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function img = beam_trace(beams, faces, borders, border_limits, img)
%% trace beam and all it reflections and refractions on faces
% for beams and faces structure description see face_beam_interaction.m
% border similar to faces cell array which enclose the beam
% i.e. it does not leave the polygon consisting of border faces
intensity_threshold = 1e-8; % intensity of the weakest beam which we still trace
Nbeams=size(beams)(2);
if ( Nbeams == 0 )
% no more beam to trace
return;
end
% trace each beam in beams cell array
for i=1:Nbeams
beam=beams{i};
[is_face_hit, hit_position, hit_distance, new_beams] = face_beam_interaction(beam, faces);
if (is_face_hit)
%% remove beams which are to weak to trace
N_new_beams=size(new_beams)(2);
intense_enough_beams={};
intense_beams_counter=0;
for k=1:N_new_beams
if ( new_beams{k}.intensity >= intensity_threshold )
intense_beams_counter=intense_beams_counter + 1;
intense_enough_beams{intense_beams_counter}=new_beams{k};
end
end
img = beam_trace(intense_enough_beams, faces, borders, border_limits, img);
else
% beam does not hit face but it should stop and borders
beam.face=NA;
[is_face_hit, hit_position, hit_distance, new_beams] = face_beam_interaction(beam, borders);
if (!is_face_hit)
error('borders are badly defined, the beam misses them');
end
end
img=make_beam_trace(beam, hit_position, border_limits, img);
end
end
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