// Copyright 2015 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'dart:math' as math; import 'dart:ui' as ui show Gradient, lerpDouble; import 'package:flutter/foundation.dart'; import 'alignment.dart'; import 'basic_types.dart'; class _ColorsAndStops { _ColorsAndStops(this.colors, this.stops); final List<Color> colors; final List<double> stops; } _ColorsAndStops _interpolateColorsAndStops(List<Color> aColors, List<double> aStops, List<Color> bColors, List<double> bStops, double t) { assert(aColors.length == bColors.length, 'Cannot interpolate between two gradients with a different number of colors.'); // TODO(ianh): remove limitation assert((aStops == null && aColors.length == 2) || (aStops != null && aStops.length == aColors.length)); assert((bStops == null && bColors.length == 2) || (bStops != null && bStops.length == bColors.length)); final List<Color> interpolatedColors = <Color>[]; for (int i = 0; i < aColors.length; i += 1) interpolatedColors.add(Color.lerp(aColors[i], bColors[i], t)); List<double> interpolatedStops; if (aStops != null || bStops != null) { aStops ??= const <double>[0.0, 1.0]; bStops ??= const <double>[0.0, 1.0]; assert(aStops.length == bStops.length); for (int i = 0; i < aStops.length; i += 1) interpolatedStops.add(ui.lerpDouble(aStops[i], bStops[i], t).clamp(0.0, 1.0)); } return new _ColorsAndStops(interpolatedColors, interpolatedStops); } /// A 2D gradient. /// /// This is an interface that allows [LinearGradient] and [RadialGradient] /// classes to be used interchangeably in [BoxDecoration]s. /// /// See also: /// /// * [dart:ui.Gradient], the class in the [dart:ui] library that is /// encapsulated by this class and its subclasses. @immutable abstract class Gradient { /// Initialize the gradient's colors and stops. /// /// The [colors] argument must not be null, and must have at least two colors /// (the length is not verified until the [createShader] method is called). /// /// If specified, the [stops] argument must have the same number of entries as /// [colors] (this is also not verified until the [createShader] method is /// called). const Gradient({ @required this.colors, this.stops, }) : assert(colors != null); /// The colors the gradient should obtain at each of the stops. /// /// If [stops] is non-null, this list must have the same length as [stops]. /// /// This list must have at least two colors in it (otherwise, it's not a /// gradient!). final List<Color> colors; /// A list of values from 0.0 to 1.0 that denote fractions along the gradient. /// /// If non-null, this list must have the same length as [colors]. /// /// If the first value is not 0.0, then a stop with position 0.0 and a color /// equal to the first color in [colors] is implied. /// /// If the last value is not 1.0, then a stop with position 1.0 and a color /// equal to the last color in [colors] is implied. /// /// The values in the [stops] list must be in ascending order. If a value in /// the [stops] list is less than an earlier value in the list, then its value /// is assumed to equal the previous value. /// /// If stops is null, then a set of uniformly distributed stops is implied, /// with the first stop at 0.0 and the last stop at 1.0. final List<double> stops; List<double> _impliedStops() { if (stops != null) return stops; if (colors.length == 2) return null; assert(colors.length >= 2, 'colors list must have at least two colors'); final double separation = 1.0 / (colors.length - 1); return new List<double>.generate( colors.length, (int index) => index * separation, growable: false, ); } /// Creates a [Shader] for this gradient to fill the given rect. /// /// If the gradient's configuration is text-direction-dependent, for example /// it uses [AlignmentDirectional] objects instead of [Alignment] /// objects, then the `textDirection` argument must not be null. Shader createShader(Rect rect, { TextDirection textDirection }); /// Returns a new gradient with its properties scaled by the given factor. /// /// A factor of 0.0 (or less) should result in a variant of the gradient that /// is invisible; any two factors epsilon apart should be unnoticeably /// different from each other at first glance. From this it follows that /// scaling a gradient with values from 1.0 to 0.0 over time should cause the /// gradient to smoothly disappear. /// /// Typically this is the same as interpolating from null (with [lerp]). Gradient scale(double factor); /// Linearly interpolates from another [Gradient] to `this`. /// /// When implementing this method in subclasses, return null if this class /// cannot interpolate from `a`. In that case, [lerp] will try `a`'s [lerpTo] /// method instead. /// /// If `a` is null, this must not return null. The base class implements