ofxDxf

Load, display, and save 2D DXF geometry for openFrameworks plotting and conversion workflows.

Built on dxflib. Geometry uses a dual storage model:

• ofPath — exact commands where openFrameworks supports them: lines, circular arcs, circles, bulge arcs (path.arc / path.circle).
• Metadata — DxfArcInfo, DxfEllipseInfo, DxfSplineInfo when DXF needs extra fields. Ellipse/spline entities keep path empty; preview tessellates from metadata at draw time.

Native CIRCLE / ARC store both metadata and a synced exact ofPath. Display tessellation follows ofGetStyle() and view zoom.

Load is lossless and non-destructive — no heuristic curve fitting runs automatically. Optional promoteCurves() can recover bulge arcs or (if you opt in) faceted circles later.

Examples

Example	Description
example-simple	Minimal DXF viewer (drag & drop)
example-dxftosvg	DXF ↔ SVG converter with layer UI and export

Basic usage

#include "ofxDxf.h"

DxfDocument doc = ofxDxf::load("drawing.dxf");
if (doc.empty()) return;

for (auto& err : doc.errors)   // includes skip summary when present
    ofLogWarning("ofxDxf") << err;

DxfViewContext view;
view.center    = viewCenter;      // world-space pan
view.viewportW = ofGetWidth();
view.viewportH = ofGetHeight();

for (auto& layer : doc.layers) {
    for (auto& entity : layer.entities) {
        entity.draw(zoom, -1, &view);  // preview — local arc tessellation
        // entity.exportPath();        // plot / SVG — exact where possible
    }
}

ofxDxf::save(doc, "out.dxf");       // R2000 ASCII DXF
doc.flipY();                         // DXF Y-up ↔ screen Y-down

Supported on load

Feature	Status	Notes
LINE	✅	Native ofPath
ARC	✅	Exact arc commands + DxfArcInfo
CIRCLE	✅	Exact arc / circle + DxfArcInfo
LWPOLYLINE	✅	Lines + bulge arcs
POLYLINE	✅	Legacy polyline + vertices
ELLIPSE	✅	Metadata preserved; display via tessellation
SPLINE	✅	NURBS metadata preserved; display via tessellation
POINT	✅	Loaded; not drawn by default
INSERT / BLOCK	✅	Blocks collected; INSERT expanded (scale, rotation, arrays); block entity layers preserved
Deferred INSERT	✅	INSERT before block definition — resolved after load
HATCH	✅	Boundary edges as typed entities (line / arc / ellipse / spline / bulge polyline); fill pattern ignored
SOLID / TRACE / 3DFACE	✅	Closed polylines (≤4 corners)
Layers	✅	LAYER table + entity layer attribute
Colors	✅	ACI palette + 24-bit color24
Empty layers	✅	Layers from table appear even with 0 entities
Skip diagnostics	✅	Counts ignored types; logged + appended to doc.errors

Export / save (ofxDxf::save)

Entity	Write format
Line, arc, circle	Native DXF entities (from arcInfo when present)
Ellipse, spline	Native DXF when metadata present
Hatch / solid / trace	Native types when metadata present; else LWPOLYLINE
Other / fallback	LWPOLYLINE at export quality (exportPath())

INSERT/BLOCK structure is not recreated on save — output is flat geometry.

Preview rendering

Circles and arcs tessellate at arc center in local coordinates (avoids jitter on large sheet coordinates). Rules:

Source	Preview path
Native CIRCLE / ARC (arcInfo)	Local tessellation from DxfArcInfo
ELLIPSE (ellipseInfo)	Local tessellation at ellipse center (zoom-adaptive)
SPLINE (splineInfo)	Local NURBS tessellation at spline centroid (zoom-adaptive)
Bulge polylines (ofPath arc commands)	Each arc drawn locally; elliptical arcs when radiusX ≠ radiusY
Chord-faceted polylines (many lineTo)	Drawn as stored — call promoteCurves() to recover arcs/circles

Pass DxfViewContext to entity.draw() so full circles only stroke the viewport-visible arc span at high zoom.

