[Octave-bug-tracker] [bug #65421] patch fails to render if cdata is specified before geometry in property/value calling form

[Markus Mützel]

Follow-up Comment #36, bug #65421 (group octave):

A reproducer with only `set` function calls:

vertices = [2.5, 7.5; 6.5, 7.0; 2.5, 5.5; 6.5, 6.0; 1.0, 6.5; 8.0, 6.5];

faces = [5, 3, 1; 1, 4, 2; 1, 3, 4; 4, 6, 2];

vert_color = (1:6).';  # index to colormap

cdata = vert_color(faces).';

hf = figure ();
clf (hf);
hax = axes (hf);
hp = patch (hax);

## step 1
set (hp, 'vertices', vertices);
v1 = get (hp, 'vertices')
f1 = get (hp, 'faces')
fvc1 = get (hp, 'facevertexcdata')
cd1 = get (hp, 'cdata')

## step 2
# set (hp, 'facevertexcdata', vert_color);
set (hp, 'cdata', cdata);
v2 = get (hp, 'vertices')
f2 = get (hp, 'faces')
fvc2 = get (hp, 'facevertexcdata')
cd2 = get (hp, 'cdata')


## step 3
set (hp, 'faces', faces);
v3 = get (hp, 'vertices')
f3 = get (hp, 'faces')
fvc3 = get (hp, 'facevertexcdata')
cd3 = get (hp, 'cdata')


When setting 'cdata' (which in general might require duplicating vertices)
before setting 'faces', the color data is lost.
If you invert steps 2 and 3 or set 'facevertexcdata' instead of 'cdata', the
color data isn't lost.

To be honest, it is quite unusual that a patch would be created with
'vertices' and 'faces' but the color data would be provided by 'cdata'.
More commonly, the color data comes from the "same sources" where the geometry
comes from. So, it would be more usual to set a combination of either
'vertices', 'faces', and 'facevertexcdata', or 'xdata', 'ydata', ('zdata',)
and 'cdata'.

The entire use-case looks pretty much constructed. So, fixing this has
probably a low priority.


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