fsleyes.gl. More to come.

routines. Change meaning of GL_VERSION field, and add GL_COMPATIBILITY
field. Add new glIsSoftwareRenderer function to test for software GL renderer.

may add back in after checking)

when lighting is on, and I don't think will have any other adverse effect.

that they (and the light effect) were being affected by zoom level

toggle (can't be bothered implementing)

it useful to disable sometimes).

for lighting

planes are active

specifies the distance from centre. Changes to pos/distance will trigger
a canvas refresh - do this rather than GLObjects needing to listen for
changes.