editor

ADR-0008 — Instance rotation by quarter turns ​

Status: Accepted

Context ​

In the View Editor, a symbol instance must be orientable. A free rotation produces non-integer coordinates and non-orthogonal pipes.

Decision ​

  • Rotation stored as an integer number of quarter turns q ∈ {0, 1, 2, 3} (0°, 90°, 180°, 270°).
  • Pivot: the symbol origin (integer point), not its geometric center.
  • Port exit directions rotate with the instance: N → E → S → W → N for a clockwise quarter turn.

Geometric justification ​

  • A 90° rotation around an integer point maps every integer point to an integer point: (x, y) → (−y, x) after translating to the pivot. The model stays 100% integer (ADR-0003).
  • Pivoting around the center of a w × h box shifts the origin by (w − h) / 2: non-integer as soon as w − h is odd. Hence the origin as pivot.
  • A 90° rotation preserves horizontal and vertical directions: pipes stay orthogonal (ADR-0004).

Consequences ​

  • No free rotation, neither in the View Editor nor on instances.
  • Rotation of shapes inside the Symbol Editor: not covered here.

References ​

ADR-0003, ADR-0004