error != null) {
     throw Exception(error);
   }
   return completer.future;
 }

 /// Converts [matrix] to CSS transform value.
 String matrix4ToCssTransform(Matrix4 matrix) {
   return float64ListToCssTransform(matrix.storage);
 }

 /// Applies a transform to the [element].
 ///
 /// See [float64ListToCssTransform] for details on how the CSS value is chosen.
 void setElementTransform(html.Element element, Float32List matrix4) {
   element.style
     ..transformOrigin = '0 0 0'
     ..transform = float64ListToCssTransform(matrix4);
 }

 /// Converts [matrix] to CSS transform value.
 ///
 /// To avoid blurry text on some screens this function uses a 2D CSS transform
 /// if it detects that [matrix] is a 2D transform. Otherwise, it uses a 3D CSS
 /// transform.
 ///
 /// See also:
 ///  * https://github.com/flutter/flutter/issues/32274
 ///  * https://bugs.chromium.org/p/chromium/issues/detail?id=1040222
 String float64ListToCssTransform(Float32List matrix) {
   assert(matrix.length == 16);
   final TransformKind transformKind = transformKindOf(matrix);
   if (transformKind == TransformKind.transform2d) {
     return float64ListToCssTransform2d(matrix);
   } else if (transformKind == TransformKind.complex) {
     return float64ListToCssTransform3d(matrix);
   } else {
     assert(transformKind == TransformKind.identity);
     return 'none';
   }
 }

 /// The kind of effect a transform matrix performs.
 enum TransformKind {
   /// No effect.
   ///
   /// We do not want to set any CSS properties in this case.
   identity,

   /// A transform that contains only 2d scale, rotation, and translation.
   ///
   /// We prefer to use "matrix" instead of "matrix3d" in this case.
   transform2d,

   /// All other kinds of transforms.
   ///
   /// In this case we will use "matrix3d".
   complex,
 }

 /// Detects the kind of transform the [matrix] performs.
 TransformKind transformKindOf(Float32List matrix) {
   assert(matrix.length == 16);
   final Float32List m = matrix;

   // If matrix contains scaling, rotation, z translation or
   // perspective transform, it is not considered simple.
   final bool isSimple2dTransform =
       m[15] == 1.0 &&  // start reading from the last element to eliminate range checks in subsequent reads.
       m[14] == 0.0 && // z translation is NOT simple
       // m[13] - y translation is simple
       // m[12] - x translation is simple
       m[11] == 0.0 &&
       m[10] == 1.0 &&
       m[9] == 0.0 &&
       m[8] == 0.0 &&
       m[7] == 0.0 &&
       m[6] == 0.0 &&
       // m[5] - scale y is simple
       // m[4] - 2D rotation is simple
       m[3] == 0.0 &&
       m[2] == 0.0;
       // m[1] - 2D rotation is simple
       // m[0] - scale x is simple

   if (!isSimple2dTransform) {
     return TransformKind.complex;
   }

   // From this point on we're sure the transform is 2D, but we don't know if
   // it's identity or not. To check, we need to look at the remaining elements
   // that were not checked above.
   final bool isIdentityTransform =
       m[0] == 1.0 &&
       m[1] == 0.0 &&
       m[4] == 0.0 &&
       m[5] == 1.0 &&
       m[12] == 0.0 &&
       m[13] == 0.0;

   if (isIdentityTransform) {
     return TransformKind.identity;
   } else {
     return TransformKind.transform2d;
   }
 }

 /// Returns `true` is the [matrix] describes an identity transformation.
 bool isIdentityFloat32ListTransform(Float32List matrix) {
   assert(matrix.length == 16);
   return transformKindOf(matrix) == TransformKind.identity;
 }

 /// Converts [matrix] to CSS transform 2D matrix value.
 ///
 /// The [matrix] must not be a [TransformKind.complex] transform, because CSS
 /// `matrix` can only express 2D transforms. [TransformKind.identity] is
 /// permitted. However, it is inefficient to construct a matrix for an identity
 /// transform. Consider removing the CSS `transform` property from elements
 /// that apply identity transform.
 String float64ListToCssTransform2d(Float32List matrix) {
   assert (transformKindOf(matrix) != TransformKind.complex);
   return 'matrix(${matrix[0]},${matrix[1]},${matrix[4]},${matrix[5]},${matrix[12]},${matrix[13]})';
 }

