clipRay

 Clip a ray with a box.

   EDGE = clipRay(RAY, BOX);
   RAY is a straight ray given as a 4 element row vector: [x0 y0 dx dy],
   with (x0 y0) being the origin of the ray and (dx dy) its direction
   vector, BOX is the clipping box, given by its extreme coordinates: 
   [xmin xmax ymin ymax].
   The result is given as an edge, defined by the coordinates of its 2
   extreme points: [x1 y1 x2 y2].
   If the ray does not intersect the box, [NaN NaN NaN NaN] is returned.
   
   Function works also if RAY is a N-by-4 array, if BOX is a Nx4 array, or
   if both RAY and BOX are N-by-4 arrays. In these cases, EDGE is a N-by-4
   array.
      
   See also:
     rays2d, boxes2d, edges2d, clipLine, drawRay

0001 function [edge, isInside] = clipRay(ray, bb)
0002 % Clip a ray with a box.
0003 %
0004 %   EDGE = clipRay(RAY, BOX);
0005 %   RAY is a straight ray given as a 4 element row vector: [x0 y0 dx dy],
0006 %   with (x0 y0) being the origin of the ray and (dx dy) its direction
0007 %   vector, BOX is the clipping box, given by its extreme coordinates:
0008 %   [xmin xmax ymin ymax].
0009 %   The result is given as an edge, defined by the coordinates of its 2
0010 %   extreme points: [x1 y1 x2 y2].
0011 %   If the ray does not intersect the box, [NaN NaN NaN NaN] is returned.
0012 %
0013 %   Function works also if RAY is a N-by-4 array, if BOX is a Nx4 array, or
0014 %   if both RAY and BOX are N-by-4 arrays. In these cases, EDGE is a N-by-4
0015 %   array.
0016 %
0017 %   See also:
0018 %     rays2d, boxes2d, edges2d, clipLine, drawRay
0019 %
0020 
0021 % ------
0022 % Author: David Legland
0023 % e-mail: david.legland@inrae.fr
0024 % Created: 2010-05-13,    using Matlab 7.4.0.287 (R2007a)
0025 % Copyright 2010 INRA - Cepia Software Platform.
0026 
0027 %   HISTORY
0028 %   2010-05-13 create from clipLine
0029 %   2017-09-21 simplify code
0030 
0031 % adjust size of two input arguments
0032 if size(ray, 1) == 1
0033     ray = repmat(ray, size(bb, 1), 1);
0034 elseif size(bb, 1) == 1
0035     bb = repmat(bb, size(ray, 1), 1);
0036 elseif size(ray, 1) ~= size(bb, 1)
0037     error('bad sizes for input');
0038 end
0039 
0040 % first compute clipping of supporting line
0041 edge = clipLine(ray, bb);
0042 
0043 % detects valid edges (edges outside box are all NaN)
0044 inds = find(isfinite(edge(:, 1)));
0045 
0046 % compute position of edge extremities relative to the ray
0047 pos1 = linePosition(edge(inds,1:2), ray(inds,:), 'diag');
0048 pos2 = linePosition(edge(inds,3:4), ray(inds,:), 'diag');
0049 
0050 % if first point is before ray origin, replace by origin
0051 edge(inds(pos1 < 0), 1:2) = ray(inds(pos1 < 0), 1:2);
0052 
0053 % if last point of edge is before origin, set all edge to NaN
0054 edge(inds(pos2 < 0), :) = NaN;
0055 
0056 % eventually returns result about inside or outside
0057 if nargout > 1
0058     isInside = isfinite(edge(:,1));
0059 end