firka/flutter
firka/flutter
4
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Remove floating-point errors from ScrollableWidgetList

Browse Source 
We now compute which items to show using integers instead of floating point,
avoiding rounding errors.
This commit is contained in:
Adam Barth 2015-08-24 16:20:22 -07:00
parent 14f3f58cd9
commit c696c21aa5
1 changed files with 5 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
packages/flutter/lib/widgets/scrollable.dart
View File

@ -338,8 +338,6 @@ class Block extends Component {
/// widget when you have a large number of children or when you are concerned /// widget when you have a large number of children or when you are concerned
// about offscreen widgets consuming resources. // about offscreen widgets consuming resources.
abstract class ScrollableWidgetList extends Scrollable { abstract class ScrollableWidgetList extends Scrollable {
static const _kEpsilon = .0000001;
ScrollableWidgetList({ ScrollableWidgetList({
Key key, Key key,
ScrollDirection scrollDirection: ScrollDirection.vertical, ScrollDirection scrollDirection: ScrollDirection.vertical,
@ -445,24 +443,13 @@ abstract class ScrollableWidgetList extends Scrollable {
if (paddedScrollOffset < scrollBehavior.minScrollOffset) { if (paddedScrollOffset < scrollBehavior.minScrollOffset) {
// Underscroll // Underscroll
double visibleExtent = _containerExtent + paddedScrollOffset; double visibleExtent = _containerExtent + paddedScrollOffset;
itemShowCount = (visibleExtent / itemExtent).round() + 1; itemShowCount = (visibleExtent / itemExtent).ceil();
viewportOffset = _toOffset(paddedScrollOffset); viewportOffset = _toOffset(paddedScrollOffset);
} else { } else {
itemShowCount = (_containerExtent / itemExtent).ceil(); itemShowCount = (_containerExtent / itemExtent).ceil() + 1;
double alignmentDelta = (-paddedScrollOffset % itemExtent); itemShowIndex = (paddedScrollOffset / itemExtent).floor();
double drawStart = paddedScrollOffset; viewportOffset = _toOffset(paddedScrollOffset - itemShowIndex * itemExtent);
if (alignmentDelta != 0.0) { itemShowIndex %= itemCount; // Wrap index for when itemWrap is true.
alignmentDelta -= itemExtent;
itemShowCount += 1;
drawStart += alignmentDelta;
viewportOffset = _toOffset(-alignmentDelta);
}
if (itemCount > 0) {
// floor(epsilon) = 0, floor(-epsilon) = -1, so:
if (drawStart.abs() < _kEpsilon)
drawStart = 0.0;
itemShowIndex = (drawStart / itemExtent).floor() % itemCount;
}
} }
} }