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annotate scripts/plot/appearance/specular.m @ 20787:40ed9b46a800

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new octave_value::string_value method with optional error message * ov.h (octave_value::string_vector): New method. ov-base.cc, ov-base.h (octave_base_value::string_vector): New default method. ov-str-mat.cc, ov-str-mat.h (octave_char_matrix_str::string_value): New method.
author John W. Eaton <jwe@octave.org>
date Thu, 08 Oct 2015 16:43:22 -0400
parents 83792dd9bcc1
children
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1 ## Copyright (C) 2009-2015 Kai Habel
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {} specular (@var{sx}, @var{sy}, @var{sz}, @var{lv}, @var{vv})
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21 ## @deftypefnx {Function File} {} specular (@var{sx}, @var{sy}, @var{sz}, @var{lv}, @var{vv}, @var{se})
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22 ## Calculate the specular reflection strength of a surface defined by the
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23 ## normal vector elements @var{sx}, @var{sy}, @var{sz} using Phong's
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24 ## approximation.
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25 ##
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26 ## The light source location and viewer location vectors are specified using
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27 ## parameters @var{lv} and @var{vv} respectively. The location vectors can
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28 ## given as 2-element vectors [azimuth, elevation] in degrees or as 3-element
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29 ## vectors [x, y, z].
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30 ##
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31 ## An optional sixth argument specifies the specular exponent (spread) @var{se}.
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32 ## If not given, @var{se} defaults to 10.
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33 ## @seealso{diffuse, surfl}
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34 ## @end deftypefn
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35
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36 ## Author: Kai Habel <kai.habel@gmx.de>
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37
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38 function retval = specular (sx, sy, sz, lv, vv, se)
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39
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40 if (nargin < 5 || nargin > 6)
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41 print_usage ();
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42 endif
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43
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44 ## Check normal vectors
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45 if (! size_equal (sx, sy, sz))
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46 error ("specular: SX, SY, and SZ must be the same size");
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47 endif
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48
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49 ## Check light vector (lv) argument
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50 if (! isvector (lv) || length (lv) < 2 || length (lv) > 3)
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51 error ("specular: light vector LV must be a 2- or 3-element vector");
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52 elseif (length (lv) == 2)
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53 [lv(1), lv(2), lv(3)] = sph2cart (lv(1) * pi/180, lv(2) * pi/180, 1.0);
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54 endif
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55
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56 ## Check view vector (vv) argument
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57 if (! isvector (vv) || length (vv) < 2 || length (lv) > 3)
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58 error ("specular: view vector VV must be a 2- or 3-element vector");
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59 elseif (length (vv) == 2)
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60 [vv(1), vv(2), vv(3)] = sph2cart (vv(1) * pi / 180, vv(2) * pi / 180, 1.0);
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61 endif
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62
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63 ## Check specular exponent (se) argument
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64 if (nargin < 6)
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65 se = 10;
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66 elseif (! (isnumeric (se) && numel (se) == 1 && se > 0))
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67 error ("specular: exponent SE must be a positive scalar");
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68 endif
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69
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70 ## Normalize view and light vectors
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71 if (sum (abs (lv)) > 0)
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72 lv /= norm (lv);
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73 endif
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74 if (sum (abs (vv)) > 0)
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75 vv /= norm (vv);
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76 endif
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77
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78 ## Calculate normal vector lengths and dot-products
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79 ns = sqrt (sx.^2 + sy.^2 + sz.^2);
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80 l_dot_n = (sx * lv(1) + sy * lv(2) + sz * lv(3)) ./ ns;
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81 v_dot_n = (sx * vv(1) + sy * vv(2) + sz * vv(3)) ./ ns;
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82
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83 ## Calculate specular reflection using Phong's approximation
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84 retval = 2 * l_dot_n .* v_dot_n - dot (lv, vv);
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85
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86 ## Set reflectance to zero if light is on the other side
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87 retval(l_dot_n < 0) = 0;
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88
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89 ## Allow postive values only
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90 retval(retval < 0) = 0;
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91 retval .^= se;
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92
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93 endfunction
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94