canvas
A Go vector graphics library that renders to SVG, PDF, raster images, HTML Canvas, and more with advanced text and path operations.
What is canvas?
Canvas is a vector graphics library written in Go that provides a unified API for rendering to multiple formats including SVG, PDF, raster images, and HTML Canvas. It solves the problem of generating high-quality vector graphics with advanced text layout and precise path operations in Go applications.
Go developers needing to generate vector graphics, PDFs, or complex text layouts, such as those building charting libraries, document generators, or graphics-intensive applications.
Developers choose Canvas for its numerically stable path operations, multi-format output from a single API, and production-ready performance with optimized rasterization, making it a robust alternative to C-based libraries like Cairo.
Overview
Vector graphics in Go
Use Cases
Best For
- Generating PDF reports with complex text layouts and vector graphics in Go
- Creating SVG or raster images from vector paths with precise dashing and stroking
- Building charting or plotting libraries that require high-quality text rendering
- Developing generative art tools that need stable boolean operations on paths
- Rendering maps or GIS data with degenerate geometries and overlapping segments
- Converting LaTeX formulas to vector paths for inclusion in graphics
Not Ideal For
- Real-time interactive applications requiring sub-millisecond rendering latencies, such as video games or live animations
- Projects where binary size must be minimized, due to dependencies on HarfBuzz and FriBidi with potential CGO overhead
- Teams needing extensive, beginner-friendly documentation and tutorials for quick onboarding
- Simple image manipulation tasks that don't require vector graphics or multi-format output
Pros & Cons
Pros
Outputs to SVG, PDF, EPS, raster images, HTML Canvas via WASM, and more from a single API, as shown in the README's feature list and examples like the HTML Canvas demo.
Uses HarfBuzz for shaping, FriBidi for bidirectionality, and Knuth's algorithm for line breaking, supporting mixed scripts and fonts, evidenced by the text formatting examples in Figure 1.
Provides numerically stable boolean operations (AND, OR, XOR, etc.) with O((n+k) log n) complexity, tested extensively with degenerate data like OpenStreetMap shapes.
Features an ASM-optimized rasterizer that benchmarks show is at least twice as fast as alternatives like Cairo in extreme cases, per the README's performance discussion.
Cons
Recent changes in the README, such as renamed methods and parameter adjustments, indicate breaking updates that can disrupt existing codebases.
The author admits the library's vast scope and complexity likely hide bugs, with coverage still lacking despite unit and fuzz tests.
Optimal performance with HarfBuzz and FriBidi requires CGO, which complicates cross-compilation and adds external dependencies.
Open Source Alternative To
canvas is an open-source alternative to the following products:
node-canvas is a Cairo-backed Canvas implementation for Node.js that allows server-side generation of images and graphics using the HTML5 Canvas API.
Cairo is a 2D graphics library that provides vector drawing capabilities with support for multiple output targets including screen, PDF, and SVG.
Frequently Asked Questions
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