opacity method
Create new filter from this filter with given opacity
Implementation
ColorFilterGenerator opacity(double value) {
return ColorFilterGenerator(
name: name,
filters: <List<double>>[
...filters,
<double>[
value,
0,
0,
0,
0,
0,
value,
0,
0,
0,
0,
0,
value,
0,
0,
0,
0,
0,
1,
0,
],
],
);
}