POV-Ray : Newsgroups : povray.general : Smooth level for smooth_triangle. : Re: Smooth level for smooth_triangle. Server Time
1 Mar 2024 18:38:33 EST (-0500)
  Re: Smooth level for smooth_triangle.  
From: Bald Eagle
Date: 21 Nov 2023 18:25:00
Message: <web.655d3c1484c692a31f9dae3025979125@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:

> I am looking forward to seeing how you solve your too-smooth problem; I wish
> that I could offer some suggestions. Some of this triangle stuff is outside my
> knowledge.  *If* the triangle normals are all unit length, perhaps your summing
> operation could be made to eliminate some of the identical normals on large flat
> areas, which might reduce their contribution-- and make the smoothness less
> smooth. (?)

Triangles typically have a sinlge normal - a vector that is perpendicular to
it's face (in either direction).

The normal can be of any length.

Typically, for lighting purposes, since the normal vector is used to calculate
how light interacts with the surface, you want them of unit length.

For smooth, or perturbed-surfaces, you will specify the normals of the vertices,
and then POV-Ray will interpolate the normals across the surface, (and perhaps
adding/multiplying by some pattern) to yield a smoothly changing surface.

When dealing with a mesh of triangles that share common vertices and edges, one
typically averages all of the normals that meet at a common vertex so that
there's no sudden discontinuity in the way light reflects from the surface,
appearing as lump, depressions, or creases.

If you have two triangles oriented in different directions, if you multiply the
length of the normal of one triangle, its contribution to how the triangles
behave at that vertex will be greater.

I think in order to accomplish what he's looking to do, the way that the
triangles get interpolated would have to change, other wise I don't see how to
maintain a common normal direction on one end, and non-linearly change apparent
curvature at the other.

It's not something I've played with in detail, but it sure seems like something
that ought to be explored with test renders, diagrams, normal directions and
lengths explicitly labeled, etc.

Good instructional articles are what draw computer graphics students and
hobbyists to any given site for the quality content.

We should have that.
Right on the home page.  Perhaps directing to a specific (new) sub-group titled
"Articles".

- BW


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