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Offset.direction (flutter/engine#4530)

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Since we've got a vector class, and it has a getter for the magnitude,
why not also a getter for the angle.
This commit is contained in:
Ian Hickson 2018-01-09 22:17:57 -08:00 committed by GitHub
parent 495f8f71f4
commit 39ba4de88b
2 changed files with 51 additions and 0 deletions
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29
engine/src/flutter/lib/ui/geometry.dart
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@ -142,6 +142,35 @@ class Offset extends OffsetBase {
/// This is cheaper than computing the [distance] itself.
double get distanceSquared => _dx * _dx + _dy * _dy;
/// The angle of this offset as radians clockwise from the positive x-axis, in
/// the range -[pi] to [pi], assuming positive values of the x-axis go to the
/// left and positive values of the y-axis go down.
///
/// Zero means that [dy] is zero and [dx] is zero or positive.
///
/// Values from zero to [pi]/2 indicate positive values of [dx] and [dy], the
/// bottom-right quadrant.
///
/// Values from [pi]/2 to [pi] indicate negative values of [dx] and positive
/// values of [dy], the bottom-left quadrant.
///
/// Values from zero to -[pi]/2 indicate positive values of [dx] and negative
/// values of [dy], the top-right quadrant.
///
/// Values from -[pi]/2 to -[pi] indicate negative values of [dx] and [dy],
/// the top-left quadrant.
///
/// When [dy] is zero and [dx] is negative, the [direction] is [pi].
///
/// When [dx] is zero, [direction] is [pi]/2 if [dy] is positive and -[pi]/2
/// if [dy] is negative.
///
/// See also:
///
/// * [distance], to compute the magnitude of the vector.
/// * [Canvas.rotate], which uses the same convention for its angle.
double get direction => math.atan2(dy, dx);
/// An offset with zero magnitude.
///
/// This can be used to represent the origin of a coordinate space.

22
engine/src/flutter/testing/dart/geometry_test.dart Normal file
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@ -0,0 +1,22 @@
// Copyright 2018 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:ui';
import 'dart:math' show pi;
import 'package:test/test.dart';
void main() {
test('Offset.direction', () {
expect(const Offset(0.0, 0.0).direction, 0.0);
expect(const Offset(0.0, 1.0).direction, pi / 2.0);
expect(const Offset(0.0, -1.0).direction, -pi / 2.0);
expect(const Offset(1.0, 0.0).direction, 0.0);
expect(const Offset(1.0, 1.0).direction, pi / 4.0);
expect(const Offset(1.0, -1.0).direction, -pi / 4.0);
expect(const Offset(-1.0, 0.0).direction, pi);
expect(const Offset(-1.0, 1.0).direction, pi * 3.0 / 4.0);
expect(const Offset(-1.0, -1.0).direction, -pi * 3.0 / 4.0);
});
}