 /// Converts [matrix] to a 3D CSS transform value.
 String float64ListToCssTransform3d(Float32List matrix) {
   assert(matrix.length == 16);
   final Float32List m = matrix;
   if (m[0] == 1.0 &&
       m[1] == 0.0 &&
       m[2] == 0.0 &&
       m[3] == 0.0 &&
       m[4] == 0.0 &&
       m[5] == 1.0 &&
       m[6] == 0.0 &&
       m[7] == 0.0 &&
       m[8] == 0.0 &&
       m[9] == 0.0 &&
       m[10] == 1.0 &&
       m[11] == 0.0 &&
       // 12 can be anything
       // 13 can be anything
       m[14] == 0.0 &&
       m[15] == 1.0) {
     final double tx = m[12];
     final double ty = m[13];
     return 'translate3d(${tx}px, ${ty}px, 0px)';
   } else {
     return 'matrix3d(${m[0]},${m[1]},${m[2]},${m[3]},${m[4]},${m[5]},${m[6]},${m[7]},${m[8]},${m[9]},${m[10]},${m[11]},${m[12]},${m[13]},${m[14]},${m[15]})';
   }
 }

 bool get assertionsEnabled {
   bool k = false;
   assert(k = true);
   return k;
 }

 final Float32List _tempRectData = Float32List(4);

 /// Transforms a [ui.Rect] given the effective [transform].
 ///
 /// The resulting rect is aligned to the pixel grid, i.e. two of
 /// its sides are vertical and two are horizontal. In the presence of rotations
 /// the rectangle is inflated such that it fits the rotated rectangle.
 ui.Rect transformRect(Matrix4 transform, ui.Rect rect) {
   _tempRectData[0] = rect.left;
   _tempRectData[1] = rect.top;
   _tempRectData[2] = rect.right;
   _tempRectData[3] = rect.bottom;
   transformLTRB(transform, _tempRectData);
   return ui.Rect.fromLTRB(
     _tempRectData[0],
     _tempRectData[1],
     _tempRectData[2],
     _tempRectData[3],
   );
 }

 /// Temporary storage for intermediate data used by [transformLTRB].
 ///
 /// WARNING: do not use this outside [transformLTRB]. Sharing this variable in
 /// other contexts will lead to bugs.
 final Float32List _tempPointData = Float32List(16);
 final Matrix4 _tempPointMatrix = Matrix4.fromFloat32List(_tempPointData);

 /// Transforms a rectangle given the effective [transform].
 ///
 /// This is the same as [transformRect], except that the rect is specified
 /// in terms of left, top, right, and bottom edge offsets.
 void transformLTRB(Matrix4 transform, Float32List ltrb) {
   // Construct a matrix where each row represents a vector pointing at
   // one of the four corners of the (left, top, right, bottom) rectangle.
   // Using the row-major order allows us to multiply the matrix in-place
   // by the transposed current transformation matrix. The vector_math
   // library has a convenience function `multiplyTranspose` that performs
   // the multiplication without copying. This way we compute the positions
   // of all four points in a single matrix-by-matrix multiplication at the
   // cost of one `Matrix4` instance and one `Float32List` instance.
   //
   // The rejected alternative was to use `Vector3` for each point and
   // multiply by the current transform. However, that would cost us four
   // `Vector3` instances, four `Float32List` instances, and four
   // matrix-by-vector multiplications.
   //
   // `Float32List` initializes the array with zeros, so we do not have to
   // fill in every single element.

   // Row 0: top-left
   _tempPointData[0] = ltrb[0];
   _tempPointData[4] = ltrb[1];
   _tempPointData[8] = 0;
   _tempPointData[12] = 1;

   // Row 1: top-right
   _tempPointData[1] = ltrb[2];
   _tempPointData[5] = ltrb[1];
   _tempPointData[9] = 0;
   _tempPointData[13] = 1;

   // Row 2: bottom-left
   _tempPointData[2] = ltrb[0];
   _tempPointData[6] = ltrb[3];
   _tempPointData[10] = 0;
   _tempPointData[14] = 1;

   // Row 3: bottom-right
   _tempPointData[3] = ltrb[2];
   _tempPointData[7] = ltrb[3];
   _tempPointData[11] = 0;
   _tempPointData[15] = 1;

