Cairo is a 2D graphics library featuring a sophisticated API for drawing vector graphics, compositing images, and rendering anti-aliased text. Cairo provides support for multiple output devices, including the X Window System, Microsoft Windows, and image buffers in memory, allowing you to write platform-independent code to draw graphics on different media.

Cairo's drawing model is similar to those provided by PostScript and PDF. The Cairo API provides such drawing operations as stroking and filling cubic Bézier splines, compositing images, and performing affine transformations. These vector operations allow for rich, anti-aliased graphics.

Cairo's rich drawing model allows for high-quality rendering to multiple media. The same API can be used to create on-screen graphics and text, to render images, or create crisp output suitable for printing.

You should use Cairo whenever you need to draw graphics in your application beyond the widgets provided by GTK+. Almost all of the drawing inside GTK+ is done using Cairo. Using Cairo for your custom drawing will allow your application to have high-quality, anti-aliased, and resolution-independent graphics.