Drawing a polyline between two nodes in tikz

Question

I am a beginner with tikz and finding the following really difficult to do.

I have defined and drawn node1 and node2 in tikz. You can figure it out easily from the picture. What I intend to do is

• Draw a dashed line from (node1.south) to P1.

• Draw a dashed line from P1 to P2.

• Draw a pointed dashed line from P2 to (node2.north).

• where the point P1 is (node1.south)+(0,-y). y is a positive integer which I am free to choose depending on y-axis distance between node1 and node2.

• and I define the point P2 as the point where a horizontal left-ward line from P1 meets the vertical upward line from (node2.north).
  This thing roughly accomplished in google drawing is shown.

Answer 1

Qrrbrbirlbel's great paths.ortho library is perfect for this. Using the library, you don't have to calculate the support points manually, but instead you can simply write

\draw [dashed, -latex] (A) |-| (B);

to get

or

\draw [dashed, -latex, hvvh/ratio=0.7] (A) |-| (B);

to get

Together with Luigi's awesome arrows.new library, which allows you to scale arrow tips without changing the line widths or resorting to decorations, you can write

\draw [dashed, -latex new, arrow head=3mm, hvvh/ratio=0.7] (A) |-| (B);

to get

\documentclass[tikz,border=5mm]{standalone}
\usetikzlibrary{paths.ortho, arrows.new}
\begin{document}
\begin{tikzpicture}
\node [draw] (A) {Node A};
\node [draw] (B) at (-1,-2) {Node B};
\draw [dashed, -latex new, arrow head=3mm, hvvh/ratio=0.7] (A) |-| (B);
\end{tikzpicture}
\end{document}

Answer 2

General points can be computed using the calc library of tikz. An expression of the form

($x!t!y$)

will find the point a fraction t along the line from x to y. Combining this with drawing directives |- and -| for "vertical then horizontal" and vice versa gives:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}
  \node[rectangle,fill=blue!30,draw] (A) at (6,4) {Node 1};
  \node[rectangle,fill=blue!30,draw] (B) at (0,0) {Node 2};
  \draw[dashed,->] (A.south) |- ($(A)!.7!(B)$) -| (B.north);
\end{tikzpicture}

\end{document}

There are different ways to change the arrow. Firstly, just writing

\draw[dashed,->,>=stealth]

will give another shape. Loading the tikz library arrows gives plenty to choose between. Making the line thicker will also make the arrow more prominent, e.g. the combination

\draw[dashed,->,>=stealth,very thick]

Note that you could start your picture with \begin{tikzpicture}[>=stealth,very thick] to make all arrowheads of stealth type, and all lines very thick.

For more control over the arrow, you can use the decorations mechanism. In your case this could look like:

from the following code

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{calc,arrows,decorations.markings}

\begin{document}

\begin{tikzpicture}[>=stealth,decoration={markings,mark=at position 1 with
  {\arrow[scale=3]{>}}}]
  \node[rectangle,fill=blue!30,draw] (A) at (6,4) {Node 1};
  \node[rectangle,fill=blue!30,draw] (B) at (0,0) {Node 2};
  \draw[dashed,postaction={decorate}] 
  (A.south) |- ($(A)!.7!(B)$) -| (B.north);
\end{tikzpicture}

\end{document}

See the pgf manual for further details and constructions. Another illustration of arrow tips via decorations may be found at TikZ: Large arrow tips at the end of smooth curves.