paintOpacity method
Implementation
void paintOpacity(PaintingContext context, Offset offset,
PaintingContextCallback callback) {
if (alpha == 255) {
_opacityLayer.layer = null;
// No need to keep the layer. We'll create a new one if necessary.
callback(context, offset);
return;
}
_opacityLayer.layer =
context.pushOpacity(offset, alpha, callback, oldLayer: _opacityLayer.layer);
}