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1 #+title: Simulated Sense of Touch
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2 #+author: Robert McIntyre
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3 #+email: rlm@mit.edu
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4 #+description: Simulated touch for AI research using JMonkeyEngine and clojure.
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5 #+keywords: simulation, tactile sense, jMonkeyEngine3, clojure
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6 #+SETUPFILE: ../../aurellem/org/setup.org
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7 #+INCLUDE: ../../aurellem/org/level-0.org
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8
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9
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10
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11 * Touch
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12
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13 Touch is critical to navigation and spatial reasoning and as such I
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14 need a simulated version of it to give to my AI creatures.
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15
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16 However, touch in my virtual can not exactly correspond to human touch
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17 because my creatures are made out of completely rigid segments that
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18 don't deform like human skin.
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19
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20 Human skin has a wide array of touch sensors, each of which speciliaze
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21 in detecting different vibrational modes and pressures. These sensors
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22 can integrate a vast expanse of skin (i.e. your entire palm), or a
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23 tiny patch of skin at the tip of your finger. The hairs of the skin
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24 help detect objects before they even come into contact with the skin
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25 proper.
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26
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27 Instead of measuring deformation or vibration, I surround each rigid
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28 part with a plenitude of hair-like objects which do not interact with
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29 the physical world. Physical objects can pass through them with no
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30 effect. The hairs are able to measure contact with other objects, and
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31 constantly report how much of their extent is covered. So, even though
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32 the creature's body parts do not deform, the hairs create a margin
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33 around those body parts which achieves a sense of touch which is a
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34 hybrid between a human's sense of deformation and sense from hairs.
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35
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36 Implementing touch in jMonkeyEngine follows a different techinal route
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37 than vision and hearing. Those two senses piggybacked off
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38 jMonkeyEngine's 3D audio and video rendering subsystems. To simulate
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39 Touch, I use jMonkeyEngine's physics system to execute many small
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40 collision detections, one for each "hair". The placement of the
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41 "hairs" is determined by a UV-mapped image which shows where each hair
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42 should be on the 3D surface of the body.
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43
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44
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45 * Defining Touch Meta-Data in Blender
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46
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47 Each geometry can have a single UV map which describes the position
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48 and length of the "hairs" which will constitute its sense of
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49 touch. This image path is stored under the "touch" key. The image
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50 itself is grayscale, with black meaning a hair length of 0 (no hair is
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51 present) and white meaning a hair length of =scale=, which is a float
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52 stored under the key "scale". If the pixel is gray then the resultant
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53 hair length is linearly interpolated between 0 and =scale=.
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54
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55 #+name: meta-data
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56 #+begin_src clojure
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57 (defn tactile-sensor-profile
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58 "Return the touch-sensor distribution image in BufferedImage format,
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59 or nil if it does not exist."
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60 [#^Geometry obj]
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61 (if-let [image-path (meta-data obj "touch")]
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62 (load-image image-path)))
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63
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64 (defn tactile-scale
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65 "Return the maximum length of a hair. All hairs are scalled between
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66 0.0 and this length, depending on their color. Black is 0, and
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67 white is maximum length, and everything in between is scalled
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68 linearlly. Default scale is 0.01 jMonkeyEngine units."
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69 [#^Geometry obj]
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70 (if-let [scale (meta-data obj "scale")]
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71 scale 0.1))
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72 #+end_src
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73
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74 ** TODO add image showing example touch-uv map
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75 ** TODO add metadata display for worm
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76
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77
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78 * Skin Creation
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79 * TODO get the actual lengths for each hair
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80
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81 #+begin_src clojure
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82 pixel-triangles
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83 xyz-triangles
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84 conversions (map triangles->affine-transform pixel-triangles
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85 xyz-triangles)
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86
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87 #+end_src
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88
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89 #+name: kernel
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90 #+begin_src clojure
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91 (in-ns 'cortex.touch)
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92
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93 (declare touch-topology touch-hairs set-ray)
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94
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95 (defn touch-kernel
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96 "Constructs a function which will return tactile sensory data from
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97 'geo when called from inside a running simulation"
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98 [#^Geometry geo]
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99 (let [[ray-reference-origins
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100 ray-reference-tips
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101 ray-lengths] (touch-hairs geo)
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102 current-rays (map (fn [] (Ray.)) ray-reference-origins)
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103 topology (touch-topology geo)]
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104 (if (empty? ray-reference-origins) nil
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105 (fn [node]
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106 (let [transform (.getWorldMatrix geo)]
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107 (dorun
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108 (map (fn [ray ref-origin ref-tip length]
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109 (set-ray ray transform ref-origin ref-tip length))
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110 current-rays ray-reference-origins
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111 ray-reference-tips ray-lengths))
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112 (vector
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113 topology
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114 (vec
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115 (for [ray current-rays]
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116 (do
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117 (let [results (CollisionResults.)]
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118 (.collideWith node ray results)
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119 (let [touch-objects
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120 (filter #(not (= geo (.getGeometry %)))
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121 results)]
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122 [(if (empty? touch-objects)
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123 (.getLimit ray)
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124 (.getDistance (first touch-objects)))
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125 (.getLimit ray)])))))))))))
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126
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127 (defn touch-kernel*
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128 "Returns a function which returns tactile sensory data when called
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129 inside a running simulation."
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130 [#^Geometry geo]
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131 (let [feeler-coords (feeler-coordinates geo)
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132 tris (triangles geo)
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133 limit (tactile-scale geo)]
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134 (if (empty? (touch-topology geo))
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135 nil
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136 (fn [node]
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137 (let [sensor-origins
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138 (map
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139 #(map (partial local-to-world geo) %)
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140 feeler-coords)
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141 triangle-normals
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142 (map (partial get-ray-direction geo)
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143 tris)
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144 rays
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145 (flatten
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146 (map (fn [origins norm]
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147 (map #(doto (Ray. % norm)
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148 (.setLimit limit)) origins))
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149 sensor-origins triangle-normals))]
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150 (vector
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151 (touch-topology geo)
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152 (vec
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153 (for [ray rays]
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154 (do
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155 (let [results (CollisionResults.)]
