PGF equivalent of PostScript relative movement (`rlineto` and `rmoveto`)

In the following example, two new macros pgfpathrlineto{<coord>} and pgfpathrmoveto{<coord>} are provided. They are not fully tested, so be careful.

Actually, we need to keep track of the original (un-transformed) coordinates of last point, but here pgf@x and pgf@y store transformed coordinates.

The point is, in (x, y) -- ++(2, 3), the expected line before transforming is (x, y) -- (x+2, y+3), while what I implemented in the following example is (x, y) -- ($ (x, y) + T'(2, 3) $), where T' is the inversion of transformation.

documentclass{article}
usepackage{pgf}

makeatletter
defpgf@path@last@point{%
  pgfpoint{pgf@path@lastx}{pgf@path@lasty}}

% rlineto
defpgfpathrlineto#1{%
  pgf@process{#1}%
  globaladvancepgf@xpgf@path@lastx
  globaladvancepgf@ypgf@path@lasty
  % similar to pgfpathlineto, but without applying transformation
  pgf@nlt@lineto{pgf@x}{pgf@y}%
  globalpgf@path@lastx=pgf@x
  globalpgf@path@lasty=pgf@y
}

% rmoveto
defpgfpathrmoveto#1{%
  pgf@process{#1}%
  globaladvancepgf@xpgf@path@lastx
  globaladvancepgf@ypgf@path@lasty
  % similar to pgfpathlineto, but without applying transformation
  pgf@nlt@moveto{pgf@x}{pgf@y}%
  globalpgf@path@lastx=pgf@x
  globalpgf@path@lasty=pgf@y
}
makeatother

begin{document}
begin{pgfpicture}
  pgfpathmoveto{pgfpointorigin}
  pgfpathlineto{pgfpoint{20pt}{0pt}}
  pgfpathmoveto{pgfpoint{40pt}{0pt}}
  pgfpathlineto{pgfpoint{60pt}{0pt}}
  pgfusepath{draw}
  
  pgftransformshift{pgfpoint{10pt}{10pt}}
  pgfsetcolor{red}
  pgfpathmoveto{pgfpointorigin}
  pgfpathlineto{pgfpoint{20pt}{0pt}}
  pgfpathmoveto{pgfpoint{40pt}{0pt}}
  pgfpathlineto{pgfpoint{60pt}{0pt}}
  pgfusepath{draw}
end{pgfpicture}
qquad
% use r(line|move)to
begin{pgfpicture}
  pgfpathmoveto{pgfpointorigin}
  pgfpathrlineto{pgfpoint{20pt}{0pt}}
  pgfpathrmoveto{pgfpoint{20pt}{0pt}}
  pgfpathrlineto{pgfpoint{20pt}{0pt}}
  pgfusepath{draw}
  
  pgftransformshift{pgfpoint{10pt}{10pt}}
  pgfsetcolor{red}
  pgfpathmoveto{pgfpointorigin}
  pgfpathrlineto{pgfpoint{20pt}{0pt}}
  pgfpathrmoveto{pgfpoint{20pt}{0pt}}
  pgfpathrlineto{pgfpoint{20pt}{0pt}}
  pgfusepath{draw}
end{pgfpicture}
end{document}