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;
• external PNG/JPG/JPEG image references stored as linked files, not embedded raster bytes;
• relative image paths, 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 contextual prompts, command aliases, coordinates, relative coordinates, polar input, direct distances, command history navigation and first-pass autocomplete;
• 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 active v0.8.100+ development plan. The v0.9 stabilization gate is deferred until the expanded v0.8 line is consolidated.

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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 row          active tool, contextual prompt and command input
Status bar           coordinates, snap state, measurements, rendered count and messages

The command row is intentionally compact. The active tool and current prompt are shown next to the command input so the user knows which phase is active without losing drawing space.

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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 and oriented rectangle geometry;
• 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 for import drawing, blocks, symbols, stairs and hatch milestones
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/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	release notes draft for the current v0.9 feature set
docs/release-checklist-v0.9.md	manual release checklist for the v0.9 gate
docs/release-publish-v0.9.md	commands and packaging notes for publishing v0.9
docs/stabilization-v0.9-plan.md	v0.9 release-candidate stabilization plan
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, but the Property Panel does not yet provide a tabular editor for individual vertices. A future vertex table will allow precise X/Y correction for each point.
• 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.
• 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.
• Local user settings: basic local settings exist, but the next step is a more complete startup configuration flow for default grid/snap preferences, recent paths and last-file behavior.

Current stabilization checkpoint

OpenCad2D is currently in the v0.9 stabilization cycle. Recent completed work includes:

• Dimension Styles with built-in Standard, Architectural and Mechanical presets;
• a Dimension Style Manager with live preview based on the same DimensionGeometryBuilder used by real dimensions;
• property-panel dimension style selection through a combo box;
• configurable dimension text and terminator fit rules for short dimensions;
• classic dimension terminators including arrows, triangles, dots, architectural ticks and slash symbols;
• left-readable vertical dimension text according to the current OpenCad2D convention;
• bugfixes for Break Point on full ellipses, TRIM open-polyline endpoint filtering and Offset polyline side detection;
• cleanup of obsolete TRIM highlight helper code and clearer Fillet branch-parameter documentation;
• external raster image references with relative paths, missing-reference workflow, Collect Refs and Image References Manager.

The next planning step is v0.9 scope consolidation: decide which remaining polish items are required before the next public release and which are deferred to v1.0.

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.