CAD-Viewer

简体中文

cad-viewer is the first web-based DXF/DWG viewer and editor in the world that operates entirely in browser, without relying on any backend services. By performing DWG/DXF parsing, geometry processing, and rendering directly in the browser, cad-viewer enables true serverless CAD viewing and editing, ideal for cloud apps, offline usage, and privacy-sensitive workflows.

It also offers something you will rarely find in other CAD viewers—one-click export to a single, self-contained HTML file. The downloaded .html embeds the drawing snapshot and a lightweight viewer runtime, so recipients can open, pan, zoom, toggle layers, and measure distances in any modern browser with no CAD app, no server, and no install. Most desktop and web CAD viewers only let you view inside their own product; cad-viewer turns a live drawing into a portable, offline artifact you can email, archive, or drop on a static file host—ideal for sharing with clients, compliance archives, and air-gapped workflows. The offline viewer also uses far less memory than traditional desktop tools when opening the same drawing (see memory comparison below).

• 🌐 Live Demo
• 🌐 API Docs
• 🌐 Wiki
• X (Twitter): @mlightcad
• YouTube: @mlightcad
• Medium: @mlightcad
• Juejin(稀土掘金): @mlightcad

Apps Built with cad-viewer

The Thingraph team builds production DWG/DXF viewers and platform integrations on top of cad-viewer, serving tens of thousands of users worldwide:

• DWG Viewer Web App — Browser-based DWG/DXF viewer used by engineering teams worldwide for fast, serverless drawing access. Install for your platform:
  • Google Drive — open DWG/DXF from Drive with Open with
  • VS Code — custom read-only editor for .dwg / .dxf
  • Cursor — same extension via Open VSX
  • Confluence — embed DWG/DXF previews on pages
  • Windows Explorer — thumbnail and preview in File Explorer

Features

• High-performance viewing of large DWG/DXF files with smooth 60+ FPS rendering
• No backend required - Files are parsed and processed entirely in the browser
• Enhanced data security - Files never leave your device, ensuring complete privacy
• Easy integration - No server setup or backend infrastructure needed
• Modular architecture for seamless third-party integration
• Export to offline HTML — Export the current drawing as one self-contained .html file with an embedded viewer (pan/zoom, zoom extents, layers, distance measure, EN/ZH UI). Opens offline in any browser; no cad-viewer instance or backend required.
• Offline and online editing workflows
• THREE.js 3D rendering engines with advanced optimization techniques
• Designed for extensibility and integration with platforms like CMS, Notion, and WeChat

Getting Started

Prerequisites

• Node.js >= 24
• pnpm >= 10

Installation

git clone https://github.com/mlightcad/cad-viewer.git
cd cad-viewer
pnpm install

Development

# Start the full-featured viewer (cad-viewer)
pnpm dev

# Or start the simple viewer
pnpm dev:simple

Build

pnpm build

Preview

# Preview the full-featured viewer
pnpm preview

# Preview the simple viewer
pnpm preview:simple

How to Use

Desktop Browser Operations

• Select: Left-click on entities
• Zoom in/out: Scroll mouse wheel up/down
• Pan: Hold middle mouse button and drag
• Erase: Select entities and press Del key

Pad/Mobile Browser Operations

• Select: Tap on entities
• Zoom: Pinch with two fingers
• Pan: Single-finger drag

Plugin System

CAD-Viewer is built around a modular plugin system in @mlightcad/cad-simple-viewer. Plugins implement the AcApPlugin interface and hook into viewer lifecycle via onLoad / onUnload—typically to register commands, add UI, or wire export/import pipelines.

Load plugins through AcApDocManager.instance.pluginManager (loadPlugin, registerLazyPlugin, or plugins.fromConfig when creating the document manager). Export-oriented plugins support lazy loading: register a small stub up front and download the heavy bundle only when the user runs the related command (for example -chtml, or when confirming export from the chtml dialog in cad-viewer).

The monorepo ships several first-party plugins. Each focuses on one concern; combine them as needed. Installation, registration, and API details live in each package’s README—see the links below.

Official plugins

Package	Role	Commands / capabilities
@mlightcad/cad-simple-ui-plugin	Toolbar & layer manager UI for cad-simple-viewer (plain DOM, no Vue/React)	layer, default toolbar (view, measure, export, review, theme, locale)
@mlightcad/cad-agent-plugin	Natural-language CAD agent (AI chat panel + drawing tool calls)	agent
@mlightcad/cad-html-plugin	Export drawings to self-contained offline HTML	chtml (dialog in cad-viewer), -chtml (command-line)
@mlightcad/cad-pdf-plugin	PDF export and import (vector pipeline)	cpdf, ipdf
@mlightcad/cad-svg-plugin	SVG export and shared vector renderer (also used by PDF export)	csvg

@mlightcad/cad-simple-ui-plugin — UI chrome for the simple viewer

cad-simple-viewer deliberately ships no application UI—only the canvas and CAD core. If you embed the simple viewer in your own web app and want ready-made chrome without adopting the full Vue-based cad-viewer shell, cad-simple-ui-plugin is the intended UI layer.

