Iris GL & OpenGL

[Bill Brown]

Andreas,

We have looked at some free graphics libraries and have chosen
OpenGL instead for several reasons.  1) some of the more advanced features 
such as alpha blending for transparency and texture mapping are missing
from some of the free libraries.  2) the free libraries tend to require
much more memory overhead for the volume of polygons needed for many
GIS applications.  3) OpenGL, as a detailed specification for an API,
allows hardware vendors to build in support for hardware acceleration
of graphics.  4)  If we develop applications using a non-standard
library with little documentation, people who want to take advantage
of hardware acceleration of OpenGL or port it to their favorite GL would
have a harder time than if we write it using a well documented & specified
standard such as OpenGL.  5) We already have a lot of code in which 
we used GL, and porting it to OpenGL is just plain easier & more
cost effective.

While some of the limitations of OpenGL (such as no Phong shading and
awkward switching from single to double buffer modes) are frustrating,
we have chosen to live with its limitations and exploit its strengths.

On the brighter side, we are being much more careful in current 
development to contain graphics calls. Rather than have many functions
calling graphics routines, as we did in SG3d (which was never really
expected to run using anything but GL), we have done a much better
job of grouping graphic primitives to perform specific tasks such as
surface rendering and have built a library which is completely 
separate from the interface.  So it may turn out that porting to
a free library (perhaps with some loss of functionality) will not
be exceeding difficult for somebody else to do.  If a FreeGL version
of OpenGL is ever produced, it could be a rather trivial port.

Thanks for you input,

- Bill