Cousin Ricky <ric### [at] yahoocom> wrote:
> Tradeoffs, tradeoffs, tradeoffs.
>...
> I found the black borders on the smooth triangles unexpectedly
> disturbing.  They do show up on my height field hills under some
> circumstances, but are quite tolerable.  But seeing them cap my trees
> sent me straight to double_illuminate.  Disappointingly, double
> illumination had its own peculiarities near the shadow lines.  And when
> I added surface normals to the trees, it got really weird.

About your low-res smooth_triangle trees: I still think that at least the
edge-normal artifacts can be made to look a bit better.

I've been playing around with a low-res height_field, testing double_illuminate
vs. an inside_texture (a RED color in my example), and I think the latter can be
a more effective solution as a tradeoff. From the tests, it's clear that the
object's edge normals are not picking up any of the SKY color (YELLOW), but
rather, the black unlit 'inside' of the closed mesh. (The docs clearly explain
this 'reversed-normal' situation, of course.) But using the recommended
double_illuminate causes strange visual artifacts to appear on an 'applied'
normal{...}.

About the image:
There are to lights in the scene (one of very low intensity from the right, just
to help show some of the bumps normals on that side of the HF, rather than
completely featureless triangle faces that are in shadow.) That by itself helps
with the other problems a little bit.

Image 1 contains the edge artifacts, although they're difficult to see (your
trees are a better test case.)

Image 2-- using double_illuminate-- shows the changed appearance of the bumps
normal. (See the exact center of the image.)

Image 3 shows the true edge artifacts in all their glory ;-) But it also shows
that, by using an *appropriate* color for the inside_texture, it might be
possible to 'hide the edge artifacts in plain sight' so to speak. For example,
if the sky behind the tree edges is a light blue color, and the trees are olive
green, the inside_texture's pigment could be a 'mottled blend' between the two.
A quick and dirty example:
   pigment{
          bumps
          scale <...to be determined...>
          color_map{
                  [0 <...sky blue...>]
                  [1 <... tree green...>]
                   }
           --- some warp{turbulence...}---
           }
   finish{ambient 0 emission .5 diffuse 0}

The basic idea is to give a kind of random blue/green color to the edges of the
trees, in a broken-up way, to help them visually blend in better with the sky
and with their neighbors.

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