Creates a mask filter that takes the shape being drawn and blurs it.
This is commonly used to approximate shadows.
style argument controls the kind of effect to draw; see BlurStyle.
sigma argument controls the size of the effect. It is the standard
deviation of the Gaussian blur to apply. The value must be greater than
zero. The sigma corresponds to very roughly half the radius of the effect
A blur is an expensive operation and should therefore be used sparingly.
The arguments must not be null.
- Canvas.drawShadow, which is a more efficient way to draw shadows.
const MaskFilter.blur( this._style, this._sigma, ) : assert(_style != null), assert(_sigma != null);