OpenCad2D

OpenCad2D is an experimental open-source 2D CAD application built with C#, .NET 8 and Avalonia UI.

The project explores how to build a small but serious 2D CAD system from the ground up, with a clean separation between geometry, document modeling, interaction logic, tools, persistence, export and the graphical user interface.

OpenCad2D is not intended to replace mature CAD applications yet. The current goal is to create a precise, fast, testable and understandable 2D CAD foundation.

A long-running personal project

OpenCad2D is not a disposable AI-generated experiment. Its roots go back more than twenty years, to when I first started writing C# and imagining how a personal 2D CAD system could be built from the ground up.

For a long time, the project existed as separate pieces: geometry experiments, drawing ideas, editing tools, file-format tests, interface prototypes and many small lessons accumulated over years of programming. What changed recently is that AI-assisted development finally made it possible to bring those fragments together, review them, refactor them and turn them into a coherent, tested and working application.

AI is part of the process, but it is not the author of the vision. OpenCad2D remains a human-led project: shaped by long-term interest in CAD, by practical software design choices, by tests, by manual validation and by a clear preference for a precise, understandable and open 2D drafting tool.

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Current status

OpenCad2D currently supports a complete early CAD workflow:

• clean startup from Templates/default.opencad2d.json;
• maximized main window on startup;
• native save/load using .opencad2d.json;
• document-level settings persistence for grid, snap, ortho, polar tracking and current drawing settings;
• local application settings for last opened file metadata, recent files and last open/save/export folders;
• document recovery for partially invalid native files;
• New, Open, Save and Save As;
• SVG, DXF and PDF export, including DXF SPLINE knot-vector output and MTEXT reference width;
• ASCII DXF import for core 2D entities, layer tables, MTEXT, LWPOLYLINE bulge arcs, ELLIPSE and readable SPLINE entities;
• layers with visibility and locking;
• reusable line formats with color, lineweight, line style and custom dash pattern values;
• reusable text formats;
• reusable drawing library snippets loaded from library/**/*.opencad2d.json, grouped by category, previewed and inserted as block references, with a first static content pack under library/;
• Blocks v2 manager slices: direct/nested/total reference counts, selected diagnostics, missing-reference diagnostics, recursive-reference blocking, safe duplicate/delete/purge, hardened Edit Block session scope, deterministic Library/block conflict handling and rename closeout with pending rename/reset behavior;
• shared 9-point anchor foundation in the core model, ready for upcoming parametric doors/windows, Library/block insertion refinements and annotation callouts;
• external PNG/JPG/JPEG image references stored as linked files, not embedded raster bytes;
• relative image paths, transparency percentages, missing-image warnings, relink/replace/reset-aspect workflows, Collect Refs packaging and Image References Manager;
• Layer Manager, Line Format Manager, Text Format Manager and Image References Manager;
• compact ColorPicker support in line/text format managers;
• editable Property Panel for supported entities, including MTEXT value/reference-width editing and read-only draw order display;
• independent draw order / Z-order, separate from layers;
• CAD-style command input with a dynamic cursor-adjacent command HUD, contextual prompts, editable numeric fields, command aliases, coordinates, relative coordinates, polar input, direct distances, command history navigation and first-pass autocomplete; the old fixed bottom command row has been removed;
• object snapping, grid snapping, Ortho mode and Polar Tracking;
• selection, Select All, Select Last and Deselect;
• drawing tools for points, single-line text, multiline text, lines, rectangles, circles, ellipses, arcs, polylines, polygons and Bezier splines;
• dimension tools for horizontal, vertical, aligned, radius, diameter and angular dimensions, with stale-state marking after geometry modifications;
• transform tools: move, copy, rotate, scale and point-based align;
• modify tools: delete, break point, break segment, trim, extend, offset, fillet, explode and join;
• trim and break support based on native curve parameters for lines, arcs, circles where applicable, ellipses, elliptical arcs, polylines, polygons and open Bezier splines;
• offset for lines, circles, arcs and straight-segment polylines;
• line-line fillet with radius option, live preview, Trim/NoTrim modes and radius 0 sharp-corner join in Trim mode;
• align object tools: left, right, top and bottom;
• distribute object tools: horizontal and vertical distribution by centers;
• measure tools for distance, entity properties, angles and closed-polyline areas;
• Zoom Window, Zoom Extents, pan and reset view;
• CAD-style crosshair cursor;
• undo/redo for document mutations;
• tool-provided preview descriptor/entity protocols that keep active tool preview logic out of the app renderer;
• minimal application logging for tool/UI exceptions.