   _tempPointMatrix.multiplyTranspose(transform);

   ltrb[0] = math.min(math.min(math.min(_tempPointData[0], _tempPointData[1]), _tempPointData[2]), _tempPointData[3]);
   ltrb[1] = math.min(math.min(math.min(_tempPointData[4], _tempPointData[5]), _tempPointData[6]), _tempPointData[7]);
   ltrb[2] = math.max(math.max(math.max(_tempPointData[0], _tempPointData[1]), _tempPointData[2]), _tempPointData[3]);
   ltrb[3] = math.max(math.max(math.max(_tempPointData[4], _tempPointData[5]), _tempPointData[6]), _tempPointData[7]);
 }

 /// Returns true if [rect] contains every point that is also contained by the
 /// [other] rect.
 ///
 /// Points on the edges of both rectangles are also considered. For example,
 /// this returns true when the two rects are equal to each other.
 bool rectContainsOther(ui.Rect rect, ui.Rect other) {
   return rect.left <= other.left &&
       rect.top <= other.top &&
       rect.right >= other.right &&
       rect.bottom >= other.bottom;
 }

 /// Counter used for generating clip path id inside an svg <defs> tag.
 int _clipIdCounter = 0;

 /// Converts Path to svg element that contains a clip-path definition.
 ///
 /// Calling this method updates [_clipIdCounter]. The HTML id of the generated
 /// clip is set to "svgClip${_clipIdCounter}", e.g. "svgClip123".
 String _pathToSvgClipPath(ui.Path path,
     {double offsetX = 0,
     double offsetY = 0,
     double scaleX = 1.0,
     double scaleY = 1.0}) {
   _clipIdCounter += 1;
   final StringBuffer sb = StringBuffer();
   sb.write('<svg width="0" height="0" '
       'style="position:absolute">');
   sb.write('<defs>');

   final String clipId = 'svgClip$_clipIdCounter';
   sb.write('<clipPath id=$clipId clipPathUnits="objectBoundingBox">');

   sb.write('<path transform="scale($scaleX, $scaleY)" fill="#FFFFFF" d="');
   pathToSvg(path, sb, offsetX: offsetX, offsetY: offsetY);
   sb.write('"></path></clipPath></defs></svg');
   return sb.toString();
 }

 /// Converts color to a css compatible attribute value.
 String colorToCssString(ui.Color color) {
   if (color == null) {
     return null;
   }
   final int value = color.value;
   if ((0xff000000 & value) == 0xff000000) {
     final String hexValue = (value & 0xFFFFFF).toRadixString(16);
     final int hexValueLength = hexValue.length;
     switch (hexValueLength) {
       case 1:
         return '#00000$hexValue';
       case 2:
         return '#0000$hexValue';
       case 3:
         return '#000$hexValue';
       case 4:
         return '#00$hexValue';
       case 5:
         return '#0$hexValue';
       default:
         return '#$hexValue';
     }
   } else {
     final double alpha = ((value >> 24) & 0xFF) / 255.0;
     final StringBuffer sb = StringBuffer();
     sb.write('rgba(');
     sb.write(((value >> 16) & 0xFF).toString());
     sb.write(',');
     sb.write(((value >> 8) & 0xFF).toString());
     sb.write(',');
     sb.write((value & 0xFF).toString());
     sb.write(',');
     sb.write(alpha.toString());
     sb.write(')');
     return sb.toString();
   }
 }

 /// Converts color components to a CSS compatible attribute value.
 String colorComponentsToCssString(int r, int g, int b, int a) {
   if (a == 255) {
     return 'rgb($r,$g,$b)';
   } else {
     final double alphaRatio = a / 255;
     return 'rgba($r,$g,$b,${alphaRatio.toStringAsFixed(2)})';
   }
 }

 /// Determines if the (dynamic) exception passed in is a NS_ERROR_FAILURE
 /// (from Firefox).
 ///
 /// NS_ERROR_FAILURE (0x80004005) is the most general of all the (Firefox)
 /// errors and occurs for all errors for which a more specific error code does
 /// not apply. (https://developer.mozilla.org/en-US/docs/Mozilla/Errors)
 ///
 /// Other browsers do not throw this exception.
 ///
 /// In Flutter, this exception happens when we try to perform some operations on
 /// a Canvas when the application is rendered in a display:none iframe.
 ///
 /// We need this in [BitmapCanvas] and [RecordingCanvas] to swallow this
 /// Firefox exception without interfering with others (potentially useful
 /// for the programmer).
 bool _isNsErrorFailureException(dynamic e) {
   return js_util.getProperty(e, 'name') == 'NS_ERROR_FAILURE';
 }

