Vector graphics-based software library
Cairo (stylized as cairo) is an open-source graphics library that provides a vector graphics-based, device-independent API for software developers. It provides primitives for two-dimensional drawing across a number of different backends. Cairo uses hardware acceleration when available.
Software architecture.
Language bindings.
A library written in one programming language may be used in another language if bindings are written; Cairo has a range of bindings for various languages including C++, C# and other CLI languages, Delphi, Eiffel, Fortran, Factor, Harbour, Haskell, Julia, Lua, Perl, PHP, Python, Ruby, Rust, Scheme, Smalltalk and several others like Gambas (Visual Basic like).
Toolkit bindings.
Since Cairo is only a drawing library, it can be quite useful to integrate it with a graphical user interface toolkit.
Available back-ends.
Cairo supports output (including rasterisation) to a number of different back-ends, known as "surfaces" in its code. Back-ends support includes output to the X Window System, via both Xlib and XCB, Win32 GDI, OS X Quartz Compositor, the BeOS API, OS/2, OpenGL contexts (directly and via glitz), local image buffers, PNG files, PDF, PostScript, DirectFB and SVG files.
There are other back-ends in development targeting the graphics APIs OpenVG, Qt, Skia, and Microsoft's Direct2D. The BeOS, OS/2 and DirectFB backends were dropped in 2022.
Drawing model.
The Cairo drawing model relies on a three-layer model.
Any drawing process takes place in three steps:
This constitutes a fundamentally different approach from Scalable Vector Graphics (SVG), which specifies the color of shapes with Cascading Style Sheets (CSS) rules. Whereas Cairo would create a mask of a shape, then make a source for it, and then transfer them onto the surface, an SVG file would simply specify the shape with a codice_2 attribute. That said, the models are not incompatible; many SVG renderers use Cairo for heavy lifting.
Example.
Quite complex "Hello world" graphics can be drawn with the help of Cairo with only a few lines of source code:
Notable usage.
Cairo is popular in the open source community for providing cross-platform support for advanced 2D drawing.
History.
Keith Packard and Carl Worth founded the Cairo project for use in the X Window System. It was originally (until at least 2003) called Xr or Xr/Xc. The name was changed to emphasize the idea of a cross-platform library to access display server, not tied to the X Window System.
The name "Cairo" derives from the original name "Xr", interpreted as the Greek letters chi and rho.
Complex text layout.
Cairo handles Latin and CJK based fonts, but does not directly support complex text layout fonts, which require shaping the glyphs. The Cairo developers recommend using Pango, which provides complex text layout and can integrate with Cairo.
References.
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