It provides:

• A configurable toolbar (placement on any edge, default CAD commands, nested menus, custom items)
• A floating layer manager (layer on/off, ACI color picker, zoom-to-layer on double-click)
• Theme sync with the COLORTHEME sysvar and --ml-ui-* CSS tokens on your host element
• Locale sync with AcApI18n (English / Chinese)

All widgets are framework-agnostic (plain DOM). The full Vue cad-viewer app has its own Element Plus UI and does not require this plugin; use cad-simple-ui-plugin when you build on cad-simple-viewer directly.

→ Quick start, toolbar customization, and options: packages/cad-simple-ui-plugin/README.md

@mlightcad/cad-agent-plugin — AI drawing assistant

cad-agent-plugin adds a natural-language CAD agent to cad-simple-viewer-based apps. Users describe what they want in plain language; the agent calls CAD tools to inspect the drawing and create or modify geometry.

It provides:

• A lazy-loaded AcApPlugin (trigger command: agent) so the AI bundle is not on the critical path
• A Vue chat panel (AgentChatPanel) built on the Vercel AI SDK (Experimental_Agent + @ai-sdk/vue)
• Browser-side LLM configuration — API keys for OpenAI, Anthropic, or OpenAI-compatible endpoints stay in the client (encrypted in localStorage)
• Phase 1 CAD tools — get_drawing_context; draw_line, draw_circle, draw_arc, draw_rectangle, draw_polyline, draw_text; set_current_layer, create_layer, zoom_extents
• English / Chinese UI strings via the plugin i18n layer

The full Vue cad-viewer app registers the agent automatically when the package is installed (palette tab). cad-simple-viewer-example wires it into a dock tab via cad-simple-ui-plugin. Host apps call registerLazyAgentPlugin and setAgentPaletteOpener to mount the panel where they want.

→ Installation, registration, and tool list: packages/cad-agent-plugin/README.md

Export plugins (HTML / PDF / SVG)

These plugins add export (and PDF import) commands to the same plugin manager. They are lazy-loaded so initial page weight stays small. The cad-simple-viewer-example demo registers all three export plugins, cad-simple-ui-plugin, and cad-agent-plugin; the full cad-viewer app registers the export plugins and the agent plugin (when installed) in its bootstrap.

• HTML — one-file offline viewer for sharing and archiving: packages/cad-html-plugin/README.md
  (Headless CLI using the same pipeline: packages/cad-html-exporter-cli/README.md)
• PDF — vector PDF export and PDF-to-CAD import: packages/cad-pdf-plugin/README.md
• SVG — vector SVG export: packages/cad-svg-plugin/README.md

Self-contained HTML memory usage

When opening the sample drawing canteen.dwg, memory consumption is roughly:

Viewer	Memory consumption
AutoCAD 2020	320 MB
GstarCAD Viewer (浩辰看图王)	246 MB
Self-contained HTML (measure mode)	56 MB
Self-contained HTML (view mode)	33 MB

The offline HTML viewer uses about 83% less memory than AutoCAD 2020 and about 77% less than GstarCAD Viewer in view mode, while still supporting pan/zoom, layer toggle, and distance measurement (measure mode).

Performance

CAD-Viewer is engineered for exceptional performance and can handle very large DXF/DWG files while maintaining high frame rates. It employs multiple advanced rendering technologies to optimize performance:

• Custom Shader Materials: Uses GPU-accelerated shader materials to render complex line types and hatch fill patterns efficiently
• Geometry Batching: Merges points, lines, and areas with the same material to dramatically reduce draw calls
• Instanced Rendering: Optimizes rendering of repeated geometries through instancing techniques
• Buffer Geometry Optimization: Efficient memory management and geometry merging for reduced GPU overhead
• Material Caching: Reuses materials across similar entities to minimize state changes
• WebGL Optimization: Leverages modern WebGL features for hardware-accelerated rendering

These optimizations enable CAD-Viewer to smoothly render complex CAD drawings with thousands of entities while maintaining responsive user interactions.

Known Issues

CAD-Viewer has some known limitations that users should be aware of:

• Unsupported Entities:

  • XRefs: External references (XRefs) are not currently supported. This is mainly because file access in the browser works differently from desktop CAD applications. Support for XRefs is planned for a future release.

• DWG File Compatibility:

  • Some DWG drawings may fail to open due to bugs in the underlying LibreDWG library. This is a known limitation of the current DWG parsing implementation. If you find those issues, please log one issue on CAD-Viewer issues page or LibreDWG issues page.
  • Drawings that contain third-party custom entities (e.g., Tianzheng drawings in the Chinese architecture and construction industry) may not display correctly unless proxy graphics are saved. When saving such drawings, ensure the system variable PROXYGRAPHICS is set to 1. If proxy graphics are embedded in the file, CAD-Viewer can display them.

