blob: dd041631ad37b9bdcdc2d7898b740c7fd3f7a86d [file] [log] [blame]
import 'dart:math' as math;
import 'basic_types.dart';
/// A shape with a notch in its outline.
///
/// Typically used as the outline of a 'host' widget to make a notch that
/// accomodates a 'guest' widget. e.g the [BottomAppBar] may have a notch to
/// accomodate the [FloatingActionBar].
/// See also: [ShapeBorder], which defines a shaped border without a dynamic
/// notch.
abstract class NotchedShape {
/// Abstract const constructor. This constructor enables subclasses to provide
/// const constructors so that they can be used in const expressions.
const NotchedShape();
/// Creates a [Path] that describes the outline of the shape.
///
/// The `host` is the bounding rectangle of the shape.
///
/// Rhe `guest` is the bounding rectangle of the shape for which a notch will
/// be made.
Path getOuterPath(Rect host, Rect guest);
}
/// A rectangle with a smooth circular notch.
class CircularNotchedRectangle implements NotchedShape {
/// Creates a `CircularNotchedRectangle`.
///
/// The same object can be used to create multiple shapes.
const CircularNotchedRectangle();
/// Creates a [Path] that describes a rectangle with a smooth circular notch.
///
/// `host` is the bounding box for the returned shape. Conceptually this is
/// the rectangle to which the notch will be applied.
///
/// `guest` is the bounding box of a circle that the notch accomodates. All
/// points in the circle bounded by `guest` will be outside of the returned
/// path.
///
/// The notch is curve that smoothly connects the host's top edge and
/// the guest circle.
// TODO(amirh): add an example diagram here.
@override
Path getOuterPath(Rect host, Rect guest) {
if (!host.overlaps(guest))
return Path()..addRect(host);
// The guest's shape is a circle bounded by the guest rectangle.
// So the guest's radius is half the guest width.
final double notchRadius = guest.width / 2.0;
// We build a path for the notch from 3 segments:
// Segment A - a Bezier curve from the host's top edge to segment B.
// Segment B - an arc with radius notchRadius.
// Segment C - a Bezier curver from segment B back to the host's top edge.
//
// A detailed explanation and the derivation of the formulas below is
// available at: https://goo.gl/Ufzrqn
const double s1 = 15.0;
const double s2 = 1.0;
final double r = notchRadius;
final double a = -1.0 * r - s2;
final double b = host.top - guest.center.dy;
final double n2 = math.sqrt(b * b * r * r * (a * a + b * b - r * r));
final double p2xA = ((a * r * r) - n2) / (a * a + b * b);
final double p2xB = ((a * r * r) + n2) / (a * a + b * b);
final double p2yA = math.sqrt(r * r - p2xA * p2xA);
final double p2yB = math.sqrt(r * r - p2xB * p2xB);
final List<Offset> p = List<Offset>(6);
// p0, p1, and p2 are the control points for segment A.
p[0] = Offset(a - s1, b);
p[1] = Offset(a, b);
final double cmp = b < 0 ? -1.0 : 1.0;
p[2] = cmp * p2yA > cmp * p2yB ? Offset(p2xA, p2yA) : Offset(p2xB, p2yB);
// p3, p4, and p5 are the control points for segment B, which is a mirror
// of segment A around the y axis.
p[3] = Offset(-1.0 * p[2].dx, p[2].dy);
p[4] = Offset(-1.0 * p[1].dx, p[1].dy);
p[5] = Offset(-1.0 * p[0].dx, p[0].dy);
// translate all points back to the absolute coordinate system.
for (int i = 0; i < p.length; i += 1)
p[i] += guest.center;
return Path()
..moveTo(host.left, host.top)
..lineTo(p[0].dx, p[0].dy)
..quadraticBezierTo(p[1].dx, p[1].dy, p[2].dx, p[2].dy)
..arcToPoint(
p[3],
radius: Radius.circular(notchRadius),
clockwise: false,
)
..quadraticBezierTo(p[4].dx, p[4].dy, p[5].dx, p[5].dy)
..lineTo(host.right, host.top)
..lineTo(host.right, host.bottom)
..lineTo(host.left, host.bottom)
..close();
}
}