 /// From: https://developer.mozilla.org/en-US/docs/Web/CSS/font-family#Syntax
 ///
 /// Generic font families are a fallback mechanism, a means of preserving some
 /// of the style sheet author's intent when none of the specified fonts are
 /// available. Generic family names are keywords and must not be quoted. A
 /// generic font family should be the last item in the list of font family
 /// names.
 const Set<String> _genericFontFamilies = <String>{
   'serif',
   'sans-serif',
   'monospace',
   'cursive',
   'fantasy',
   'system-ui',
   'math',
   'emoji',
   'fangsong',
 };

 /// A default fallback font family in case an unloaded font has been requested.
 ///
 /// For iOS, default to Helvetica, where it should be available, otherwise
 /// default to Arial.
 final String _fallbackFontFamily =
     operatingSystem == OperatingSystem.iOs ? 'Helvetica' : 'Arial';

 /// Create a font-family string appropriate for CSS.
 ///
 /// If the given [fontFamily] is a generic font-family, then just return it.
 /// Otherwise, wrap the family name in quotes and add a fallback font family.
 String canonicalizeFontFamily(String fontFamily) {
   if (_genericFontFamilies.contains(fontFamily)) {
     return fontFamily;
   }
   return '"$fontFamily", $_fallbackFontFamily, sans-serif';
 }

 /// Converts a list of [Offset] to a typed array of floats.
 Float32List offsetListToFloat32List(List<ui.Offset> offsetList) {
   if (offsetList == null) {
     return null;
   }
   final int length = offsetList.length;
   final floatList = Float32List(length * 2);
   for (int i = 0, destIndex = 0; i < length; i++, destIndex += 2) {
     floatList[destIndex] = offsetList[i].dx;
     floatList[destIndex + 1] = offsetList[i].dy;
   }
   return floatList;
 }

 /// Apply this function to container elements in the HTML render tree (this is
 /// not relevant to semantics tree).
 ///
 /// On WebKit browsers this will apply `z-order: 0` to ensure that clips are
 /// applied correctly. Otherwise, the browser will refuse to clip its contents.
 ///
 /// Other possible fixes that were rejected:
 ///
 /// * Use 3D transform instead of 2D: this does not work because it causes text
 ///   blurriness: https://github.com/flutter/flutter/issues/32274
 void applyWebkitClipFix(html.Element containerElement) {
   if (browserEngine == BrowserEngine.webkit) {
     containerElement.style.zIndex = '0';
   }
 }

 final ByteData _fontChangeMessage = JSONMessageCodec().encodeMessage(<String, dynamic>{'type': 'fontsChange'});

 // Font load callbacks will typically arrive in sequence, we want to prevent
 // sendFontChangeMessage of causing multiple synchronous rebuilds.
 // This flag ensures we properly schedule a single call to framework.
 bool _fontChangeScheduled = false;

 FutureOr<void> sendFontChangeMessage() async {
   if (window._onPlatformMessage != null)
     if (!_fontChangeScheduled) {
       _fontChangeScheduled = true;
       // Batch updates into next animationframe.
       html.window.requestAnimationFrame((num _) {
         _fontChangeScheduled = false;
         window.invokeOnPlatformMessage(
           'flutter/system',
           _fontChangeMessage,
               (_) {},
         );
       });
     }
 }

 // Stores matrix in a form that allows zero allocation transforms.
 class _FastMatrix64 {
   final Float64List matrix;
   double transformedX = 0, transformedY = 0;
   _FastMatrix64(this.matrix);

   void transform(double x, double y) {
     transformedX = matrix[12] + (matrix[0] * x) + (matrix[4] * y);
     transformedY = matrix[13] + (matrix[1] * x) + (matrix[5] * y);
   }
 }
	// 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
	part of engine;

	/// Generic callback signature, used by [_futurize].
	typedef Callback<T> = void Function(T result);

	/// Signature for a method that receives a [_Callback].
	///
	/// Return value should be null on success, and a string error message on
	/// failure.
	typedef Callbacker<T> = String Function(Callback<T> callback);

