gtShiftContour.m

function [x,y]=gtShiftContour(x,y,shiftx,shifty,sizex,sizey)

if (x<1) || (y<1)
  error('X and Y must be inside the sizex,sizey pair')
end
x=mod(x+shiftx-1,sizex)+1;
y=mod(y+shifty-1,sizey)+1;