Use of GLSL for vertex and fragment programs in Qt
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We don't compile the *.glsl files because we don't want the build process of
Qt to require cgc from nVidia to build the fragment programs.

The script src/opengl/util/glsl_to_include.sh will compile a GLSL program to a file
that can be included in a C(++) program. The file is the output from cgc
quoted as a string.

This can be done manually by:

./glsl_to_include.sh radial.glsl
./glsl_to_include.sh conical.glsl

This will produce the files radial.frag and radial.glsl_quoted.
(and also conical.frag and conical.glsl_quoted)
These files are included by qpaintengine_opengl.cpp
