Autolayout specification

Purpose

This package computes positional information for nodes and arcs of a directed graph.  It encapsulates a layout algorithm which is designed to minimize the number of crossing arcs and to emphasize the primary direction of arc flow through the graph.

Effects

  • The expected usage is:
1Call Define for each node and arc to define the graph.
2Call Layout to assign positions to all nodes and arcs.
3Call Position_Of for each node and arc to determine the assigned coordinate positions.
  • Layout can be called multiple times, and recomputes the positions of all currently defined nodes and arcs each time.
  • Once a node or arc has been defined, it remains defined until Clear is called to delete all nodes and arcs.

Performance

This package has been optimized for time, in preference to space.  Layout times are on the order of N*log(N) where N is the number of nodes, but memory space is used inefficiently.

Summary
Autolayout specification
This package computes positional information for nodes and arcs of a directed graph.
Functions
Define
This procedure defines one node of the current graph.
Layout
This procedure assigns coordinate positions to all defined nodes and arcs.
Position_Of
This function returns the coordinate position of the specified node.

Functions

Define

procedure Define (New_Node : in Node)

Purpose

This procedure defines one node of the current graph.

Exceptions

Node_Already_Defined

Layout

procedure Layout

Purpose

This procedure assigns coordinate positions to all defined nodes and arcs.

Exceptions

None.

Position_Of

function Position_Of (Current : in Node) return Position

Purpose

This function returns the coordinate position of the specified node.  The default position (0,0) is returned if no position has been assigned yet.

Exceptions

Node_Not_Defined

procedure Define (New_Node : in Node)
This procedure defines one node of the current graph.
procedure Layout
This procedure assigns coordinate positions to all defined nodes and arcs.
function Position_Of (Current : in Node) return Position
This function returns the coordinate position of the specified node.