opacity property

double opacity

The fraction to scale the child's alpha value.

An opacity of 1.0 is fully opaque. An opacity of 0.0 is fully transparent (i.e., invisible).

The opacity must not be null.

Values 1.0 and 0.0 are painted with a fast path. Other values require painting the child into an intermediate buffer, which is expensive.

Implementation 

double get opacity => _opacity;
void opacity= (double value)

Implementation 

set opacity(double value) {
  assert(value != null);
  assert(value >= 0.0 && value <= 1.0);
  if (_opacity == value)
    return;
  final bool didNeedCompositing = alwaysNeedsCompositing;
  final bool wasVisible = _alpha != 0;
  _opacity = value;
  _alpha = _getAlphaFromOpacity(_opacity);
  if (didNeedCompositing != alwaysNeedsCompositing)
    markNeedsCompositingBitsUpdate();
  markNeedsPaint();
  if (wasVisible != (_alpha != 0))
    markNeedsSemanticsUpdate();
}