1 | /* -*- mode: C; tab-width:8; c-basic-offset:8 -*- |
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2 | * vi:set ts=8: |
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3 | * |
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4 | * al_distance.c |
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5 | * |
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6 | * Implementation of distance models. |
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7 | */ |
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8 | #include "al_siteconfig.h" |
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9 | |
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10 | #include <math.h> |
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11 | |
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12 | #include "al_distance.h" |
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13 | #include "al_main.h" |
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14 | |
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15 | /* |
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16 | * No distance attenuation. Which means we return 1.0 for all values. |
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17 | */ |
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18 | static ALfloat |
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19 | noAttenuation( UNUSED(ALfloat distance), |
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20 | UNUSED(ALfloat rolloffFactor), |
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21 | UNUSED(ALfloat referenceDistance), |
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22 | UNUSED(ALfloat maxDistance)) |
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23 | { |
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24 | return 1.0f; |
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25 | } |
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26 | |
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27 | static ALfloat |
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28 | inverseDistance( ALfloat distance, |
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29 | ALfloat rolloffFactor, |
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30 | ALfloat referenceDistance, |
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31 | UNUSED(ALfloat maxDistance)) |
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32 | { |
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33 | /* |
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34 | * At this distance, the gain formula has a singularity and smaller |
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35 | * distances would result in a negative gain. In these cases, the spec |
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36 | * explicitly requires "no attenuation". |
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37 | */ |
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38 | ALfloat critDist = referenceDistance + (rolloffFactor * (distance - referenceDistance)); |
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39 | if (critDist <= 0.0f) { |
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40 | return 1.0f; |
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41 | } |
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42 | |
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43 | return referenceDistance / critDist; |
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44 | } |
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45 | |
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46 | static ALfloat |
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47 | inverseDistanceClamped( ALfloat distance, |
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48 | ALfloat rolloffFactor, |
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49 | ALfloat referenceDistance, |
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50 | ALfloat maxDistance ) |
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51 | { |
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52 | ALfloat critDist; |
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53 | |
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54 | if (maxDistance <= referenceDistance) { |
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55 | return 1.0; |
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56 | } |
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57 | |
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58 | /* distance = MAX( distance, referenceDistance ) */ |
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59 | if( distance < referenceDistance ) { |
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60 | distance = referenceDistance; |
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61 | } |
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62 | |
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63 | /* distance = MIN( distance, maxDistance ) */ |
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64 | if( distance > maxDistance ) { |
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65 | distance = maxDistance; |
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66 | } |
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67 | |
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68 | /* |
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69 | * At this distance, the gain formula has a singularity and smaller |
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70 | * distances would result in a negative gain. In these cases, the spec |
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71 | * explicitly requires "no attenuation". |
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72 | */ |
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73 | critDist = referenceDistance + (rolloffFactor * (distance - referenceDistance)); |
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74 | if (critDist <= 0.0f) { |
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75 | return 1.0f; |
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76 | } |
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77 | |
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78 | return referenceDistance / critDist; |
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79 | } |
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80 | |
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81 | static ALfloat |
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82 | linearDistance( ALfloat distance, |
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83 | ALfloat rolloffFactor, |
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84 | ALfloat referenceDistance, |
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85 | ALfloat maxDistance) |
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86 | { |
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87 | if (maxDistance <= referenceDistance) { |
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88 | return 1.0f; |
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89 | } |
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90 | |
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91 | return 1.0f - rolloffFactor * (distance - referenceDistance) / (maxDistance - referenceDistance); |
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92 | } |
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93 | |
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94 | static ALfloat |
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95 | linearDistanceClamped( ALfloat distance, |
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96 | ALfloat rolloffFactor, |
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97 | ALfloat referenceDistance, |
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98 | ALfloat maxDistance) |
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99 | { |
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100 | if (maxDistance <= referenceDistance) { |
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101 | return 1.0f; |
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102 | } |
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103 | |
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104 | /* distance = MAX( distance, referenceDistance ) */ |
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105 | if( distance < referenceDistance ) { |
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106 | distance = referenceDistance; |
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107 | } |
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108 | |
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109 | /* distance = MIN( distance, maxDistance ) */ |
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110 | if( distance > maxDistance ) { |
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111 | distance = maxDistance; |
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112 | } |
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113 | |
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114 | return 1.0f - rolloffFactor * (distance - referenceDistance) / (maxDistance - referenceDistance); |
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115 | } |
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116 | |
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117 | static ALfloat |
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118 | exponentDistance( ALfloat distance, |
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119 | ALfloat rolloffFactor, |
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120 | ALfloat referenceDistance, |
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121 | UNUSED(ALfloat maxDistance)) |
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122 | { |
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123 | ALfloat quotient; |
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124 | |
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125 | if (referenceDistance == 0.0f) { |
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126 | return 1.0f; |
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127 | } |
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128 | |
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129 | quotient = distance / referenceDistance; |
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130 | if (quotient == 0.0f) { |
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131 | return 1.0f; |
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132 | } |
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133 | |
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134 | return (ALfloat)pow(quotient, -rolloffFactor); |
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135 | } |
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136 | |
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137 | static ALfloat |
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138 | exponentDistanceClamped( ALfloat distance, |
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139 | ALfloat rolloffFactor, |
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140 | ALfloat referenceDistance, |
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141 | ALfloat maxDistance) |
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142 | { |
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143 | ALfloat quotient; |
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144 | |
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145 | if ((maxDistance <= referenceDistance) || (referenceDistance == 0.0f)) { |
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146 | return 1.0f; |
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147 | } |
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148 | |
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149 | /* distance = MAX( distance, referenceDistance ) */ |
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150 | if( distance < referenceDistance ) { |
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151 | distance = referenceDistance; |
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152 | } |
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153 | |
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154 | /* distance = MIN( distance, maxDistance ) */ |
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155 | if( distance > maxDistance ) { |
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156 | distance = maxDistance; |
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157 | } |
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158 | |
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159 | quotient = distance / referenceDistance; |
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160 | if (quotient == 0.0f) { |
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161 | return 1.0f; |
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162 | } |
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163 | |
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164 | return (ALfloat)pow(quotient, -rolloffFactor); |
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165 | } |
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166 | |
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167 | void |
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168 | _alUpdateDistanceModel( AL_context *cc ) |
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169 | { |
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170 | switch( cc->distance_model) { |
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171 | case AL_NONE: |
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172 | cc->distance_func = noAttenuation; |
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173 | break; |
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174 | case AL_INVERSE_DISTANCE: |
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175 | cc->distance_func = inverseDistance; |
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176 | break; |
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177 | case AL_INVERSE_DISTANCE_CLAMPED: |
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178 | cc->distance_func = inverseDistanceClamped; |
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179 | break; |
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180 | case AL_LINEAR_DISTANCE: |
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181 | cc->distance_func = linearDistance; |
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182 | break; |
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183 | case AL_LINEAR_DISTANCE_CLAMPED: |
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184 | cc->distance_func = linearDistanceClamped; |
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185 | break; |
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186 | case AL_EXPONENT_DISTANCE: |
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187 | cc->distance_func = exponentDistance; |
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188 | break; |
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189 | case AL_EXPONENT_DISTANCE_CLAMPED: |
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190 | cc->distance_func = exponentDistanceClamped; |
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191 | break; |
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192 | default: |
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193 | /* should never happen, just to be safe */ |
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194 | cc->distance_func = inverseDistanceClamped; |
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195 | break; |
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196 | } |
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197 | } |
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