Yair Kurzion (yair++at++polygon.engr.sgi.com)
Wed, 3 Feb 1999 12:18:31 -0800 (PST)
> most of the utilities concerning ASD don't generate
> normals, is there a reason why? Even with textures, the terrain lacks
> detail if each vertex has the same normal. Is this something that will
> be incorporated into future versions of the ASD utils?
First, paging-ASD's do not page texture, color, or normals. So, even if you
can create these attributes, ASD will not page them. This isn't an inherent
problem. We just didn't implement it.
As for non-paging ASD's: one of the best things about ASD's is that you don't
see any popping. ASD models with vertex normals often cause popping:
In the drawing below, take the case where we replace a low LOD triangle
(v0, v1, v2) with four co-planar higher-LOD triangles. Look at a triangle edge
(v0, v1) that gets split by a split point sp. The point sp on the parent
triangle gets a Gouraud shaded color based on the edge endpoints v0 and v1.
The new split point has a normal so its color is computed using the normal
directly. This color is usually different from the Gouraud shaded one so you
get a popping effect.
v0
/\
/ \
/ \
/______\ sp
/\ /\
/ \ / \
/ \ / \
v2/______\/______\ v1
In terrain applications, you often don't care for specular reflections off the
terrain. So, in order to add the missing detail and avoid the popping effect,
you can paint the vertices with the diffuse/ambient components of the colors.
This painting is of course correct for a fixed hour of the day, and changing
the time requires re-painting. However, since the sun position changes rather
slowly, you can run an asynchronous process (DBASE) for re-painting the
terrain. But I am already designing your system for you so I better stop here.
-yair
--
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