forked from 1b-agent/opencadstudio-upstream
75 lines
3.7 KiB
Markdown
75 lines
3.7 KiB
Markdown
# Dimensions through layout viewports
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In paper space, snap to model geometry displayed through a planar, orthographic
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viewport. `DIMLINEAR`, `DIMALIGNED`, `DIMANGULAR`, `DIMRADIUS`, and `DIMDIAMETER`
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also support their usual object-pick modes through these viewports.
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## Measurement
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- Model geometry supplies the viewport scale. A 100-unit model length displayed
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at 1:10 measures 100, although it occupies 10 paper units.
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- A paper-space centerline or free sheet point can be combined with model
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geometry through one viewport, in either pick order. The paper-space span is
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measured using that viewport's scale.
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- Sheet-only dimensions measure paper units, even inside a viewport rectangle.
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- Model picks from a second viewport are rejected without advancing the command.
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Dimension-line and text placement do not change the measurement scale.
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- The current dimension style's unit conversion is preserved. Angular dimensions
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do not use length compensation. `DIMASSOC=0` explodes the compensated dimension.
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Snapping and object picking respect visibility, clipping, and viewport draw order.
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Paper geometry has priority in object picks. Ordinary selection uses the active
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drawing space. Object picks reuse the resident interaction index and resolve
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nested block transforms.
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## Saved scale
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Length dimensions store paper-space definition points and a negative `DIMLFAC`
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override: user unit factor multiplied by `1 / viewport scale`.
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`OCS_VIEWPORT_MEASUREMENT` XData stores version `1` (integer16), the positive user
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factor (real), and viewport compensation (real). Keeping the factors separate
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allows compensation to change without losing the user's unit conversion.
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Both the override and XData survive DXF/DWG saves and undo/redo.
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## Associations
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With `DIMASSOC=2`, acquired features retain their viewport, block-instance path,
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source entity, and snap feature. Intersections retain both source chains.
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Source edits and viewport changes update the dimension and its compensation,
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preserving style overrides and user-positioned text on the sheet.
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A sheet centerline stays on the sheet; a model endpoint follows its viewport.
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Moving the viewport therefore changes the distance between them. Undo/redo and
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DXF/DWG saves preserve the references.
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Properties shows association status. If a required reference is broken or cannot
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be resolved, the entire dimension keeps its last valid geometry and reference
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records. A successful refresh regenerates its displayed and exported geometry.
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## Limits
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Unsupported cases preserve saved dimensions:
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- Perspective or oblique views; missing or malformed reference chains.
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- Array instances without an addressable instance index, nesting beyond eight
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levels, and radial measurements of nonuniformly scaled circles or arcs.
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- Intersections without two identifiable source chains inside a batched block.
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- Ambiguous imported endpoint, midpoint, or quadrant markers. A stored point can
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validate a feature; it cannot establish an otherwise unknown identity.
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- Tangency without a verified solution, or two perpendicular/tangent references
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requiring a coupled solve.
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- Imported viewport scaling without OCS scale metadata or
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`ACAD_DIMASSOC_CALC_DIMLFAC` identifying the saved compensation.
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## Tests
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Run `cargo test --locked --lib viewport_dimension`. Tests cover the five commands,
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mixed sheet/model input, styles, clipping, object picks, source/viewport edits,
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snap features, nested paths, intersections, preserved overrides, undo/redo, and
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DXF/DWG persistence. The synthetic association fixture is in
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`tests/fixtures/dim_assoc/`.
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