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// Copyright 2016 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 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/rendering.dart';
import 'scroll_metrics.dart';
const double _kMinThumbExtent = 18.0;
/// A [CustomPainter] for painting scrollbars.
///
/// Unlike [CustomPainter]s that subclasses [CustomPainter] and only repaint
/// when [shouldRepaint] returns true (which requires this [CustomPainter] to
/// be rebuilt), this painter has the added optimization of repainting and not
/// rebuilding when:
///
/// * the scroll position changes; and
/// * when the scrollbar fades away.
///
/// Calling [update] with the new [ScrollMetrics] will repaint the new scrollbar
/// position.
///
/// Updating the value on the provided [fadeoutOpacityAnimation] will repaint
/// with the new opacity.
///
/// You must call [dispose] on this [ScrollbarPainter] when it's no longer used.
///
/// See also:
///
/// * [Scrollbar] for a widget showing a scrollbar around a [Scrollable] in the
/// Material Design style.
/// * [CupertinoScrollbar] for a widget showing a scrollbar around a
/// [Scrollable] in the iOS style.
class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
/// Creates a scrollbar with customizations given by construction arguments.
ScrollbarPainter({
@required this.color,
@required this.textDirection,
@required this.thickness,
@required this.fadeoutOpacityAnimation,
this.mainAxisMargin: 0.0,
this.crossAxisMargin: 0.0,
this.radius,
this.minLength: _kMinThumbExtent,
}) : assert(color != null),
assert(textDirection != null),
assert(thickness != null),
assert(fadeoutOpacityAnimation != null),
assert(mainAxisMargin != null),
assert(crossAxisMargin != null),
assert(minLength != null) {
fadeoutOpacityAnimation.addListener(notifyListeners);
}
/// [Color] of the thumb. Mustn't be null.
final Color color;
/// [TextDirection] of the [BuildContext] which dictates the side of the
/// screen the scrollbar appears in (the trailing side). Mustn't be null.
final TextDirection textDirection;
/// Thickness of the scrollbar in its cross-axis in pixels. Mustn't be null.
final double thickness;
/// An opacity [Animation] that dictates the opacity of the thumb.
/// Changes in value of this [Listenable] will automatically trigger repaints.
/// Mustn't be null.
final Animation<double> fadeoutOpacityAnimation;
/// Distance from the scrollbar's start and end to the edge of the viewport in
/// pixels. Mustn't be null.
final double mainAxisMargin;
/// Distance from the scrollbar's side to the nearest edge in pixels. Musn't
/// be null.
final double crossAxisMargin;
/// [Radius] of corners if the scrollbar should have rounded corners.
///
/// Scrollbar will be rectangular if [radius] is null.
final Radius radius;
/// The smallest size the scrollbar can shrink to when the total scrollable
/// extent is large and the current visible viewport is small. Mustn't be
/// null.
final double minLength;
ScrollMetrics _lastMetrics;
AxisDirection _lastAxisDirection;
/// Update with new [ScrollMetrics]. The scrollbar will show and redraw itself
/// based on these new metrics.
///
/// The scrollbar will remain on screen.
void update(
ScrollMetrics metrics,
AxisDirection axisDirection,
) {
_lastMetrics = metrics;
_lastAxisDirection = axisDirection;
notifyListeners();
}
Paint get _paint {
return new Paint()..color =
color.withOpacity(color.opacity * fadeoutOpacityAnimation.value);
}
double _getThumbX(Size size) {
assert(textDirection != null);
switch (textDirection) {
case TextDirection.rtl:
return crossAxisMargin;
case TextDirection.ltr:
return size.width - thickness - crossAxisMargin;
}
return null;
}
void _paintVerticalThumb(Canvas canvas, Size size, double thumbOffset, double thumbExtent) {
final Offset thumbOrigin = new Offset(_getThumbX(size), thumbOffset);
final Size thumbSize = new Size(thickness, thumbExtent);
final Rect thumbRect = thumbOrigin & thumbSize;
if (radius == null)
canvas.drawRect(thumbRect, _paint);
else
canvas.drawRRect(new RRect.fromRectAndRadius(thumbRect, radius), _paint);
}
void _paintHorizontalThumb(Canvas canvas, Size size, double thumbOffset, double thumbExtent) {
final Offset thumbOrigin = new Offset(thumbOffset, size.height - thickness);
final Size thumbSize = new Size(thumbExtent, thickness);
final Rect thumbRect = thumbOrigin & thumbSize;
if (radius == null)
canvas.drawRect(thumbRect, _paint);
else
canvas.drawRRect(new RRect.fromRectAndRadius(thumbRect, radius), _paint);
}
void _paintThumb(
double before,
double inside,
double after,
double viewport,
Canvas canvas,
Size size,
void painter(Canvas canvas, Size size, double thumbOffset, double thumbExtent),
) {
// Establish the minimum size possible.
double thumbExtent = math.min(viewport, minLength);
if (before + inside + after > 0.0) {
final double fractionVisible = inside / (before + inside + after);
thumbExtent = math.max(
thumbExtent,
viewport * fractionVisible - 2 * mainAxisMargin,
);
}
final double fractionPast = before / (before + after);
final double thumbOffset = (before + after > 0.0)
? fractionPast * (viewport - thumbExtent - 2 * mainAxisMargin) + mainAxisMargin
: mainAxisMargin;
painter(canvas, size, thumbOffset, thumbExtent);
}
@override
void dispose() {
fadeoutOpacityAnimation.removeListener(notifyListeners);
super.dispose();
}
@override
void paint(Canvas canvas, Size size) {
if (_lastAxisDirection == null
|| _lastMetrics == null
|| fadeoutOpacityAnimation.value == 0.0)
return;
switch (_lastAxisDirection) {
case AxisDirection.down:
_paintThumb(_lastMetrics.extentBefore, _lastMetrics.extentInside, _lastMetrics.extentAfter, size.height, canvas, size, _paintVerticalThumb);
break;
case AxisDirection.up:
_paintThumb(_lastMetrics.extentAfter, _lastMetrics.extentInside, _lastMetrics.extentBefore, size.height, canvas, size, _paintVerticalThumb);
break;
case AxisDirection.right:
_paintThumb(_lastMetrics.extentBefore, _lastMetrics.extentInside, _lastMetrics.extentAfter, size.width, canvas, size, _paintHorizontalThumb);
break;
case AxisDirection.left:
_paintThumb(_lastMetrics.extentAfter, _lastMetrics.extentInside, _lastMetrics.extentBefore, size.width, canvas, size, _paintHorizontalThumb);
break;
}
}
// Scrollbars are (currently) not interactive.
@override
bool hitTest(Offset position) => null;
@override
bool shouldRepaint(ScrollbarPainter old) {
// Should repaint if any properties changed.
return color != old.color
|| textDirection != old.textDirection
|| thickness != old.thickness
|| fadeoutOpacityAnimation != old.fadeoutOpacityAnimation
|| mainAxisMargin != old.mainAxisMargin
|| crossAxisMargin != old.crossAxisMargin
|| radius != old.radius
|| minLength != old.minLength;
}
@override
bool shouldRebuildSemantics(CustomPainter oldDelegate) => false;
@override
SemanticsBuilderCallback get semanticsBuilder => null;
}