\return_arrow

Description 

\return_arrow is the second operator to draw arrow associated to fold operations. \return_arrow is design to build a curved arrow often used for mountain fold, or back fold. Arguments of this operator are:

• an edge, beginning of the arrow (in figure $[m_{1}, m_{2}]$),
• an edge, limit of the arrow (in figure $[a, b]$),
• first arrow head type,
• second arrow head type,
• side of the arrow end (left or right),
• arrow length ratio (called $\mathcal{R}$).

Figure: Points to compute a return arrow and result

The type of each arrow head and the side of the arrow should be specified by the same way as in \simple_arrow. Arrow is computed using edges, side and ratio parameters. It is a bezier curve oriented along the line defined as the mediator of $[m_{1}, m_{2}]$ (orthogonal crossing the middle of first edge parameter of the arrow). In example this mediator is called $[o, o_{2}]$. The arrow begins near to the middle of the $[o, o_{2}]$ segment point ($o_{1}$) and ends near to the intersection of $[o, o_{2}]$ and limit arrow edge ($[a, b]$). In example, the end of arrow is close to point $o_{2}$. Length of the arrow along $[o, o_{2}]$ depends of the ratio $\mathcal{R}$ of the arrow beyond $[a, b]$. The default value of $\mathcal{R}$ is 50% so the distance of arrow beyond $[a, b]$ is equal to the distance between the begin of arrow and point $o_{2}$. The side parameter allows to specify whether the arrow is drawn at left or right of $[o, o_{2}]$.
This operator should only appear within a step block.

Usage

  % balanced return arrow
  \return_arrow([mid_ad, mid_bc], [a, b], none, mountain, left);
  % long return arrow (3/4 beyong [a, b])
  \return_arrow([mid_ad, mid_bc], [a, b], unfold, mountain, right, 75);

Formal structure

  \return_arrow(EDGE_1, EDGE_2, SRC_ARROW, DST_ARROW, SIDE, RATIO);

Parameters

  EDGE_1
  Description    : Indicates the origin of arrow (often fold line).
  Type           : Edge, couple of vertex identifiers.
  Allowed values : Any couple of vertex identifiers already 
                   defined in a previous step.

  EDGE_2
  Description    : Indicates the limit where the arrow returns.
  Type           : Edge, couple of vertex identifiers.
  Allowed values : Any couple of vertex identifiers already 
                   defined in a previous step.

  SRC_ARROW
  Description    : Indicates the type of arrow head at the origin.
  Type           : Arrow head type.
  Allowed values : One value in {valley, mountain, unfold, none}.

  DST_ARROW
  Description    : Indicates the type of arrow head at the end.
  Type           : Arrow head type.
  Allowed values : One value in {valley, mountain, unfold, none}.

  SIDE (optional) 
  Description    : Indicates the orientation side of the arrow.
  Type           : Side type.
  Allowed values : One value in {left, right}.
  Default value  : right

  RATIO (optional) 
  Description    : Indicates the curve ratio of the arrow.
  Type           : Percentage type.
  Allowed values : One value in the range ]0, 100[.
  Default value  : 50.