PorterDuff constructor
Creates a blend mode with Porter-Duff coefficients.
The src and dst functions are used to calculate the source and destination coefficients, respectively. The result of blending the source and destination colors is calculated as:
final srcAlpha = src(src.w, dst.w);
final dstAlpha = dst(src.w, dst.w);
return src * srcAlpha + dst * dstAlpha;
Implementation
const PorterDuff(this._src, this._dst);