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.

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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;
• Layer Manager, Line Format Manager and Text Format 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 and Select Last;
• 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 and fillet;
• trim and break support for lines, arcs, circles where applicable, ellipses, polylines, polygons and sampled Bezier splines;
• offset for lines, circles, arcs, straight-segment polylines and sampled Bezier splines, including preview and miter-limit fallback for sharp polyline corners;
• 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/release-v0.8.md for the current release notes.

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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 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;
• 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/commands.md	commands, aliases and undoable command 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 and recovery rules
docs/release-v0.8.md	current release notes
docs/release-v0.8-final.md	GitHub-ready v0.8.x final release draft
docs/stabilization-v0.9-plan.md	v0.9 release-candidate stabilization plan
docs/ai-handoff.md	current handoff for future development

Historical milestone notes before v0.8 are no longer needed in the active documentation set.

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License

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

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Credits

Created with love by Emilie Rollandin.