See docs/roadmap.md, docs/roadmap-v0.8.100.md and the milestone specifications in docs/specs/ for the reconciled active v0.8 development plan. The planning specification pass defines shared contracts for anchors, leaders/arrows, preview/commit/grouped undo and wall masks. v0.8.180A turned the 9-point anchor contract into a tested core service, v0.8.180B added the reusable HUD 3x3 selector foundation, v0.8.180C introduced the first persistent DoorEntity, v0.8.180D added the first non-destructive wall-opening mask for doors, v0.8.180E introduced the first persistent WindowEntity, v0.8.180F made doors/windows editable from the Property Panel while adding per-command insertion defaults, v0.8.180G closed the first HUD usability loop by showing anchor, mask and door swing state directly in the insertion prompt, and v0.8.180H now closes the first door/window phase as a documentation/validation gate. Existing block and static Library insertion semantics remain unchanged: they use the creation/origin base point, not the 9-point anchor selector. The v0.9 stabilization gate is deferred until the v0.8.160+ Library, compatibility and manual validation pass is complete.

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User interface

The UI is organized into stable zones:

File command bar     New / Open / Save / Save As / export buttons / file name / dirty marker
Top CAD bar          layer selector, layer state, managers, grid, polar tracking, undo/redo, view commands
Left tool panel      Select, Draw, Dimension, Measure, Edit, Order, Align/Distribute and Navigate groups
Center canvas        drawing area with CAD crosshair and previews
Right panel          editable Property Panel
Bottom snap bar      snap toggles and drafting toggles
Command HUD          cursor-adjacent active tool, contextual prompt, options and editable numeric fields
Status bar           coordinates, snap state, measurements, rendered count and messages

The former bottom command row has been replaced by a dynamic cursor-adjacent command HUD. Command aliases, option shortcuts and numeric point entry remain available through the HUD/internal keyboard buffer.

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Command input

OpenCad2D includes a CAD-style guided command input.

Examples:

L
100,100
@100,0

PL
0,0
@100,0
@100<90
C

Supported input forms:

Input	Meaning
100,50	absolute point
@50,0	relative cartesian point
@100<45	relative polar point
25	distance, angle or factor when the active command expects it
C, Close, U, Undo, All, Radius	command options when exposed by the active prompt
empty Enter while idle	repeat the last valid command
empty Enter/right-click inside a command	confirm only if the current phase accepts confirmation
↑ / ↓	navigate command history while the command input is focused
Tab	accept the first autocomplete suggestion for known commands/aliases

Mouse input and typed input feed the same tool state machine. When a tool asks for a point, the user can either click on the canvas or type coordinates.

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Native file format

OpenCad2D saves native drawings as:

.opencad2d.json

The native file stores:

• entities;
• layers;
• line formats;
• text formats;
• dimension styles;
• external image reference paths, oriented rectangle geometry and opacity;
• viewport state;
• document-level settings such as grid, snap, ortho and polar tracking.

The native format is for OpenCad2D save/reopen reliability. Use DXF/SVG/PDF for interchange/export.

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Build and test

dotnet build OpenCad2D.sln
dotnet test OpenCad2D.sln --no-build

Or use the repository workflow:

make check

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Documentation

Important documents:

Document	Purpose
docs/architecture.md	project structure and dependency rules
docs/roadmap.md	current roadmap, completed stabilization work and next milestones
docs/roadmap-v0.8.100.md	extended v0.8.100+ roadmap before the next stabilization gate
docs/specs/	detailed specifications and shared contracts for import drawing, blocks, dynamic command HUD, symbols, stairs, hatch, arrays, doors/windows, annotation markers, UI customization and icon SVG workflow milestones
docs/testing/dynamic-command-hud-manual-verification-2026-05-31.md	manual verification notes for the stabilized HUD and block workflows
docs/commands.md	commands, aliases and undoable command rules
docs/curve-editing.md	Trim/Break curve-editing architecture, native precision and shared cut-point rules
docs/command-input.md	command input syntax and tool workflow
docs/tools.md	tool behavior, workflow rules and preview-provider conventions
docs/library-browser.md	reusable .opencad2d.json library item layout, insertion workflow and limitations
docs/line-formats.md	line format and line style pattern rules
docs/application-settings.md	document settings and local settings separation
docs/draw-order.md	Z-order behavior
docs/persistence.md	native file format, recovery rules and external image reference path rules
docs/known-limitations.md	current limitations, including raster image export parity
docs/release-v0.9.md	historical/future release notes draft for the next stabilization gate
docs/release-checklist-v0.9.md	manual release checklist for the future v0.9 stabilization gate
docs/release-publish-v0.9.md	commands and packaging notes for the future v0.9 publish workflow
docs/stabilization-v0.9-plan.md	future v0.9 release-candidate stabilization plan, deferred until v0.8.160+ consolidation is complete
docs/ai-handoff.md	current handoff for future development

Historical milestone details are intentionally kept out of the active roadmap; use Git history and release notes for old implementation logs.

