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[Octave-bug-tracker] [bug #54922] demo surfl 1 fails

From: Rik
Subject: [Octave-bug-tracker] [bug #54922] demo surfl 1 fails
Date: Wed, 31 Oct 2018 17:21:29 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:63.0) Gecko/20100101 Firefox/63.0

Update of bug #54922 (project octave):

                  Status:         Patch Submitted => Patch Reviewed         


Follow-up Comment #3:

I agree that we don't want to calculate the normals unless it is necessary.

is a little unclear about when it calculates the normals.  "If you do not
specify normal vectors, then the surface generates this data for lighting
calculations."  Does that mean only when a light object is added?  Only when
the "facelighting" property changes?

If you have access to Matlab the following code would be useful to test.

Z = peaks ();
h = surf (Z, 'facelighting', 'none');
get (h, 'facelighting')
get (h, 'vertexnormals')
set (h, 'facelighting', 'gouraud')
get (h, 'vertexnormals')
hl = light ();
get (h, 'vertexnormals')

In the NEWS section, the description begins

 ** "FaceNormals" and "EdgeNormals" for patch and surface graphic

But, I don't see any graphic property called "EdgeNormals" for patches or
surfaces.  Should this be "VertexNormals"?

I think it would be a good idea to add to the description in NEWS the
conditions required before the "*Normals" will be calculated.  Something, like
'The "FaceLighting" property must be set to "flat" (FaceNormals) or "gouraud"
(VertexNormals), AND a light object must be present in the axes, before any
normals will be calculated.

I would add a FIXME note in surfl.m above where you create a light object and
then immediately delete it.  Without any explanation, it looks weird, and
someone at a later date might come along and try to clean up the code by
removing it.

Finally, and this might be the subject of a separate bug report, the
documentation for surfl says

The default lighting mode "cdata", changes the cdata property of
the surface object to give the impression of a lighted surface.
*Warning:* The alternative mode "light" mode which creates a light
object to illuminate the surface is not implemented (yet).

Since light objects now exist, couldn't this option be implemented?


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