IBL: ability to create different sized maps for Skybox and radiance

[dar-dev]

For quality reason and GPU usage sometimes it would be better to create high resolution skybox and low res radiance maps.

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[mgsx-dev]

That's already the case :-) see

gdx-gltf/ibl-composer/src/net/mgsx/gltf/ibl/model/IBLSettings.java

Line 7 in 08779fc

public int envMapSize;