Coordinate scale: `dbuPerMicron` and `dbuPerEditorUnit`

How integer DBU in Block geometry map to layout microns and schematic editor units

Two scale fields on CellContent

Field	Used for	Typical value
`dbuPerMicron`	Layout views (GDS, OAS). Physical size: how many integer DBU equal one micron.	`1000` (GDS UNITS record)
`dbuPerEditorUnit`	Schematic / symbol views. How many integer DBU equal `1.0` native editor coordinate in the source tool file.	`1` (Qucs), `1000` (Xschem)

All coordinates in Point, Instance::transform(), wire paths, and pin positions are stored as signed integer DBU in ROOM. Exporters divide by the appropriate scale; importers multiply. Grid snap (Grid=10,10 in Qucs, SNAP in Xschem) stays in editor metadata — it is not the same as DBU scale.

Conversion (schematic / symbol)

// utils/coord_scale.h
DBU       = round(editor_coord × dbuPerEditorUnit)
editor_coord = DBU / dbuPerEditorUnit

effectiveDbuPerEditorUnit(content)  // uses stored value, or infers from SourceInfo::format()

Per-tool defaults

Importer	`dbuPerEditorUnit`	`SourceInfo::format()`	Example
QucsImporter	`1`	`qucs`	`.sch` coord `270` → DBU `270`
XschemImporter	`1000`	`xschem`	`.sch` coord `270.5` → DBU `270500`
GdsImporter	n/a	layout	Uses `dbuPerMicron` from GDS UNITS

On disk (`schema/database.capnp`)

struct CellContent {
  viewType         @0 :ViewType;
  dbuPerMicron     @1 :Float64;
  properties       @2 :List(Property);
  payload          @3 :ViewPayload;
  dbuPerEditorUnit @4 :Float64;  // 0 = infer on read (legacy files)
}

Migration

Older .room files may have dbuPerEditorUnit = 0 (unset). Readers call effectiveDbuPerEditorUnit(): qucs → 1, xschem → 1000. Re-import from the native tool to persist the field explicitly. TextDumper prints both scales per view.

Orientation helpers

coord_scale.h also provides Qucs/Xschem placement mapping used during cross-tool export:

Function	Purpose
`orientToQucsPlacement` / `orientFromQucsPlacement`	Map `Orient` ↔ Qucs mirror/rotate fields
`orientFromQucsLibToNativePdk`	Qucs LibComp E–W ports → native PDK N–S symbols
`qucsLibNeedsEwToNsCompensate`	Detect IHP LibComp vs native symbol orientation mismatch

Wire endpoint alignment uses pin_retarget on top of these scales.

Qucs ↔ ROOM ↔ Xschem

A Qucs schematic opened in Xschem goes through ROOM export (XschemExporter / xschem_bridge). Qucs component types are mapped to Xschem symbols (e.g. GND → gnd.sym; PDK cells resolve via PrimitiveResolver). Coordinates use the view's dbuPerEditorUnit, so Qucs DBU and Xschem editor units stay consistent without ad-hoc divisors.

Coordinate scale: dbuPerMicron and dbuPerEditorUnit