diagonal

def diagonal(pict,x,y,color):
#@param:
#   pict: picture;
#   x: int, starting x coordinate;
#   y: int, starting y coordinate;
#   color: color;
    width = getWidth(pict)
    height = getHeight(pict)
    assert x<width and y<height and x>=0 and y>=0, "Invalid parameters, x or y is smaller than 0 or bigger than picture size."
    i = 0
    while i<width-x and i<height-y:
        pix = getPixel(pict,x+i,y+i)
        setColor(pix,color)
        i +=1