Connecting to a node towards a point other than the center

Question

I'm trying to connect an edge to a node with the target point being off-center. I would like the edge to end with an arrow at the border of the node without going into the box.

It is easy to connect an edge to a side of a node:

\begin{tikzpicture}
\node (x) [draw,minimum size=1 cm] at (0,0) {x};
\node (y) [draw,minimum size=1 cm] at (2 cm,2 cm) {y};
\draw[->] (x) -- (y.west);
\end{tikzpicture}

But drawing to halfway between (x) and (x.west) continues into the node instead of stopping at the border:

\begin{tikzpicture}
\node (x) [draw,minimum size=1 cm] at (0,0) {x};
\node (y) [draw,minimum size=1 cm] at (2 cm,2 cm) {y};
\draw[->] (x) -- ($ (y.west)!0.5!(y) $);
\end{tikzpicture}

How can I make an edge with the same angle as (x) -- ($ (y.west)!0.5!(y) $) but which draws the arrow right at the border instead of entering into the node?

Answer 1

With the TikZ library intersections you can find the point on the node's rectangle quite easily.

We give the y node a path name: yborder.
We use one \path command to get the path from (x) to ($ (y.west)!0.5!(y) $) and name it xyline.

With name intersections={of=yborder and xyline} we get coordinates named intersections-1, intersections-2, …
In our case there's only one intersection, so intersection-1 will do.

(The PGF/TikZ manual shows how to deal with path intersections with more than one hit.)

Code

\documentclass[tikz,border=2pt]{standalone}
\usetikzlibrary{calc,intersections}
\begin{document}
\begin{tikzpicture}[every node/.style={draw,minimum size=1 cm}]
    \node                     (x) at (0cm,0cm) {x};
    \node [name path=yborder] (y) at (2cm,2cm) {y};
    \path [name path=xyline ] (x) -- ($ (y.west)!0.5!(y) $);
    \fill [red]               ($(y.west)!0.5!(y)$) circle[radius=1pt]; % Where's my point?
    \draw [name intersections={of=yborder and xyline},->]
                              (x) -- (intersection-1);
\end{tikzpicture}
\begin{tikzpicture}[every node/.style={circle,draw,minimum size=1 cm}]
    \node                     (x) at (0cm,0cm) {x};
    \node [name path=yborder] (y) at (2cm,2cm) {y};
    \path [name path=xyline ] (x) -- ($ (y.west)!0.5!(y) $);
    \fill [red]               ($(y.west)!0.5!(y)$) circle[radius=1pt]; % Where's my point?
    \draw [name intersections={of=yborder and xyline},->]
                              (x) -- (intersection-1);
\end{tikzpicture}
\end{document}

Output

Answer 2

You can use shorten :

\draw[->,shorten >=10pt] (x) -- ($ (y.west)!0.5!(y) $);

Code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
\node (x) [draw,minimum size=1 cm] at (0,0) {x};
\node (y) [draw,minimum size=1 cm] at (2 cm,2 cm) {y};
\draw[->] (x) -- (y.west);
\end{tikzpicture}
\begin{tikzpicture}
\node (x) [draw,minimum size=1 cm] at (0,0) {x};
\node (y) [draw,minimum size=1 cm] at (2 cm,2 cm) {y};
\draw[->,shorten >=10pt] (x) -- ($ (y.west)!0.5!(y) $);
\end{tikzpicture}
\end{document}