this /// by deferring to [scale]. /// /// The `t` argument represents position on the timeline, with 0.0 meaning /// that the interpolation has not started, returning `a` (or something /// equivalent to `a`), 1.0 meaning that the interpolation has finished, /// returning `this` (or something equivalent to `this`), and values in /// between meaning that the interpolation is at the relevant point on the /// timeline between `a` and `this`. The interpolation can be extrapolated /// beyond 0.0 and 1.0, so negative values and values greater than 1.0 are /// valid (and can easily be generated by curves such as /// [Curves.elasticInOut]). /// /// Values for `t` are usually obtained from an [Animation<double>], such as /// an [AnimationController]. /// /// Instead of calling this directly, use [Gradient.lerp]. @protected Gradient lerpFrom(Gradient a, double t) { if (a == null) return scale(t); return null; } /// Linearly interpolates from `this` to another [Gradient]. /// /// This is called if `b`'s [lerpTo] did not know how to handle this class. /// /// When implementing this method in subclasses, return null if this class /// cannot interpolate from `b`. In that case, [lerp] will apply a default /// behavior instead. /// /// If `b` is null, this must not return null. The base class implements this /// by deferring to [scale]. /// /// The `t` argument represents position on the timeline, with 0.0 meaning /// that the interpolation has not started, returning `this` (or something /// equivalent to `this`), 1.0 meaning that the interpolation has finished, /// returning `b` (or something equivalent to `b`), and values in between /// meaning that the interpolation is at the relevant point on the timeline /// between `this` and `b`. The interpolation can be extrapolated beyond 0.0 /// and 1.0, so negative values and values greater than 1.0 are valid (and can /// easily be generated by curves such as [Curves.elasticInOut]). /// /// Values for `t` are usually obtained from an [Animation<double>], such as /// an [AnimationController]. /// /// Instead of calling this directly, use [Gradient.lerp]. @protected Gradient lerpTo(Gradient b, double t) { if (b == null) return scale(1.0 - t); return null; } /// Linearly interpolates between two [Gradient]s. /// /// This defers to `b`'s [lerpTo] function if `b` is not null. If `b` is /// null or if its [lerpTo] returns null, it uses `a`'s [lerpFrom] /// function instead. If both return null, it returns `a` before `t == 0.5` /// and `b` after `t == 0.5`. /// /// The `t` argument represents position on the timeline, with 0.0 meaning /// that the interpolation has not started, returning `a` (or something /// equivalent to `a`), 1.0 meaning that the interpolation has finished, /// returning `b` (or something equivalent to `b`), and values in between /// meaning that the interpolation is at the relevant point on the timeline /// between `a` and `b`. The interpolation can be extrapolated beyond 0.0 and /// 1.0, so negative values and values greater than 1.0 are valid (and can /// easily be generated by curves such as [Curves.elasticInOut]). /// /// Values for `t` are usually obtained from an [Animation<double>], such as /// an [AnimationController]. static Gradient lerp(Gradient a, Gradient b, double t) { assert(t != null); Gradient result; if (b != null) result = b.lerpFrom(a, t); // if a is null, this must return non-null if (result == null && a != null) result = a.lerpTo(b, t); // if b is null, this must return non-null if (result != null) return result; if (a == null && b == null) return null; assert(a != null && b != null); return t < 0.5 ? a.scale(1.0 - (t * 2.0)) : b.scale((t - 0.5) * 2.0); } } /// A 2D linear gradient. /// /// This class is used by [BoxDecoration] to represent gradients. This abstracts /// out the arguments to the [new ui.Gradient.linear] constructor from the /// `dart:ui` library. /// /// A gradient has two anchor points, [begin] and [end]. The [begin] point /// corresponds to 0.0, and the [end] point corresponds to 1.0. These points are /// expressed in fractions, so that the same gradient can be reused with varying /// sized boxes without changing the parameters. (This contrasts with [new /// ui.Gradient.linear], whose arguments are expressed in logical pixels.) /// /// The [colors] are described by a list of [Color] objects. There must be at /// least two colors. The [stops] list, if specified, must have the same length /// as [colors]. It specifies fractions of the vector from start to end, between /// 0.0 and 1.0, for each color. If it is null, a uniform distribution is /// assumed. /// /// The region of the canvas before [begin] and after [end] is colored according /// to [tileMode]. /// /// Typically