fix(ConnectorShape): ignore unset arrows in edge bounding box - #1094

PR Checklist

• Addresses an existing open issue: closes #<the_issue_number_here>. If not, explain why (minor changes, etc.).
• You have discussed this issue with the maintainers of maxGraph, and you are assigned to the issue.
• The scope of the PR is sufficiently narrow to be examined in a single session.
• I have added tests to prove my fix is effective or my feature works.
• I have provided screenshot/videos to demonstrate the change. Not relevant: the change only affects the computed bounding box dimensions, it has no visual rendering output of its own; it is covered by automatic tests.
• I have added or edited necessary documentation, or no docs changes are needed.
• The PR title follows the "Conventional Commits" guidelines.

Overview

ConnectorShape.augmentBoundingBox treated an unset startArrow/endArrow as present, so an edge with no arrow on a side still grew its bounding box by an extra marker size on that side.

The check was a strict comparison against NONE:

if (this.style.startArrow !== NONE) { ... }

When the style does not define the arrow, this.style.startArrow is undefined, and undefined !== 'none' is true, so the branch runs for arrows that were never set. This grows the bounding box (and therefore the graph bounds and the computed fit scale) more than it should.

This is a porting regression from mxGraph. mxConnector.augmentBoundingBox reads the arrow with getValue(style, ARROW, NONE), which defaults an absent key to NONE, so the branch is correctly skipped.

The fix defaults the value before comparing, mirroring mxGraph and aligning with createMarker in the same file which already uses ... || NONE:

if ((this.style.startArrow ?? NONE) !== NONE) { ... }
if ((this.style.endArrow ?? NONE) !== NONE) { ... }

Tests: data-driven coverage was added on augmentBoundingBox for the cases only end arrow set, only start arrow set, no arrow set, explicit none on both sides, and both arrows set. The first three were red before the fix.

Notes

While investigating this, it became clear that the mxGraph to maxGraph migration introduced regressions in several places where a style default value is not handled the way mxGraph handled it (mxGraph systematically went through getValue(style, KEY, default), whereas maxGraph sometimes reads the property directly and compares it without applying the default). Several such cases have already been fixed individually, but we will need to conduct a general investigation to systematically compare the default values used in mxGraph and maxGraph, to catch the remaining occurrences rather than fixing them one by one as they are discovered.

Summary by CodeRabbit

• Bug Fixes

  • Fixed incorrect bounding box calculations for connector shapes when arrow styles are undefined or set to none.

• Tests

  • Added test coverage for connector shape bounding box behavior with various arrow configurations.