Draws contents of this canvas onto another one with typical alpha blending (Src 'over' Dest, factors are bfSrcAlpha and bfOneMinusSrcAlpha.)

public procedure StretchDrawAlpha(const SrcRect: TRect; 
                                  DestCanvas: TImagingCanvas; 
                                  const DestRect: TRect; 
                                  Filter: TResizeFilter = rfBilinear); override;