Daniel Adler and Oleg Nenadic
A Framework for an R to OpenGL Interface for Interactive 3D graphics
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We describe a framework for providing interactive 3D graphics in R. The key
component is the interface between R and OpenGL, which provides a set of
commands for specifying objects and operations that enable three-dimensional
graphical visualization. An alpha version of the software, the core of which
is written in ANSI-compliant C++, is available for testing and feedback (Win32
and X11).

An important goal in the design has been to facilitate portability to different
operating systems. An object-oriented approach is used throughout. A simple and
intuitive user interface for navigating in 3D using a pointer device is provided
by moving the viewer around the surface of a sphere that surrounds the relevant
space; the view is focussed on the centre of the sphere.

The focus of the current implementation is to manipulate 3D ``primitives" (for
example points, lines, triangles, quads, spheres, text, etc.) which constitute the
building blocks for more complex 3D objects (such as histograms, perspective plots,
scatterplot, axes, etc. ). A number of attractive OpenGL features, such as multiple
lighting, fog, texture-mapping, alpha-blending (transparency) and side-dependent
rendering are accessible directly from R via functions that control shapes and
appearance. Further functions control device-and-scene management (opening closing
windows, clearing selected objects),  environment setup (setting lights, bounding
boxes, viewpoints) and export (making and exporting snapshots). The calling sequences
are similar to those used in the existing and familiar R graphics functions, such as
persp.