Re: possible bug in gnuplot backend when using 3d patches

[Martin Helm]

Am 31.03.2012 17:03, schrieb Ben Abbott:
> On Mar 30, 2012, at 7:59 PM, Martin Helm wrote:
>
>> Dear all,
>>
>> I would like to have some feedback on the following problem (octave 3.6.1)
>>
>> This code works as expected when using the fltk toolkit
>>
>> patch ("Faces", [1 2 3; 2 3 4; 3 4 1; 4 1 2], \
>> "Vertices", [1 0 0; 0 1 0; 1 1 0; 0 0 1],\
>> "FaceVertexCData", [32; 32; 32; 32])
>>
>> and shows as expected a tetrahedron with color 32 of the current colormap.
>>
>> The same code when used with the gnuplot backend leads to this error
>>
>> error: horizontal dimensions mismatch (4x3 vs 2x1)
>> error: called from:
>> error:   /usr/share/octave/3.6.1/m/plot/private/__go_draw_axes__.m at
>> line 752, column 37
>> error:   /usr/share/octave/3.6.1/m/plot/private/__go_draw_figure__.m at
>> line 167, column 19
>> error:   /usr/share/octave/3.6.1/m/plot/__gnuplot_drawnow__.m at line
>> 86, column 5
>>
>> while it works somehow when I feed rgb tripplets to the patch
>> colormap()(32,:)
>> ans =
>>
>>   0.46825   1.00000   0.53175
>>
>> patch ("Faces", [1 2 3; 2 3 4; 3 4 1; 4 1 2], \
>> "Vertices", [1 0 0; 0 1 0; 1 1 0; 0 0 1], \
>> "FaceVertexCData", [ 0.46825   1.00000   0.53175;\
>>  0.46825   1.00000   0.53175;\
>>  0.46825   1.00000   0.53175;\
>>  0.46825   1.00000   0.53175])
>>
>> But also not as I would expect, there is some spurious red-brown
>> triangle there which I cannot explain.
>>
>> Has anyone an idea if that's a bug or some feature I do not understand?
> The problem is that the patches are 3D, and gnuplot has limited ability to 
> render 3D patches.
>
> h = findobj (gca (), "type", "patch");
> get (h, "zdata")
> ans =
>
>    0   0   0   1
>    0   0   1   0
>    0   1   0   0
>
> Take a look at how David Bateman implemented isosurface.m
>
>       demo isosurface 1
>       h = get (gca (), "children")
>       get (h, "type")
>       ans = patch
>
> There remains some minor problems with isosurface. The edge color is [0 0 0], 
> but should be "none".  However, when the edgecolor is an RGB value, gnuplot 
> does not render the edge.
>
> Ben
>
>
>
>
Hi Ben, I know the problem with isosurface and gnuplot (since I
implemented it, it is just not checked in by me). I will have a look
into the source code for the 3d patches in gnuplot (but feel a bit
lost), I remember I could work around that problems a few years ago by
directly creating pm3d gnuplot code and passing it to gnuplot directly
which did not have all of that problems, though I do not remeber if I
ever found a solution for the edge color problem.
Maybe I find a solution, if I can find out what I did at that time.