Is it possible to use the dist() function to do a spot blur on an image ?

A better algorithm than this one

a=sblur(_a,a.width/2, a.height/2, 45,15);

1. PImage sblur(PImage img,int _x, int _y, float radius,float amt){
    PImage retval = createImage(img.width,img.height,ARGB);
    PImage retval2 = createImage(img.width,img.height,ARGB);
    arraycopy(img.pixels,retval2.pixels);
    retval2.filter(BLUR,amt);
   for (int x=0;x<img.width;x++){
    for (int y=0;y<img.height;y++){
    if(dist(_x,_y,x,y)<radius){
        retval.pixels[x+retval.width*y]=retval2.pixels[ x+retval.width*y];
    }
    else
    {
     retval.pixels[x+retval.width*y]=img.pixels[ x+retval.width*y];
    }
   }
    
   }
   return retval;
   }