// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
// Copyright (C) INRIA
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution.  The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt

function [xx,yy,zz]=genfac3d(x,y,zmat,mask)

    // genfac - transforms  standard 3d data to four sides facets representation
    //%Syntax
    // [xx,yy,zz]=genfac3d(x,y,zmat,mask)
    //%Parameters
    // zmat      : matrix , zmat(i,j)= F(x(j),y(i))
    // x        : x axis coordinates vector
    // y        : y axis coordinates vector
    // mask     : boolean optional matrix with same size as zmat used to select
    //            entries of zmat to be represented by facets
    // xx,yy,zz :4xn  matrices. xx(:,i),yy(:,i),zz(:,i) are respectively the
    //           x-axis,y-axis and z-axis coordinates of the ith facet
    //%Examples
    //  genfac3d()
    //!

    [lhs,rhs]=argn(0)

    if rhs <= 0 then   // demo
        t=(0:10)'*%pi/5;
        zmat=sin(t)*cos(t');
        [xx,yy,zz]=genfac3d(t,t,zmat,zmat>=0);
        plot3d(xx,yy,zz);
        return
    end

    if rhs<3 then
        error(msprintf(gettext("%s: Wrong number of input argument(s): At least %d expected.\n"), "genfac3d", 3));
    end

    [nr,nc]=size(zmat)
    indy=(ones(1,nc-1).*.[0;1;1;0]+(1:nc-1).*.[1;1;1;1]).*.ones(1,nr-1);
    indx=ones(1,nc-1).*.(ones(1,nr-1).*.[0;0;1;1]+(1:nr-1).*.[1;1;1;1]);
    [nrl,nrc]=size(indx)
    indx=matrix(indx,nrl*nrc,1);
    indy=matrix(indy,nrl*nrc,1);
    indz=indx+(nr)*(indy-1*ones(indy));
    [nrl,nrc]=size(indx);
    xx=matrix(x(indx),4,nrl*nrc/4);
    yy=matrix(y(indy),4,nrl*nrc/4);
    zz=matrix(zmat(indz),4,nrl*nrc/4);
    if rhs==4 then
        zl=matrix(mask(indz),4,nrl*nrc/4);
        [xin,yin]=find(zl);
        zz=zz(:,yin);
        xx=xx(:,yin);
        yy=yy(:,yin);
    end
endfunction