	/// Converts a method that receives a value-returning callback to a method that
	/// returns a Future.
	///
	/// Return a [String] to cause an [Exception] to be synchronously thrown with
	/// that string as a message.
	///
	/// If the callback is called with null, the future completes with an error.
	///
	/// Example usage:
	///
	/// ```dart
	/// typedef IntCallback = void Function(int result);
	///
	/// String _doSomethingAndCallback(IntCallback callback) {
	/// new Timer(new Duration(seconds: 1), () { callback(1); });
	/// }
	///
	/// Future<int> doSomething() {
	/// return _futurize(_doSomethingAndCallback);
	/// }
	/// ```
	Future<T> futurize<T>(Callbacker<T> callbacker) {
	final Completer<T> completer = Completer<T>.sync();
	final String error = callbacker((T t) {
	if (t == null) {
	completer.completeError(Exception('operation failed'));
	} else {
	completer.complete(t);
	}
	});
	if (error != null) {
	throw Exception(error);
	}
	return completer.future;
	}

	/// Converts [matrix] to CSS transform value.
	String matrix4ToCssTransform(Matrix4 matrix) {
	return float64ListToCssTransform(matrix.storage);
	}

	/// Applies a transform to the [element].
	///
	/// See [float64ListToCssTransform] for details on how the CSS value is chosen.
	void setElementTransform(html.Element element, Float32List matrix4) {
	element.style
	..transformOrigin = '0 0 0'
	..transform = float64ListToCssTransform(matrix4);
	}

	/// Converts [matrix] to CSS transform value.
	///
	/// To avoid blurry text on some screens this function uses a 2D CSS transform
	/// if it detects that [matrix] is a 2D transform. Otherwise, it uses a 3D CSS
	/// transform.
	///
	/// See also:
	/// * https://github.com/flutter/flutter/issues/32274
	/// * https://bugs.chromium.org/p/chromium/issues/detail?id=1040222
	String float64ListToCssTransform(Float32List matrix) {
	assert(matrix.length == 16);
	final TransformKind transformKind = transformKindOf(matrix);
	if (transformKind == TransformKind.transform2d) {
	return float64ListToCssTransform2d(matrix);
	} else if (transformKind == TransformKind.complex) {
	return float64ListToCssTransform3d(matrix);
	} else {
	assert(transformKind == TransformKind.identity);
	return 'none';
	}
	}

	/// The kind of effect a transform matrix performs.
	enum TransformKind {
	/// No effect.
	///
	/// We do not want to set any CSS properties in this case.
	identity,

	/// A transform that contains only 2d scale, rotation, and translation.
	///
	/// We prefer to use "matrix" instead of "matrix3d" in this case.
	transform2d,

	/// All other kinds of transforms.
	///
	/// In this case we will use "matrix3d".
	complex,
	}

	/// Detects the kind of transform the [matrix] performs.
	TransformKind transformKindOf(Float32List matrix) {
	assert(matrix.length == 16);
	final Float32List m = matrix;

	// If matrix contains scaling, rotation, z translation or
	// perspective transform, it is not considered simple.
	final bool isSimple2dTransform =
	m[15] == 1.0 && // start reading from the last element to eliminate range checks in subsequent reads.
	m[14] == 0.0 && // z translation is NOT simple
	// m[13] - y translation is simple
	// m[12] - x translation is simple
	m[11] == 0.0 &&
	m[10] == 1.0 &&
	m[9] == 0.0 &&
	m[8] == 0.0 &&
	m[7] == 0.0 &&
	m[6] == 0.0 &&
	// m[5] - scale y is simple
	// m[4] - 2D rotation is simple
	m[3] == 0.0 &&
	m[2] == 0.0;
	// m[1] - 2D rotation is simple
	// m[0] - scale x is simple

	if (!isSimple2dTransform) {
	return TransformKind.complex;
	}

	// From this point on we're sure the transform is 2D, but we don't know if
	// it's identity or not. To check, we need to look at the remaining elements
	// that were not checked above.
	final bool isIdentityTransform =
	m[0] == 1.0 &&
	m[1] == 0.0 &&
	m[4] == 0.0 &&
	m[5] == 1.0 &&
	m[12] == 0.0 &&
	m[13] == 0.0;

	if (isIdentityTransform) {
	return TransformKind.identity;
	} else {
	return TransformKind.transform2d;
	}
	}

	/// Returns `true` is the [matrix] describes an identity transformation.
	bool isIdentityFloat32ListTransform(Float32List matrix) {
	assert(matrix.length == 16);
	return transformKindOf(matrix) == TransformKind.identity;
	}

