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annotate scripts/plot/specular.m @ 10793:be55736a0783

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Grammarcheck the documentation from m-files.
author Rik <octave@nomad.inbox5.com>
date Sun, 18 Jul 2010 20:35:16 -0700
parents d1978e7364ad
children c776f063fefe
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1 ## Copyright (C) 2009 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{l}, @var{v})
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21 ## @deftypefnx {Function File} {} specular (@var{sx}, @var{sy}, @var{sz}, @var{l}, @var{v}, @var{se})
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22 ## Calculate specular reflection strength of a surface defined by the normal
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23 ## vector elements @var{sx}, @var{sy}, @var{sz} using Phong's approximation.
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24 ## The light and view vectors can be specified using parameter @var{L} and
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25 ## @var{V} respectively.
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26 ## Both can be given as 2-element vectors [azimuth, elevation] in degrees or as
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27 ## 3-element
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28 ## vector [x, y, z]. An optional 6th argument describes the specular exponent
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29 ## (spread) @var{se}.
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30 ## @seealso{surfl, diffuse}
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31 ## @end deftypefn
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32
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33 ## Author: Kai Habel <kai.habel@gmx.de>
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34
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35 function retval = specular (sx, sy, sz, lv, vv, se)
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36
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37 if (nargin < 5 || nargin > 6)
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38 print_usage ();
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39 endif
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40
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41 ## Checks for specular exponent (se).
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42 if (nargin < 6)
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43 se = 10;
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44 else
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45 if (!isnumeric (se) || numel (se) != 1 || se <= 0)
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46 error ("specular: exponent must be positive scalar");
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47 endif
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48 endif
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49
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50 ## Checks for normal vector.
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51 if (!size_equal (sx, sy, sz))
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52 error ("specular: SX, SY, and SZ must have same size");
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53 endif
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54
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55 ## Check for light vector (lv) argument.
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56 if (length (lv) < 2 || length (lv) > 3)
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57 error ("specular: light vector LV must be a 2- or 3-element vector");
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58 elseif (length (lv) == 2)
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59 [lv(1), lv(2), lv(3)] = sph2cart (lv(1) * pi/180, lv(2) * pi/180, 1.0);
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60 endif
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61
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62 ## Check for view vector (vv) argument.
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63 if (length (vv) < 2 || length (lv) > 3)
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64 error ("specular: view vector VV must be a 2- or 3-element vector");
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65 elseif (length (vv) == 2)
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66 [vv(1), vv(2), vv(3)] = sph2cart (vv(1) * pi / 180, vv(2) * pi / 180, 1.0);
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67 endif
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68
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69 ## Normalize view and light vector.
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70 if (sum (abs (lv)) > 0)
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71 lv /= norm (lv);
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72 endif
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73 if (sum (abs (vv)) > 0)
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74 vv /= norm (vv);
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75 endif
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76
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77 ## Calculate normal vector lengths and dot-products.
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78 ns = sqrt (sx.^2 + sy.^2 + sz.^2);
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79 l_dot_n = (sx * lv(1) + sy * lv(2) + sz * lv(3)) ./ ns;
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80 v_dot_n = (sx * vv(1) + sy * vv(2) + sz * vv(3)) ./ ns;
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81
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82 ## Calculate specular reflection using Phong's approximation.
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83 retval = 2 * l_dot_n .* v_dot_n - dot (lv, vv);
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84
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85 ## Set zero if light is on the other side.
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86 retval(l_dot_n < 0) = 0;
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87
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88 ## Allow postive values only.
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89 retval(retval < 0) = 0;
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90 retval = retval .^ se;
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91
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92 endfunction