For some recent modeling work, I have had a need to create various objects based
on cylinder-based shapes, varying the radius of the cylinder based on the
y-axis.

Examples:
sqrt(x*x+z*z) - Radius // cylinder
sqrt(x*x+z*z) - Radius*y/Height // inverted cone

These seem to render as isosurfaces pretty consistently without high
max_gradients or the need for high accuracy.

However:
sqrt(x*x+z*z) - Radius*(pow(y/Height,2)) // quadratic
or
sqrt(x*x+z*z) - Radius*sqrt(y/Height)

is causing the object to look semi-transparent, allowing light to pass through
it in an almost even distribution.

In a fit of frustration, after trying very high accuracy and max_gradient
values, I tried

sqrt(x*x+z*z) - Radius*sin(0.5*pi*y/Height)

and the object looks completely solid.

So, I'm wondering what in the isosurface code could cause this difference?

-- Chris R.

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