	/// Converts [matrix] to CSS transform 2D matrix value.
	///
	/// The [matrix] must not be a [TransformKind.complex] transform, because CSS
	/// `matrix` can only express 2D transforms. [TransformKind.identity] is
	/// permitted. However, it is inefficient to construct a matrix for an identity
	/// transform. Consider removing the CSS `transform` property from elements
	/// that apply identity transform.
	String float64ListToCssTransform2d(Float32List matrix) {
	assert (transformKindOf(matrix) != TransformKind.complex);
	return 'matrix(${matrix[0]},${matrix[1]},${matrix[4]},${matrix[5]},${matrix[12]},${matrix[13]})';
	}

	/// Converts [matrix] to a 3D CSS transform value.
	String float64ListToCssTransform3d(Float32List matrix) {
	assert(matrix.length == 16);
	final Float32List m = matrix;
	if (m[0] == 1.0 &&
	m[1] == 0.0 &&
	m[2] == 0.0 &&
	m[3] == 0.0 &&
	m[4] == 0.0 &&
	m[5] == 1.0 &&
	m[6] == 0.0 &&
	m[7] == 0.0 &&
	m[8] == 0.0 &&
	m[9] == 0.0 &&
	m[10] == 1.0 &&
	m[11] == 0.0 &&
	// 12 can be anything
	// 13 can be anything
	m[14] == 0.0 &&
	m[15] == 1.0) {
	final double tx = m[12];
	final double ty = m[13];
	return 'translate3d(${tx}px, ${ty}px, 0px)';
	} else {
	return 'matrix3d(${m[0]},${m[1]},${m[2]},${m[3]},${m[4]},${m[5]},${m[6]},${m[7]},${m[8]},${m[9]},${m[10]},${m[11]},${m[12]},${m[13]},${m[14]},${m[15]})';
	}
	}

	bool get assertionsEnabled {
	bool k = false;
	assert(k = true);
	return k;
	}

	final Float32List _tempRectData = Float32List(4);

	/// Transforms a [ui.Rect] given the effective [transform].
	///
	/// The resulting rect is aligned to the pixel grid, i.e. two of
	/// its sides are vertical and two are horizontal. In the presence of rotations
	/// the rectangle is inflated such that it fits the rotated rectangle.
	ui.Rect transformRect(Matrix4 transform, ui.Rect rect) {
	_tempRectData[0] = rect.left;
	_tempRectData[1] = rect.top;
	_tempRectData[2] = rect.right;
	_tempRectData[3] = rect.bottom;
	transformLTRB(transform, _tempRectData);
	return ui.Rect.fromLTRB(
	_tempRectData[0],
	_tempRectData[1],
	_tempRectData[2],
	_tempRectData[3],
	);
	}

	/// Temporary storage for intermediate data used by [transformLTRB].
	///
	/// WARNING: do not use this outside [transformLTRB]. Sharing this variable in
	/// other contexts will lead to bugs.
	final Float32List _tempPointData = Float32List(16);
	final Matrix4 _tempPointMatrix = Matrix4.fromFloat32List(_tempPointData);

	/// Transforms a rectangle given the effective [transform].
	///
	/// This is the same as [transformRect], except that the rect is specified
	/// in terms of left, top, right, and bottom edge offsets.
	void transformLTRB(Matrix4 transform, Float32List ltrb) {
	// Construct a matrix where each row represents a vector pointing at
	// one of the four corners of the (left, top, right, bottom) rectangle.
	// Using the row-major order allows us to multiply the matrix in-place
	// by the transposed current transformation matrix. The vector_math
	// library has a convenience function `multiplyTranspose` that performs
	// the multiplication without copying. This way we compute the positions
	// of all four points in a single matrix-by-matrix multiplication at the
	// cost of one `Matrix4` instance and one `Float32List` instance.
	//
	// The rejected alternative was to use `Vector3` for each point and
	// multiply by the current transform. However, that would cost us four
	// `Vector3` instances, four `Float32List` instances, and four
	// matrix-by-vector multiplications.
	//
	// `Float32List` initializes the array with zeros, so we do not have to
	// fill in every single element.

