sync with brain2mesh, polylinelen output oriented curve

polylinelen.m

@@ -1,6 +1,6 @@
-function [len, node]=polylinelen(node, p0, p1, pmid)
+function [len, node, inputreversed]=polylinelen(node, p0, p1, pmid)
 %
-% [len, node]=polylinelen(node, p0, p1)
+% [len, node, inputreversed]=polylinelen(node, p0, p1, pmid)
 %
 % Calculate the polyline line segment length vector in sequential order
 %
@@ -19,6 +19,7 @@
 % output:
 %    len: the length of each segment between the start and the end points
 %    node: the node list between the start and end points of the polyline
+%    inputreversed: if 1, the input node is reversed from p0 to pmid to p1
 %
 %
 % -- this function is part of brain2mesh toolbox (http://mcx.space/brain2mesh)
@@ -47,13 +48,23 @@
 end
 
 if(p0<pmid && pmid<p1)
+    inputreversed=0;
     node=node(p0:p1,:);
 elseif(p0<pmid && p1<pmid)
+    inputreversed=(min(p0,p1) == p0);
     node=node([min(p0,p1):-1:1 end:-1:max(p0,p1)],:);
+    if(~inputreversed)
+        node=flipud(node);
+    end
 elseif(p0>pmid && pmid>p1)
+    inputreversed=1;
     node=node(p0:-1:p1,:);
 elseif(p0>pmid && p1>pmid)
+    inputreversed=(max(p0,p1) == p1);
     node=node([max(p0,p1):end 1:min(p0,p1)],:);
+    if(inputreversed)
+        node=flipud(node);
+    end
 end
 
 len=node(1:end-1,:) - node(2:end,:);

ray2surf.m

@@ -0,0 +1,75 @@
+function [p,e0]=ray2surf(node,elem,p0,v0,e0)
+%
+% [p,e0]=ray2surf(node,elem,p0,v0,e0)
+%
+% Determine the entry position and element for a ray to intersect a mesh
+%
+% author: Qianqian Fang (q.fang <at> neu.edu)
+%
+% input:
+%     node: the mesh coordinate list
+%     elem: the tetrahedral mesh element list, 4 columns
+%     p0: origin of the ray
+%     v0: direction vector of the ray
+%     e0: search direction: '>' forward search, '<' backward search, '-' bidirectional
+%
+% output:
+%     p: the intersection position
+%     e0: if found, the index of the intersecting element ID
+%
+% this file is part of Mesh-based Monte Carlo (MMC)
+%
+% License: GPLv3, see http://mcx.sf.net/mmc/ for details
+%
+
+p=p0;
+if(size(elem,2)==3)
+    face=elem;
+else
+    face=volface(elem);
+end
+[t,u,v,idx]=raytrace(p0,v0,node,face);
+if(isempty(idx))
+    error('ray does not intersect with the mesh');
+else
+    t=t(idx);
+    if(e0=='>')
+%         idx1=find(t>=0);
+        idx1=find(t>=1e-10);
+    elseif(e0=='<')
+        idx1=find(t<=0);
+    elseif(isnan(e0) || e0=='-')
+        idx1=1:length(t);
+    else
+        error('ray direction specifier is not recognized');
+    end
+    if(isempty(idx1))
+        error('no intersection is found along the ray direction');
+    end
+    t0=abs(t(idx1));
+    [tmin,loc]=min(t0);
+    faceidx=idx(idx1(loc));
+
+    % update source position
+    p=p0+t(idx1(loc))*v0;
+
+    if(nargout<2)
+        return;
+    end
+
+    % find initial element id
+    if(size(elem,2)==3)
+        e0=faceidx;
+    else
+       felem=sort(face(faceidx,:));
+       f=elem;
+       f=[f(:,[1,2,3]);
+          f(:,[2,1,4]);
+          f(:,[1,3,4]);
+          f(:,[2,4,3])];
+       [tf,loc]=ismember(felem,sort(f,2),'rows');
+       loc=mod(loc,size(elem,1));
+       if(loc==0) loc=size(elem,1); end
+       e0=loc;
+    end
+end