Orchid Win7 v1 <voi### [at] devnull> wrote:
> On 08/07/2015 06:14 PM, Samuel Benge wrote:
> > scott<sco### [at] scottcom>  wrote:
> >>> The attached shows artifacts present at various accuracies for the function
> >>> sqrt(x*x+y*y+z*z)-1.>
> >>
> >> Assuming you've got no pattern displacement in any of those images, it
> >> looks to me like it's something to do with the shadow ray being started
> >> too close to the surface (and hence the tracer immediately thinks the
> >> shadow ray has been blocked by the isosurface itself).
> >
> > I should have guessed that, since I ran into shadow ray problems last summer
> > with the raymarching stuff. The shadow ray's origin had to be spaced from the
> > initial hit point (by backing it up toward the camera or outward from the
> > surface), or else artifacts would appear.
>
> Question: Does the problem go away if you make the spheres bigger? Like,
> say, 10 units across instead of just 1?

I just ran some tests. Scaled the isosurface and zoomed the camera; adjusted the
function radius and scaled the object; multiplied/divided the function to change
the gradient's falloff rate... all at values between .01 and 100. No change. You
end up just needing to adjust the accuracy and max_gradient, but the end result
is always the same.

> As I recall, POV-Ray tends to dislike rendering either very tiny or very
> large objects. Floating-point precision issues and all.

I was hoping that with 64 bit would come a more precise epsilon value, but it
didn't turn out that way :( Was it a misunderstanding on my part, or to keep
POV-Ray rendering the same on different architectures, I wonder?

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