	// Row 0: top-left
	_tempPointData[0] = ltrb[0];
	_tempPointData[4] = ltrb[1];
	_tempPointData[8] = 0;
	_tempPointData[12] = 1;

	// Row 1: top-right
	_tempPointData[1] = ltrb[2];
	_tempPointData[5] = ltrb[1];
	_tempPointData[9] = 0;
	_tempPointData[13] = 1;

	// Row 2: bottom-left
	_tempPointData[2] = ltrb[0];
	_tempPointData[6] = ltrb[3];
	_tempPointData[10] = 0;
	_tempPointData[14] = 1;

	// Row 3: bottom-right
	_tempPointData[3] = ltrb[2];
	_tempPointData[7] = ltrb[3];
	_tempPointData[11] = 0;
	_tempPointData[15] = 1;

	_tempPointMatrix.multiplyTranspose(transform);

	ltrb[0] = math.min(math.min(math.min(_tempPointData[0], _tempPointData[1]), _tempPointData[2]), _tempPointData[3]);
	ltrb[1] = math.min(math.min(math.min(_tempPointData[4], _tempPointData[5]), _tempPointData[6]), _tempPointData[7]);
	ltrb[2] = math.max(math.max(math.max(_tempPointData[0], _tempPointData[1]), _tempPointData[2]), _tempPointData[3]);
	ltrb[3] = math.max(math.max(math.max(_tempPointData[4], _tempPointData[5]), _tempPointData[6]), _tempPointData[7]);
	}

	/// Returns true if [rect] contains every point that is also contained by the
	/// [other] rect.
	///
	/// Points on the edges of both rectangles are also considered. For example,
	/// this returns true when the two rects are equal to each other.
	bool rectContainsOther(ui.Rect rect, ui.Rect other) {
	return rect.left <= other.left &&
	rect.top <= other.top &&
	rect.right >= other.right &&
	rect.bottom >= other.bottom;
	}

	/// Counter used for generating clip path id inside an svg <defs> tag.
	int _clipIdCounter = 0;

	/// Converts Path to svg element that contains a clip-path definition.
	///
	/// Calling this method updates [_clipIdCounter]. The HTML id of the generated
	/// clip is set to "svgClip${_clipIdCounter}", e.g. "svgClip123".
	String _pathToSvgClipPath(ui.Path path,
	{double offsetX = 0,
	double offsetY = 0,
	double scaleX = 1.0,
	double scaleY = 1.0}) {
	_clipIdCounter += 1;
	final StringBuffer sb = StringBuffer();
	sb.write('<svg width="0" height="0" '
	'style="position:absolute">');
	sb.write('<defs>');

	final String clipId = 'svgClip$_clipIdCounter';
	sb.write('<clipPath id=$clipId clipPathUnits="objectBoundingBox">');

	sb.write('<path transform="scale($scaleX, $scaleY)" fill="#FFFFFF" d="');
	pathToSvg(path, sb, offsetX: offsetX, offsetY: offsetY);
	sb.write('"></path></clipPath></defs></svg');
	return sb.toString();
	}

	/// Converts color to a css compatible attribute value.
	String colorToCssString(ui.Color color) {
	if (color == null) {
	return null;
	}
	final int value = color.value;
	if ((0xff000000 & value) == 0xff000000) {
	final String hexValue = (value & 0xFFFFFF).toRadixString(16);
	final int hexValueLength = hexValue.length;
	switch (hexValueLength) {
	case 1:
	return '#00000$hexValue';
	case 2:
	return '#0000$hexValue';
	case 3:
	return '#000$hexValue';
	case 4:
	return '#00$hexValue';
	case 5:
	return '#0$hexValue';
	default:
	return '#$hexValue';
	}
	} else {
	final double alpha = ((value >> 24) & 0xFF) / 255.0;
	final StringBuffer sb = StringBuffer();
	sb.write('rgba(');
	sb.write(((value >> 16) & 0xFF).toString());
	sb.write(',');
	sb.write(((value >> 8) & 0xFF).toString());
	sb.write(',');
	sb.write((value & 0xFF).toString());
	sb.write(',');
	sb.write(alpha.toString());
	sb.write(')');
	return sb.toString();
	}
	}

	/// Converts color components to a CSS compatible attribute value.
	String colorComponentsToCssString(int r, int g, int b, int a) {
	if (a == 255) {
	return 'rgb($r,$g,$b)';
	} else {
	final double alphaRatio = a / 255;
	return 'rgba($r,$g,$b,${alphaRatio.toStringAsFixed(2)})';
	}
	}

