Transparent Holes (Bubbles)
There's another useful trick for creating holes or bubbles inside a transparent object.
The trick doesn't give quite the same effect as using difference but the
result looks fairly realistic.
The trick is to use a union of bubbles that have their index of refraction
set to 1.0, but have all of their other texture parameters the same as the container.
Or, perhaps better, the material of the air bubble has the same texture
as the glass, but has no interior settings at all.
The object on the left in this image is the union of a cube with an ior 1.0 sphere,
and the image on the right is the difference of a cube with a sphere.
You can see subtle differences, but if I had not told you which one used the trick,
would you have known which one was physically correct?
These two images each contain 512 bubbles. One of the images uses the ior 1.0 trick
and rendered in 1 min 13 sec; the other uses a real difference and took
1 hour 3 min 2 sec to render.
In this image I've also made the air bubbles have
no_shadow because the bubbles were casting unrealistic white anti-shadows.
Other Tricks
Holes Tutorial Part 1
Holes Tutorial Part 2: Iso-Holes
Holes Tutorial Part 4: Blob-Holes
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