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

[Markus Mützel]

Follow-up Comment #6, bug #54922 (project octave):

Here the results with Matlab R2016a for a surface object:

>> format compact
>> clf;
>> Z = peaks ();
>> h = surf (Z, 'facelighting', 'none');
>> get (h, 'facelighting')
ans =
none
>> isempty(get (h, 'vertexnormals'))
ans =
     0
>> set (h, 'facelighting', 'gouraud')
>> isempty(get (h, 'vertexnormals'))
ans =
     0
>> hl = light ();
>> isempty(get (h, 'vertexnormals'))
ans =
     0


And for the sake of completeness with flat lighting:

>> clf;
>> Z = peaks ();
>> h = surf (Z, 'facelighting', 'none');
>> get (h, 'facelighting')
ans =
none
>> isempty(get (h, 'facenormals'))
ans =
     0
>> set(h, 'facelighting', 'flat')
>> isempty(get (h, 'facenormals'))
ans =
     0
>> hl = light ();
>> isempty(get (h, 'facenormals'))
ans =
     0


Similarly, for a patch object:

>> clf;
>> h = patch('facelighting', 'none');
>> get (h, 'facelighting')
ans =
none
>> isempty(get (h, 'vertexnormals'))
ans =
     1
>> set (h, 'facelighting', 'gouraud')
>> isempty(get (h, 'vertexnormals'))
ans =
     1
>> hl = light ();
>> drawnow
>> isempty(get (h, 'vertexnormals'))
ans =
     0


And with flat lighting:

>> clf;
>> h = patch('facelighting', 'none');
>> get (h, 'facelighting')
ans =
none
>> isempty(get (h, 'facenormals'))
ans =
     1
>> set(h, 'facelighting', 'flat')
>> isempty(get (h, 'facenormals'))
ans =
     1
>> hl = light ();
>> drawnow
>> isempty(get (h, 'facenormals'))
ans =
     0


So it looks like that delayed calculation of normals only applies to patch
objects. Both kinds of normals seem to be calculated for surfaces
immediately.

Calculating the normals for surfaces is easier because all vertices are on a
regular grid (no self-intersection, ...). The logic involved for patches is
more complex. That might be a motivation for the difference in behavior.
Is this what we want to do as well? If yes, I can try to create a patch over
the weekend.

This would also fix surfl without any further changes to the function itself.

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