	/// Determines if the (dynamic) exception passed in is a NS_ERROR_FAILURE
	/// (from Firefox).
	///
	/// NS_ERROR_FAILURE (0x80004005) is the most general of all the (Firefox)
	/// errors and occurs for all errors for which a more specific error code does
	/// not apply. (https://developer.mozilla.org/en-US/docs/Mozilla/Errors)
	///
	/// Other browsers do not throw this exception.
	///
	/// In Flutter, this exception happens when we try to perform some operations on
	/// a Canvas when the application is rendered in a display:none iframe.
	///
	/// We need this in [BitmapCanvas] and [RecordingCanvas] to swallow this
	/// Firefox exception without interfering with others (potentially useful
	/// for the programmer).
	bool _isNsErrorFailureException(dynamic e) {
	return js_util.getProperty(e, 'name') == 'NS_ERROR_FAILURE';
	}

	/// From: https://developer.mozilla.org/en-US/docs/Web/CSS/font-family#Syntax
	///
	/// Generic font families are a fallback mechanism, a means of preserving some
	/// of the style sheet author's intent when none of the specified fonts are
	/// available. Generic family names are keywords and must not be quoted. A
	/// generic font family should be the last item in the list of font family
	/// names.
	const Set<String> _genericFontFamilies = <String>{
	'serif',
	'sans-serif',
	'monospace',
	'cursive',
	'fantasy',
	'system-ui',
	'math',
	'emoji',
	'fangsong',
	};

	/// A default fallback font family in case an unloaded font has been requested.
	///
	/// For iOS, default to Helvetica, where it should be available, otherwise
	/// default to Arial.
	final String _fallbackFontFamily =
	operatingSystem == OperatingSystem.iOs ? 'Helvetica' : 'Arial';

	/// Create a font-family string appropriate for CSS.
	///
	/// If the given [fontFamily] is a generic font-family, then just return it.
	/// Otherwise, wrap the family name in quotes and add a fallback font family.
	String canonicalizeFontFamily(String fontFamily) {
	if (_genericFontFamilies.contains(fontFamily)) {
	return fontFamily;
	}
	return '"$fontFamily", $_fallbackFontFamily, sans-serif';
	}

	/// Converts a list of [Offset] to a typed array of floats.
	Float32List offsetListToFloat32List(List<ui.Offset> offsetList) {
	if (offsetList == null) {
	return null;
	}
	final int length = offsetList.length;
	final floatList = Float32List(length * 2);
	for (int i = 0, destIndex = 0; i < length; i++, destIndex += 2) {
	floatList[destIndex] = offsetList[i].dx;
	floatList[destIndex + 1] = offsetList[i].dy;
	}
	return floatList;
	}

	/// Apply this function to container elements in the HTML render tree (this is
	/// not relevant to semantics tree).
	///
	/// On WebKit browsers this will apply `z-order: 0` to ensure that clips are
	/// applied correctly. Otherwise, the browser will refuse to clip its contents.
	///
	/// Other possible fixes that were rejected:
	///
	/// * Use 3D transform instead of 2D: this does not work because it causes text
	/// blurriness: https://github.com/flutter/flutter/issues/32274
	void applyWebkitClipFix(html.Element containerElement) {
	if (browserEngine == BrowserEngine.webkit) {
	containerElement.style.zIndex = '0';
	}
	}

	final ByteData _fontChangeMessage = JSONMessageCodec().encodeMessage(<String, dynamic>{'type': 'fontsChange'});

	// Font load callbacks will typically arrive in sequence, we want to prevent
	// sendFontChangeMessage of causing multiple synchronous rebuilds.
	// This flag ensures we properly schedule a single call to framework.
	bool _fontChangeScheduled = false;

	FutureOr<void> sendFontChangeMessage() async {
	if (window._onPlatformMessage != null)
	if (!_fontChangeScheduled) {
	_fontChangeScheduled = true;
	// Batch updates into next animationframe.
	html.window.requestAnimationFrame((num _) {
	_fontChangeScheduled = false;
	window.invokeOnPlatformMessage(
	'flutter/system',
	_fontChangeMessage,
	(_) {},
	);
	});
	}
	}

	// Stores matrix in a form that allows zero allocation transforms.
	class _FastMatrix64 {
	final Float64List matrix;
	double transformedX = 0, transformedY = 0;
	_FastMatrix64(this.matrix);

	void transform(double x, double y) {
	transformedX = matrix[12] + (matrix[0] * x) + (matrix[4] * y);
	transformedY = matrix[13] + (matrix[1] * x) + (matrix[5] * y);
	}
	}