this class is used with [BoxDecoration], which does the painting. /// To use a [LinearGradient] to paint on a canvas directly, see [createShader]. /// /// ## Sample code /// /// This sample draws a picture that looks like vertical window shades by having /// a [Container] display a [BoxDecoration] with a [LinearGradient]. /// /// ```dart /// new Container( /// decoration: new BoxDecoration( /// gradient: new LinearGradient( /// begin: Alignment.topLeft, /// end: new Alignment(0.8, 0.0), // 10% of the width, so there are ten blinds. /// colors: [const Color(0xFFFFFFEE), const Color(0xFF999999)], // whitish to gray /// tileMode: TileMode.repeated, // repeats the gradient over the canvas /// ), /// ), /// ) /// ``` /// /// See also: /// /// * [RadialGradient], which displays a gradient in concentric circles, and /// has an example which shows a different way to use [Gradient] objects. /// * [BoxDecoration], which can take a [LinearGradient] in its /// [BoxDecoration.gradient] property. class LinearGradient extends Gradient { /// Creates a linear gradient. /// /// The [colors] argument must not be null. If [stops] is non-null, it must /// have the same length as [colors]. const LinearGradient({ this.begin: Alignment.centerLeft, this.end: Alignment.centerRight, @required List<Color> colors, List<double> stops, this.tileMode: TileMode.clamp, }) : assert(begin != null), assert(end != null), assert(tileMode != null), super(colors: colors, stops: stops); /// The offset at which stop 0.0 of the gradient is placed. /// /// If this is a [Alignment], then it is expressed as a vector from /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0). /// /// For example, a begin offset of (-1.0, 0.0) is half way down the /// left side of the box. /// /// It can also be a [AlignmentDirectional], where the start is the /// left in left-to-right contexts and the right in right-to-left contexts. If /// a text-direction-dependent value is provided here, then the [createShader] /// method will need to be given a [TextDirection]. final AlignmentGeometry begin; /// The offset at which stop 1.0 of the gradient is placed. /// /// If this is a [Alignment], then it is expressed as a vector from /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0). /// /// For example, a begin offset of (1.0, 0.0) is half way down the /// right side of the box. /// /// It can also be a [AlignmentDirectional], where the start is the left in /// left-to-right contexts and the right in right-to-left contexts. If a /// text-direction-dependent value is provided here, then the [createShader] /// method will need to be given a [TextDirection]. final AlignmentGeometry end; /// How this gradient should tile the plane beyond in the region before /// [begin] and after [end]. /// /// For details, see [TileMode]. /// ///  ///  ///  final TileMode tileMode; @override Shader createShader(Rect rect, { TextDirection textDirection }) { return new ui.Gradient.linear( begin.resolve(textDirection).withinRect(rect), end.resolve(textDirection).withinRect(rect), colors, _impliedStops(), tileMode, ); } /// Returns a new [LinearGradient] with its properties (in particular the /// colors) scaled by the given factor. /// /// If the factor is 0.0 or less, then the gradient is fully transparent. @override LinearGradient scale(double factor) { return new LinearGradient( begin: begin, end: end, colors: colors.map<Color>((Color color) => Color.lerp(null, color, factor)).toList(), stops: stops, tileMode: tileMode, ); } @override Gradient lerpFrom(Gradient a, double t) { if (a == null || (a is LinearGradient && a.colors.length == colors.length)) // TODO(ianh): remove limitation return LinearGradient.lerp(a, this, t); return super.lerpFrom(a, t); } @override Gradient lerpTo(Gradient b, double t) { if (b == null || (b is LinearGradient && b.colors.length == colors.length)) // TODO(ianh): remove limitation return LinearGradient.lerp(this, b, t); return super.lerpTo(b, t); } /// Linearly interpolate between two [LinearGradient]s. /// /// If either gradient is null, this function linearly interpolates from a /// a gradient that matches the other gradient in [begin], [end], [stops] and /// [tileMode] and with the same [colors] but transparent (using [scale]). /// /// If neither gradient is null, they must have the same number of [colors]. /// /// The `t` argument represents position on the timeline, with 0.0 meaning /// that the interpolation has not started, returning `a` (or something /// equivalent to `a`), 1.0 meaning that the interpolation has finished, /// returning `b` (or something equivalent to `b`), and values in between /// meaning that the interpolation is at the relevant point on the timeline /// between `a` and `b`. The