GTK Scene Graph Kit (GSK) is the rendering and scene graph API for GTK introduced with version 3.90. GSK lies between the graphical control elements (widgets) and the rendering.

Like GDK, GSK is part of GTK and licensed under the GNU Lesser General Public License (LGPL).

GSK is part of GTK. GSK is meant to be used by GTK itself and by GTK-based applications that wish to replace Clutter for their UI. Applications that made use of Clutter instead of using only GTK are e.g. GNOME Shell, GNOME Videos, GNOME Boxes and Cheese.

Any application which makes use of GTK's graphical control elements (widgets), as opposed to those applications getting a GTK window and then drawing themselves on it, benefit from GSK.

Drawing graphical control elements (widgets) without a scenegraph leads to rendering things that don't show up on the screen, things that do not need to be rendered; hence it leads to avoidable performance and battery life losses. The scenegraph is used to do hidden surface determination.

The way widgets were drawn in GTK (when not using Clutter), was, that a draw function (part of GDK hence the name (GIMP "Drawing" Kit)) drew everything. There was no way to know, what has just been drawn. To know where the mouse pointer was currently hovering over, the current position had to be computed. With GSK, it should be fairly easy to write complex graphical control elements (widgets) and still track easily the whereabout of the mouse pointer.

It was decided for GTK to move to a Cascading Style Sheet (CSS)-based model for how graphical control elements (widgets) are styled (i.e. themed/skinned) and rendered. In CSS, shadows, borders, padding and style properties have well-defined semantics. Some of those semantics are difficult to implement with the old GTK drawing model.

GSK makes use of graphene, an external library which houses a collection of geometry types — points, sizes, rectangles, vectors, quads, quaternions, matrices. graphene has been ported to the Meson build system.