Cairo (graphics)-The Daily Ledger

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 back ends. 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).

Cairo (graphics)

Toolkit bindings

Since Cairo is only a drawing library, it can be quite useful to integrate it with a graphical user interface toolkit.

Cairo (graphics)

FLTK has full Cairo support (through --enable-cairo compile switch). GTK began in 2005, with version 2.8, to use Cairo to render the majority of its graphical control elements, and since version 3.0 all rendering is done through Cairo. The Cairo development team maintains up-to-date instructions for rendering surfaces to SDL.

Cairo (graphics)

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: First a mask is created, which includes one or more vector primitives or forms, i.e., circles, squares, TrueType fonts, Bézier curves, etc. Then source must be defined, which may be a color, a color gradient, a bitmap or some vector graphics, and from the painted parts of this source a die cut is made with the help of the above defined mask. Finally the result is transferred to the destination or surface, which is provided by the back-end for the output.

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 style attribute. That said, the models are not incompatible; many SVG renderers use Cairo for heavy lifting.