interpolation can be extrapolated beyond 0.0 and /// 1.0, so negative values and values greater than 1.0 are valid (and can /// easily be generated by curves such as [Curves.elasticInOut]). /// /// Values for `t` are usually obtained from an [Animation<double>], such as /// an [AnimationController]. static LinearGradient lerp(LinearGradient a, LinearGradient b, double t) { assert(t != null); if (a == null && b == null) return null; if (a == null) return b.scale(t); if (b == null) return a.scale(1.0 - t); final _ColorsAndStops interpolated = _interpolateColorsAndStops(a.colors, a.stops, b.colors, b.stops, t); return new LinearGradient( begin: AlignmentGeometry.lerp(a.begin, b.begin, t), end: AlignmentGeometry.lerp(a.end, b.end, t), colors: interpolated.colors, stops: interpolated.stops, tileMode: t < 0.5 ? a.tileMode : b.tileMode, // TODO(ianh): interpolate tile mode ); } @override bool operator ==(dynamic other) { if (identical(this, other)) return true; if (runtimeType != other.runtimeType) return false; final LinearGradient typedOther = other; if (begin != typedOther.begin || end != typedOther.end || tileMode != typedOther.tileMode || colors?.length != typedOther.colors?.length || stops?.length != typedOther.stops?.length) return false; if (colors != null) { assert(typedOther.colors != null); assert(colors.length == typedOther.colors.length); for (int i = 0; i < colors.length; i += 1) { if (colors[i] != typedOther.colors[i]) return false; } } if (stops != null) { assert(typedOther.stops != null); assert(stops.length == typedOther.stops.length); for (int i = 0; i < stops.length; i += 1) { if (stops[i] != typedOther.stops[i]) return false; } } return true; } @override int get hashCode => hashValues(begin, end, tileMode, hashList(colors), hashList(stops)); @override String toString() { return '$runtimeType($begin, $end, $colors, $stops, $tileMode)'; } } /// A 2D radial gradient. /// /// This class is used by [BoxDecoration] to represent gradients. This abstracts /// out the arguments to the [new ui.Gradient.radial] constructor from the /// `dart:ui` library. /// /// A gradient has a [center] and a [radius]. The [center] point corresponds to /// 0.0, and the ring at [radius] from the center corresponds to 1.0. These /// lengths are expressed in fractions, so that the same gradient can be reused /// with varying sized boxes without changing the parameters. (This contrasts /// with [new ui.Gradient.radial], whose arguments are expressed in logical /// pixels.) /// /// The [colors] are described by a list of [Color] objects. There must be at /// least two colors. The [stops] list, if specified, must have the same length /// as [colors]. It specifies fractions of the radius between 0.0 and 1.0, /// giving concentric rings for each color stop. If it is null, a uniform /// distribution is assumed. /// /// The region of the canvas beyond [radius] from the [center] is colored /// according to [tileMode]. /// /// Typically this class is used with [BoxDecoration], which does the painting. /// To use a [RadialGradient] to paint on a canvas directly, see [createShader]. /// /// ## Sample code /// /// This function draws a gradient that looks like a sun in a blue sky. /// /// ```dart /// void paintSky(Canvas canvas, Rect rect) { /// var gradient = new RadialGradient( /// center: const Alignment(0.7, -0.6), // near the top right /// radius: 0.2, /// colors: [ /// const Color(0xFFFFFF00), // yellow sun /// const Color(0xFF0099FF), // blue sky /// ], /// stops: [0.4, 1.0], /// ); /// // rect is the area we are painting over /// var paint = new Paint() /// ..shader = gradient.createShader(rect); /// canvas.drawRect(rect, paint); /// } /// ``` /// /// See also: /// /// * [LinearGradient], which displays a gradient in parallel lines, and has an /// example which shows a different way to use [Gradient] objects. /// * [BoxDecoration], which can take a [RadialGradient] in its /// [BoxDecoration.gradient] property. /// * [CustomPainter], which shows how to use the above sample code in a custom /// painter. class RadialGradient extends Gradient { /// Creates a radial gradient. /// /// The [colors] argument must not be null. If [stops] is non-null, it must /// have the same length as [colors]. const RadialGradient({ this.center: Alignment.center, this.radius: 0.5, @required List<Color> colors, List<double> stops, this.tileMode: TileMode.clamp, }) : assert(center != null), assert(radius != null), assert(tileMode != null), super(colors: colors, stops: stops); /// The center of the gradient, as an offset into the (-1.0, -1.0) x (1.0, 1.0) /// square describing the gradient which will be mapped onto the paint box. /// /// For example, an alignment of (0.0, 0.0) will place the radial /// gradient in the center of the box. /// /// If this is a [Alignment], then it is expressed as a vector from /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0). /// /// It can also be a [AlignmentDirectional], where the start is the left in /// left-to-right contexts and the right in right-to-left contexts. If a /// text-direction-dependent value is provided here, then the [createShader] /// method will need to be given a [TextDirection]. final AlignmentGeometry center; /// The radius of the gradient, as a fraction of the shortest side /// of the paint box. /// /// For example, if a radial gradient is painted on a box that is /// 100.0 pixels wide and 200.0 pixels tall, then a radius of 1.0 /// will place the 1.0 stop at 100.0 pixels from the [center]. final double radius; /// How this gradient should tile the plane beyond the outer ring at [radius] /// pixels from the [center]. /// /// For details, see [TileMode]. /// ///  ///  ///  final TileMode tileMode; @override Shader createShader(Rect rect, { TextDirection textDirection }) { return new ui.Gradient.radial( center.resolve(textDirection).withinRect(rect), radius * rect.shortestSide, colors, _impliedStops(), tileMode, ); } /// Returns a new [RadialGradient] with its colors scaled by the given factor. /// /// If the factor is 0.0 or less, then the gradient is fully transparent. @override RadialGradient scale(double factor) { return new RadialGradient( center: center, radius: radius, colors: colors.map<Color>((Color color) => Color.lerp(null, color, factor)).toList(), stops: stops, tileMode: tileMode, ); } @override Gradient lerpFrom(Gradient a, double t) { if (a == null || (a is RadialGradient && a.colors.length == colors.length)) // TODO(ianh): remove limitation return RadialGradient.lerp(a, this, t); return super.lerpFrom(a, t); } @override Gradient lerpTo(Gradient b, double t) { if (b == null || (b is RadialGradient && b.colors.length == colors.length)) // TODO(ianh): remove limitation return RadialGradient.lerp(this, b, t); return super.lerpTo(b, t); } /// Linearly interpolate between two [RadialGradient]s. /// /// If either gradient is null, this function linearly interpolates from a /// a gradient that matches the other gradient in [center], [radius], [stops] and /// [tileMode] and with the same [colors] but transparent (using [scale]). /// /// If neither gradient is null, they must have the same number of [colors]. /// /// The `t` argument represents position on the timeline, with 0.0 meaning /// that the interpolation has not started, returning `a` (or something /// equivalent to `a`), 1.0 meaning that the interpolation has finished, /// returning `b` (or something equivalent to `b`), and values in between /// meaning that the interpolation is at the relevant point on the timeline /// between `a` and `b`. The interpolation can be extrapolated beyond 0.0 and /// 1.0, so negative values and values greater than 1.0 are valid (and can /// easily be generated by curves such as [Curves.elasticInOut]). /// /// Values for `t` are usually obtained from an [Animation<double>], such as /// an [AnimationController]. static RadialGradient lerp(RadialGradient a, RadialGradient b, double t) { assert(t != null); if (a == null && b == null) return null; if (a == null) return b.scale(t); if (b == null) return a.scale(1.0 - t); final _ColorsAndStops interpolated = _interpolateColorsAndStops(a.colors, a.stops, b.colors, b.stops, t); return new RadialGradient( center: AlignmentGeometry.lerp(a.center, b.center, t), radius: math.max(0.0, ui.lerpDouble(a.radius, b.radius, t)), colors: interpolated.colors, stops: interpolated.stops, tileMode: t < 0.5 ? a.tileMode : b.tileMode, // TODO(ianh): interpolate tile mode ); } @override bool operator ==(dynamic other) { if (identical(this, other)) return true; if (runtimeType != other.runtimeType) return false; final RadialGradient typedOther = other; if (center != typedOther.center || radius != typedOther.radius || tileMode != typedOther.tileMode || colors?.length != typedOther.colors?.length || stops?.length != typedOther.stops?.length) return false; if (colors != null) { assert(typedOther.colors != null); assert(colors.length == typedOther.colors.length); for (int i = 0; i < colors.length; i += 1) { if (colors[i] != typedOther.colors[i]) return false; } } if (stops != null) { assert(typedOther.stops != null); assert(stops.length == typedOther.stops.length); for (int i = 0; i < stops.length; i += 1) { if (stops[i] != typedOther.stops[i]) return false; } } return true; } @override int get hashCode => hashValues(center, radius, tileMode, hashList(colors), hashList(stops)); @override String toString() { return '$runtimeType($center, $radius, $colors, $stops, $tileMode)'; } }