Optional curve promotion

Heuristic fitting never runs on load. Call explicitly when you want polylines replaced by native CIRCLE / ARC metadata:

DxfCurvePromotionSettings settings;
settings.promoteBulgeArcCircles = true;   // exact: arc commands spanning 360°
settings.promoteBulgeArcs       = true;   // exact: single bulge arc
settings.promoteFacetedCircles  = false;  // off by default — avoids hexagon → circle
settings.promoteFacetedArcs     = false;  // off by default — open chord arc → ARC

auto result = ofxDxf::promoteCurves(doc, settings);
// result.circlesPromoted, result.arcsPromoted, result.entitiesExamined

Setting	Default	Meaning
promoteBulgeArcCircles	true	Closed loop of exact arc commands → CIRCLE
promoteBulgeArcs	true	moveTo + one arc (bulge) → ARC
promoteFacetedCircles	false	Chord-fit closed polyline → CIRCLE (heuristic)
promoteFacetedArcs	false	Chord-fit open polyline → ARC (heuristic)
facetedCircleMinVertices	16	Minimum facet count for closed circle fit
facetedArcMinVertices	8	Minimum facet count for open arc fit
facetedCircleMaxRelativeError	0.01	Max radius fit error
facetedCircleMaxEdgeVariance	0.05	Rejects uneven edge lengths (circles only)

Promotion preserves layer, color, and other entity metadata. Entities that already have arcInfo are never changed.

INSERT transforms

• Uniform block scale: arcInfo and path stay in sync after INSERT (CIRCLE / ARC).
• Non-uniform scale on circles/arcs: converted to DxfEllipseInfo (Type::Ellipse) so export writes native DXF ELLIPSE, not a false circle or tessellated polyline fallback.

Not supported (counted & logged)

These are parsed by dxflib but not converted to geometry. Counts appear in the console and in doc.errors (e.g. Skipped/unresolved: TEXT=12 DIMENSION=4):

Type	Common in
TEXT / MTEXT	Labels, part numbers
DIMENSION (+ variants)	AutoCAD dimensions
HATCH fill pattern	Pattern fill (boundaries are loaded)
XLINE / RAY	Construction geometry
ATTRIB	Block attribute text
IMAGE	Raster references
LEADER	Annotation leaders
Paper space layouts	Layout tabs (model space only)
Linetypes / lineweights	Stored in DXF; not applied on draw
Unknown INSERT	Block name not found after deferred retry

If geometry is missing, check the console ofxDxf: Load summary line or doc.errors.

Geometry API

Method	Use
entity.path	Exact ofPath when geometry allows (lines, arcs, bulge); empty for ellipse/spline
entity.arcInfo	Native circle/arc parameters (export source of truth)
entity.exportPath()	Export / plot — exact paths; arcInfo rebuilt into ofPath
entity.resolvedPath()	Display — uses ofGetStyle() segment count
entity.getOutline()	Tessellated polylines (local arc tessellation when arcInfo present)
entity.draw(zoom, segs, &view)	Preview with zoom-adaptive local arcs
ofxDxf::promoteCurves(doc, settings)	Optional in-place CIRCLE/ARC recovery

Tessellation resolution is not stored on the document — it comes from render context (ofGetStyle(), zoom), except export which uses world-space quality automatically for splines/ellipses.

Roadmap (next improvements)

Item	Effort	Notes
Linetype on draw	medium	Dashed layer styles
DIMENSION → lines/arcs	~1 day	Explode dimension primitives
TEXT outline / bbox	~1–2 days	Optional labels for reference
Paper space	medium	Layout tab support
INSERT/BLOCK on save	medium	Preserve block structure round-trip
Full HATCH fill	high	Pattern rendering, not just boundaries

Dependencies

• openFrameworks (ofPath, ofPolyline, …)
• dxflib (included under libs/dxflib)

Optional in examples: ofxSvg, ofxImGui, ofxImGuiStyle.

License

See addon and dxflib license files.