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Make the edge gradients fade in smoothly as you scroll, depending on the scroll position #32

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Make the edge gradients fade in smoothly as you scroll, depending on the scroll position #32

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243475e
Make the edge gradients fade in smoothly as you scroll, depending on …
timurrrr Jul 29, 2025
47450f3
Use the layout bounds instead of total scrollable length to control t…
timurrrr Jul 30, 2025
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76 changes: 35 additions & 41 deletions lib/src/fading_edge_scrollview.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -171,7 +171,10 @@ class FadingEdgeScrollView extends StatefulWidget {
class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>
with WidgetsBindingObserver {
late ScrollController _controller;
_ScrollState _scrollState = _ScrollState.notScrollable;

double _offsetFromStart = 0;
double _offsetFromEnd = 0;

int lastScrollViewListLength = 0;

@override
Expand Down Expand Up @@ -202,7 +205,11 @@ class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>

@override
Widget build(BuildContext context) => ShaderMask(
shaderCallback: (bounds) => _createShaderGradient().createShader(
shaderCallback: (bounds) => _createShaderGradient(
widget.scrollDirection == Axis.vertical
? bounds.height
: bounds.width)
.createShader(
bounds.shift(Offset(-bounds.left, -bounds.top)),
textDirection: Directionality.of(context),
),
Expand All @@ -220,7 +227,7 @@ class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>
),
);

Gradient _createShaderGradient() => LinearGradient(
Gradient _createShaderGradient(double size) => LinearGradient(
begin: _gradientStart,
end: _gradientEnd,
stops: [
Expand All @@ -229,11 +236,16 @@ class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>
1 - widget.gradientFractionOnEnd * 0.5,
1,
],
colors: _getColors(
widget.gradientFractionOnStart > 0 &&
_scrollState.isShowGradientAtStart,
widget.gradientFractionOnEnd > 0 &&
_scrollState.isShowGradientAtEnd),
colors: <Color>[
widget.gradientFractionOnStart > 0
? fadeInColor(_offsetFromStart, size * widget.gradientFractionOnStart)
: Colors.white,
Colors.white,
Colors.white,
widget.gradientFractionOnEnd > 0
? fadeInColor(_offsetFromEnd, size * widget.gradientFractionOnEnd)
: Colors.white
]
);

AlignmentGeometry get _gradientStart =>
Expand All @@ -258,12 +270,16 @@ class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>
? AlignmentDirectional.centerStart
: AlignmentDirectional.centerEnd;

List<Color> _getColors(bool showGradientAtStart, bool showGradientAtEnd) => [
(showGradientAtStart ? Colors.transparent : Colors.white),
Colors.white,
Colors.white,
(showGradientAtEnd ? Colors.transparent : Colors.white)
];
Color fadeInColor(double offsetFromEdge, double threshold) {
if (offsetFromEdge <= 0) {
return Colors.white;
}
if (offsetFromEdge >= threshold) {
return Colors.transparent;
}
int alpha = 255 - (255 * offsetFromEdge / threshold).round();
return Color.fromARGB(alpha, 255, 255, 255);
}

void _updateScrollState() {
if (!_controllerIsReady) {
Expand All @@ -274,35 +290,13 @@ class FadingEdgeScrollViewState extends State<FadingEdgeScrollView>
final minOffset = _controller.positions.last.minScrollExtent;
final maxOffset = _controller.positions.last.maxScrollExtent;

final isScrolledToEnd = offset >= maxOffset;
final isScrolledToStart = offset <= minOffset;

final scrollState = switch ((isScrolledToStart, isScrolledToEnd)) {
(true, true) => _ScrollState.notScrollable,
(true, false) => _ScrollState.scrollableAtStart,
(false, true) => _ScrollState.scrollableAtEnd,
(false, false) => _ScrollState.scrollableInTheMiddle
};

if (_scrollState != scrollState) {
final offsetFromStart = offset - minOffset;
final offsetFromEnd = maxOffset - offset;
if (offsetFromStart != _offsetFromStart || offsetFromEnd != _offsetFromEnd) {
setState(() {
_scrollState = scrollState;
_offsetFromStart = offsetFromStart;
_offsetFromEnd = offsetFromEnd;
});
}
}
}

enum _ScrollState {
notScrollable,
scrollableAtStart,
scrollableAtEnd,
scrollableInTheMiddle;

bool get isShowGradientAtStart =>
this == _ScrollState.scrollableAtEnd ||
this == _ScrollState.scrollableInTheMiddle;

bool get isShowGradientAtEnd =>
this == _ScrollState.scrollableAtStart ||
this == _ScrollState.scrollableInTheMiddle;
}