[Scilab-users] Regression: Fac3d direct surfaces along cartesian axis, no matter user definition

[Pierre Payen]

Answering  this stackoverflow question
<https://stackoverflow.com/questions/46050997/how-do-i-determine-orientation-of-vertices-in-scilab-3dplot> 
, when using plot3d to plot a custom surface, if this surface is directed
along x (respectively y  or z)  meaning that any vector collinear to x
(respect to y or z) is normal to the surface, then the outside color will
always be in the direction of the axis. 

Bugzilla beeing down, i could not see if this bugs was already know.

below a small testscript to replicate the problem.

/////////////////////////////////////////////////////////////////////////////////////////////////////////
clc
clear
xdel(winsid())

figure(1)
set(gcf(),'background',-2)
cr=color('red') // color of the outside surface

P1 = [0,0,0] //
P2 = [0,1,0]
P3 = [1,0,0]

F1 = [P1;P2;P3] // defining surface clockwise
F2 = [P1;P3;P2] //                  counterclockwise

subplot(2,2,1)
plot3d(F1(:,1),F1(:,2),list(F1(:,3),cr*ones(F1(:,3))))
xstring(F1(:,1),F1(:,2),['P1','P2','P3']) 
title('surface is [P1,P2,P3] with z_P3=0')
set(gca(),'data_bounds',[0,1,0,1,-1,1])

subplot(2,2,2)
plot3d(F2(:,1),F2(:,2),list(F2(:,3),cr*ones(F2(:,3))))
xstring(F2(:,1),F2(:,2),['P1','P3','P2'])
title('surface is [P1,P3,P2] with z_P3=0, broken with Scilab 6.0.0')
set(gca(),'data_bounds',[0,1,0,1,-1,1])

subplot(2,2,3)
plot3d(F2(:,1),F2(:,2),list(F2(:,3)+[0;0;10^-7],cr*ones(F2(:,3))))
xstring(F2(:,1),F2(:,2),['P1','P3','P2'])
title('surface is [P1,P3,P2] with |z_P3| < 10^-8')
set(gca(),'data_bounds',[0,1,0,1,-1,1])

subplot(2,2,4)
plot3d(F2(:,1),F2(:,2),list(F2(:,3)+[0;0;10^-8],cr*ones(F2(:,3))))
xstring(F2(:,1),F2(:,2),['P1','P3','P2'])
title('surface is [P1,P3,P2] with |z_P3| = 10^-8, broken in 6.0.0')
set(gca(),'data_bounds',[0,1,0,1,-1,1])
//////////////////////////////////////////////////////////////////////////////////////////////////////////////
and the outputs 

Scilab 5.5.1
<http://mailinglists.scilab.org/file/t497474/7Dgik.png> 
Scilab 6.0.0
<http://mailinglists.scilab.org/file/t497474/aIZXv.png> 




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