def replace_row!(y, vector)
      assert_y!(y) && assert_width!(vector.length)
      pixels[y * width, width] = vector
    end
def replace_row!(y, vector)
      assert_y!(y) && assert_width!(vector.length)
      pixels[y * width, width] = vector
    end
Replaces a row of pixels on this canvas.
 @param [Integer] y The 0-based row index.
 @param [Array<Integer>] vector The vector of pixels to replace the row
   with.
 @return [void]