Current limitations and planned improvements

OpenCad2D is intentionally transparent about what is already solid and what still needs refinement.

• Polyline numeric editing: polylines can be edited visually through canvas grips and segment bulge rows, but a dedicated vertex/segment editor would still be clearer for complex corrections.
• Non-associative dimensions: dimensions store their own measured points and dimension-line geometry. When the measured entity is later moved, scaled or edited, the dimension value does not update automatically. OpenCad2D can mark dimensions as potentially stale after geometry changes, but users must update or recreate them manually.
• Boundary Fill versus HatchEntity: Boundary Fill v2 is implemented for previewed filled-polyline creation, including curve sampling and small-gap bridging. Holes, islands, hatch patterns and associative hatch behavior remain future HatchEntity work.
• External raster image export parity: PNG/JPG/JPEG references are saved, rendered, snapped, transformed and exported to SVG as external links. DXF/PDF raster-image output is still deferred, so those exports currently omit raster content.
• Architectural parametric objects: straight stairs exist as persistent parametric entities. Doors and windows now have first persistent parametric entities with 9-point anchor control. Doors and windows both support the non-destructive wall-opening mask contract.
• Arrays and annotations: AutoCAD-style ARRAYRECT, ARRAYPOLAR, ARRAYPATH, richer arrow tools, section labels and coordinate callouts are planned but not implemented yet.
• UI customization and icons: the current UI is fixed. Future work will add icon-only mode, saved panel/workspace preferences and an SVG export/import workflow for replacing tool icons.

Current stabilization checkpoint

OpenCad2D is currently in the reconciled v0.8 consolidation line. Recent completed work includes:

• Dynamic Command HUD replacing the old fixed command row;
• Import Drawing and Blocks v1;
• Library Browser for .opencad2d.json snippets inserted as block references, now backed by a first small static Library pack;
• parametric straight StairEntity with plan/side/front generated linework;
• Boundary Fill v2 with preview/confirm, curve sampling, editable Gap HUD prompt and endpoint-to-endpoint/endpoint-to-segment gap bridges;
• external raster image references with relative paths, missing-reference workflow, transparency, Collect Refs and Image References Manager;
• mixed-polyline/bulge stabilization and curve-editing fixes;
• SmartPoint Tracking foundation.

The next validation step is to run the local build/test suite and the v0.8.170E Block Manager rename closeout checklist, keeping the v0.8.170A inventory, v0.8.170B duplicate/purge, v0.8.170C edit-session and v0.8.170D Library/block conflict checklists as regression passes. After that, finish the broader v0.8.162 manual compatibility pass before opening doors/windows, arrays, HatchEntity, annotation markers, UI customization or SVG icon workflow.

Info files

Language	Files	Code	Comments	Blank	Total
C#	625	81845	1750	18257	101852
CSS	4	1138	18	40	1196
XML/XAML	16	286	0	64	350
HTML	2	2	0	0	2
Total	647	83271	1768	18361	103400

Metrics

• Comment ratio: 1.71 %
• Blank ratio: 17.76 %
• Code ratio: 80.53 %
• Average lines/file: 159.81
• Largest file: E:\sviluppo\2026 OpenCad2D\src\OpenCad2D.App\ViewModels\MainWindowViewModel.cs (2246 lines)

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License

OpenCad2D is released under the GPL-3.0-or-later license. See LICENSE.

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Credits

Created by Emilie Rollandin.

Current development checkpoint

The current line includes v0.8.180H. The first door/window vertical slice is closed for implementation scope: door and window entities now share the 9-point HUD anchor selector, non-destructive wall-mask behavior, editable Property Panel parameters, per-command insertion defaults for their core dimensions and explicit HUD prompt state for anchor/mask/swing before insertion. The next step is validation through the dedicated v0.8.180H checklist and the broader v0.8.162 compatibility pass, not additional door/window expansion.