  Whether proxy graphics are written when saving a DWG is controlled by the system variable PROXYGRAPHICS:

  Value	Meaning
  0	Do not save proxy graphics
  1	Save proxy graphics

• DWG File Size Limits:

  • Parsing DWG files with LibreDWG is memory-intensive and can easily exceed 2 GB of RAM. libredwg-web therefore enforces WASM heap memory limits; very large DWG files may fail to parse.
  • We offer a proprietary DWG/DXF parser with significantly lower memory usage, support for larger files, and more accurate parsing. It integrates with the same @mlightcad/data-model as the open-source converters and can replace the GPL-based dxf-json-converter and libredwg-converter stack for closed-source commercial products. See the commercial license document for scope, pricing, GPL compliance, and support terms.

Roadmap

The goal of this project is to create a full-featured 2D AutoCAD-like system in the browser (viewer + editor), with modular architecture and framework-agnostic integration.

Legend:

• Completed
• Planned
• ⏳ In progress

Core File & Data Layer

File Support

• DXF loading
• DWG loading
• Export to self-contained offline HTML (embedded viewer)
• Large file streaming / incremental loading
• ⏳ File version compatibility (R12–Latest)

Data Model

• Unified entity data model
• Layer table support
• Block / insert structure
• ⏳ Handle & object ID management: currently objectId is same as handle and represented as one string instead of bigint (int64).
• ⏳ XData / extension dictionary support
• Proxy entity handling

Rendering & Performance

Rendering Engine

• WebGL-based rendering (Three.js)
• 2D-only optimized pipeline
• Layer-based scene organization
• Layout / paper space rendering
• Viewport entity support

Performance Optimization

• Geometry merging & batching
• Spatial indexing (basic)
• Advanced spatial index (R-tree / BVH)
• Level-of-detail (LOD) rendering
• Multi-canvas / tiled rendering for very large drawings

Viewing & Navigation

View Controls

• Pan
• Zoom (wheel / box zoom)
• Fit to view / extents
• Named views
• View history (undo / redo view changes)

Display Controls

• Layer visibility on/off
• Layer freeze / lock
• Lineweight display
• Linetype scaling
• Background / theme switching

Selection & Interaction

Selection

• Single entity selection
• Highlight selected entities
• Window selection
• Crossing selection
• Selection filters (by type / layer)
• Selection cycling

Snapping (OSNAP)

• Endpoint
• Midpoint
• Center
• Intersection
• Perpendicular / tangent
• Nearest
• Snap tracking

Editing & Modification

Basic Editing

• Entity editing framework
• Move
• Copy
• Rotate
• Scale
• Delete
• Undo / redo

Geometry Editing

• Grip points
• Stretch
• Trim
• Extend
• Offset
• Explode
• Join / fillet / chamfer (2D)

Drawing & Creation Tools

Basic Entities

• Line
• Polyline
• Spline
• Circle
• Arc
• Ellipse
• Rectangle / polygon

Advanced Entities

• Hatch
• Text (single-line / multi-line)
• Dimensions (linear, aligned, angular)
• Blocks creation & insertion

Measurement

• Distance
• Arc length
• Area
• Angle
• Coordinate
• Entity statistics (length, area, count)

Dimension

• Linear dimension
• Angle dimension
• Coordinate

Properties & UI Panels

Property Palette

• Selected entity properties
• Layer, color, linetype editing
• Live update on change

Panels & UI

• Layer manager
• Block manager
• Command history / console
• Status bar (snap, ortho, grid)

Command System

• Command registry
• Command aliases
• Command prompts (AutoCAD-style)

Integration & Extensibility

Framework Integration

• Framework-agnostic core
• React integration example
• Vue integration example
• OpenLayers / Map integration
• CMS / Notion embedding

Plugin System

• Plugin API
• Custom entity support
• Custom command

Offline & Online Editing

Offline Editor

• Local editing in browser
• Save to DXF
• Save change set / diff
• IndexedDB persistence

Online Editor

• Backend API design
• User authentication
• File versioning
• Multi-user access control
• Real-time collaboration (future)

Platform Targets

• ⏳ Google Drive Integration
• WeChat Mini Program viewer
• Mobile browser support (read-only)

Documentation & Community

• Architecture documentation
• API reference
• Contribution guide
• Example projects
• Roadmap & changelog maintenance

This roadmap is intentionally granular so contributors can clearly see what exists, what is missing, and where help is needed.

Contributing

Contributions are welcome! Please open issues or pull requests for bug fixes, new features, or suggestions. For bug reports, providing a link to the problematic drawing will help in reproducing and fixing the issue.

License

The cad-viewer monorepo is primarily MIT licensed.

The default DXF/DWG loading path in @mlightcad/cad-simple-viewer depends on GPL-3.0 packages (dxf-json / @mlightcad/dxf-json-converter for DXF, libredwg-web / @mlightcad/libredwg-converter for DWG). If you ship a closed-source product and cannot distribute GPL code to your customers, use the proprietary DWG/DXF parser instead — it replaces those converters and lets the rest of the stack remain MIT-only.

→ Commercial parser: PROPRIETARY-PARSER.md (scope, licensing, pricing, integration, GPL compliance, support)