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RenderParallax({
required ScrollableState scrollable,
}) : _scrollable = scrollable;
ScrollableState _scrollable;
ScrollableState get scrollable => _scrollable;
set scrollable(ScrollableState value) {
if (value != _scrollable) {
if (attached) {
_scrollable.position.removeListener(markNeedsLayout);
}
_scrollable = value;
if (attached) {
_scrollable.position.addListener(markNeedsLayout);
}
}
}
@override
void attach(covariant PipelineOwner owner) {
super.attach(owner);
_scrollable.position.addListener(markNeedsLayout);
}
@override
void detach() {
_scrollable.position.removeListener(markNeedsLayout);
super.detach();
}
@override
void setupParentData(covariant RenderObject child) {
if (child.parentData is! ParallaxParentData) {
child.parentData = ParallaxParentData();
}
}
@override
void performLayout() {
size = constraints.biggest;
// Force the background to take up all available width
// and then scale its height based on the image's aspect ratio.
final background = child!;
final backgroundImageConstraints =
BoxConstraints.tightFor(width: size.width);
background.layout(backgroundImageConstraints, parentUsesSize: true);
// Set the background's local offset, which is zero.
(background.parentData as ParallaxParentData).offset = Offset.zero;
}
@override
void paint(PaintingContext context, Offset offset) {
// Get the size of the scrollable area.
final viewportDimension = scrollable.position.viewportDimension;
// Calculate the global position of this list item.
final scrollableBox = scrollable.context.findRenderObject() as RenderBox;
final backgroundOffset =
localToGlobal(size.centerLeft(Offset.zero), ancestor: scrollableBox);
// Determine the percent position of this list item within the
// scrollable area.
final scrollFraction =
(backgroundOffset.dy / viewportDimension).clamp(0.0, 1.0);
// Calculate the vertical alignment of the background
// based on the scroll percent.
final verticalAlignment = Alignment(0.0, scrollFraction * 2 - 1);
// Convert the background alignment into a pixel offset for
// painting purposes.
final background = child!;
final backgroundSize = background.size;
final listItemSize = size;
final childRect =
verticalAlignment.inscribe(backgroundSize, Offset.zero & listItemSize);
// Paint the background.
context.paintChild(
background,
(background.parentData as ParallaxParentData).offset +
offset +
Offset(0.0, childRect.top));
}
}
class Location {
const Location({
required this.name,
required this.place,
required this.imageUrl,
});
final String name;
final String place;
final String imageUrl;
}
const urlPrefix =
'https://docs.flutter.dev/cookbook/img-files/effects/parallax';
const locations = [
Location(
name: 'Mount Rushmore',
place: 'U.S.A',
imageUrl: '$urlPrefix/01-mount-rushmore.jpg',
),
Location(
name: 'Gardens By The Bay',
place: 'Singapore',
imageUrl: '$urlPrefix/02-singapore.jpg',
),
Location(
name: 'Machu Picchu',
place: 'Peru',