isVisible property
Whether or not the child is actually visible within the viewport.
For example, if a child is contained within the RenderTwoDimensionalViewport.cacheExtent and out of view.
This is used during RenderTwoDimensionalViewport.paint in order to skip painting children that cannot be seen.
Implementation
bool get isVisible {
assert(() {
if (_paintExtent == null) {
throw FlutterError.fromParts(<DiagnosticsNode>[
ErrorSummary('The paint extent of the child has not been determined yet.'),
ErrorDescription(
'The paint extent, and therefore the visibility, of a child of a '
'RenderTwoDimensionalViewport is computed after '
'RenderTwoDimensionalViewport.layoutChildSequence.'
),
]);
}
return true;
}());
return _paintExtent != Size.zero || _paintExtent!.height != 0.0 || _paintExtent!.width != 0.0;
}