Links Between Boxes

Link primitives describe connection geometry without producing SVG path data.

In this package, linking boxes means:

1. choose where a connection leaves one rectangle;
2. choose where it enters another rectangle;
3. compute the intermediate points of the line;
4. expose helper points for labels and arrowheads.

It is the geometry behind any arrow, relation, or connector drawn between two boxes.

Ports

Port::on($rect, PortSide::Right) returns a point on a rectangle edge plus its side.

Sides:

• Top
• Right
• Bottom
• Left

Orthogonal Links

The connector chooses sides from the relative centers of the two rectangles and returns one of three shapes: a straight segment when the boxes line up, an L when they do not, or a Z when the approach has to cross back.

use Atelier\Layout\Geometry\Rect;
use Atelier\Layout\Geometry\RectIndex;
use Atelier\Layout\Geometry\Size;
use Atelier\Layout\Connection\OrthogonalConnector;
use Atelier\Layout\Connection\ConnectionLabel;
use Atelier\Layout\Connection\ConnectionLabelPlacement;

$from = new Rect(20, 20, 80, 40);
$to = new Rect(180, 60, 90, 40);

$connection = (new OrthogonalConnector())->connect($from, $to);

$connection->points;
$connection->segments;
$connection->labelPoint;
$connection->tipTangent;
$connection->isStraight();

$label = ConnectionLabel::for($connection)
    ->size(new Size(20, 10))
    ->avoid(RectIndex::from(['node.a' => $from]))
    ->placement(ConnectionLabelPlacement::Centered)
    ->place();

For the example above, the connection leaves the right side of $from, enters the left side of $to, and may return points like:

100,40 -> 140,40 -> 140,80 -> 180,80

A renderer can turn those points into SVG path data:

M 100 40 L 140 40 L 140 80 L 180 80

labelPoint is the suggested midpoint for an edge label. tipTangent is the final direction vector, useful for drawing an arrowhead at the target.

segments exposes immutable straight pieces with stable indices and axes, so consumers can reason about the first leg, the middle turn, or the final approach without scanning the point list again.

Labels

ConnectionLabel turns a connection plus a measured label size into a deterministic label frame, anchor point, and chosen segment index. It is still renderer-neutral.

ConnectionLabelPlacement also offers Start and End for labels pinned near one extremity rather than the middle.

If you already have solved rectangles, ConnectionLabel::avoid() skips occupied placements deterministically before falling back to the requested placement. See Geometry for the RectIndex it takes.

What Links Between Boxes Do Not Do

This package does not currently solve:

• graph ranking
• obstacle avoidance
• edge bundling
• self-loop semantics
• label collision avoidance
• arrowhead drawing

Those are still consumer responsibilities. A consumer takes the returned points and turns them into whatever its renderer draws.

Demo

php examples/connections-demo.php

The demo prints the source rect, target rect, connection points, label point, and arrowhead tangent for left-to-right, top-to-bottom, and right-to-left cases.