OpenGL supports both RGBA and color index rendering. The RGBA mode is
generally preferable to color index because more OpenGL rendering
capabilities are available and color index mode requires the loading of
colormap entries.
The GLUT color index state variables are used to read and write entries in a
window's color index colormap. Every GLUT color index window has its own
logical color index colormap. The size of a window's colormap can be
determined by reading numColorMapEntries.
GLUT color index windows within a program can attempt to share colormap
resources by copying a single color index colormap to multiple windows using
copyColormap. If possible GLUT will attempt to share the actual colormap.
While copying colormaps using copyColormap can potentially allow sharing of
physical colormap resources, logically each window has its own colormap. So
changing a copied colormap of a window will force the duplication of the
colormap. For this reason, color index programs should generally load a
single color index colormap, copy it to all color index windows within the
program, and then not modify any colormap cells.
Use of multiple colormaps is likely to result in colormap installation
problems where some windows are displayed with an incorrect colormap due to
limitations on colormap resources.
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