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156 (.collideWith node ray results)
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157 (let [touch-objects
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158 (filter #(not (= geo (.getGeometry %)))
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159 results)]
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160 [(if (empty? touch-objects)
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161 limit (.getDistance (first touch-objects)))
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162 limit])))))))))))
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163
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164 (defn touch!
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165 "Endow the creature with the sense of touch. Returns a sequence of
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166 functions, one for each body part with a tactile-sensor-proile,
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167 each of which when called returns sensory data for that body part."
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168 [#^Node creature]
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169 (filter
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170 (comp not nil?)
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171 (map touch-kernel
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172 (filter #(isa? (class %) Geometry)
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173 (node-seq creature)))))
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174 #+end_src
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175
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176 * Visualizing Touch
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177 #+name: visualization
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178 #+begin_src clojure
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179 (in-ns 'cortex.touch)
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180
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181 (defn touch->gray
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182 "Convert a pair of [distance, max-distance] into a grayscale pixel"
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183 [distance max-distance]
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184 (gray
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185 (- 255
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186 (rem
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187 (int
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188 (* 255 (/ distance max-distance)))
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189 256))))
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190
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191 (defn view-touch
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192 "Creates a function which accepts a list of touch sensor-data and
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193 displays each element to the screen."
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194 []
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195 (view-sense
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196 (fn
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197 [[coords sensor-data]]
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198 (let [image (points->image coords)]
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199 (dorun
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200 (for [i (range (count coords))]
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201 (.setRGB image ((coords i) 0) ((coords i) 1)
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202 (apply touch->gray (sensor-data i)))))
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203 image))))
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204 #+end_src
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205
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206
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207
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208 * Triangle Manipulation Functions
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209
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210 The rigid bodies which make up a creature have an underlying
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211 =Geometry=, which is a =Mesh= plus a =Material= and other important
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212 data involved with displaying the body.
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213
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214 A =Mesh= is composed of =Triangles=, and each =Triangle= has three
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215 verticies which have coordinates in XYZ space and UV space.
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216
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217 Here, =(triangles)= gets all the triangles which compose a mesh, and
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218 =(triangle-UV-coord)= returns the the UV coordinates of the verticies
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219 of a triangle.
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220
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221 #+name: triangles-1
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222 #+begin_src clojure
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223 (defn triangles
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224 "Return a sequence of all the Triangles which compose a given
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225 Geometry."
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226 [#^Geometry geom]
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227 (let
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228 [mesh (.getMesh geom)
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229 triangles (transient [])]
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230 (dorun
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231 (for [n (range (.getTriangleCount mesh))]
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232 (let [tri (Triangle.)]
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233 (.getTriangle mesh n tri)
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234 ;; (.calculateNormal tri)
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235 ;; (.calculateCenter tri)
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236 (conj! triangles tri))))
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237 (persistent! triangles)))
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238
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239 (defn mesh-triangle
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240 "Get the triangle specified by triangle-index from the mesh within
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241 bounds."
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242 [#^Mesh mesh triangle-index]
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243 (let [scratch (Triangle.)]
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244 (.getTriangle mesh triangle-index scratch)
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245 scratch))
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246
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247 (defn triangle-vertex-indices
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248 "Get the triangle vertex indices of a given triangle from a given
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249 mesh."
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250 [#^Mesh mesh triangle-index]
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251 (let [indices (int-array 3)]
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252 (.getTriangle mesh triangle-index indices)
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253 (vec indices)))
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254
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255 (defn vertex-UV-coord
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256 "Get the UV-coordinates of the vertex named by vertex-index"
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257 [#^Mesh mesh vertex-index]
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258 (let [UV-buffer
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259 (.getData
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260 (.getBuffer
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261 mesh
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262 VertexBuffer$Type/TexCoord))]
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263 [(.get UV-buffer (* vertex-index 2))
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264 (.get UV-buffer (+ 1 (* vertex-index 2)))]))
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265
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266 (defn triangle-UV-coord
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267 "Get the UV-cooridnates of the triangle's verticies."
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268 [#^Mesh mesh width height triangle-index]
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269 (map (fn [[u v]] (vector (* width u) (* height v)))
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270 (map (partial vertex-UV-coord mesh)
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271 (triangle-vertex-indices mesh triangle-index))))
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272 #+end_src
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273
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274 * Schrapnel Conversion Functions
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275
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276 It is convienent to treat a =Triangle= as a sequence of verticies, and
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277 a =Vector2f= and =Vector3f= as a sequence of floats. These conversion
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278 functions make this easy. If these classes implemented =Iterable= then
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279 this code would not be necessary. Hopefully they will in the future.
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280
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281 #+name: triangles-2
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282 #+begin_src clojure
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283 (defn triangle-seq [#^Triangle tri]
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284 [(.get1 tri) (.get2 tri) (.get3 tri)])
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285
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286 (defn vector3f-seq [#^Vector3f v]
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287 [(.getX v) (.getY v) (.getZ v)])
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288
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289 (defn point->vector2f [[u v]]
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290 (Vector2f. u v))
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291
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292 (defn vector2f->vector3f [v]
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293 (Vector3f. (.getX v) (.getY v) 0))
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294
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295 (defn map-triangle [f #^Triangle tri]
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296 (Triangle.
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297 (f 0 (.get1 tri))
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298 (f 1 (.get2 tri))
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299 (f 2 (.get3 tri))))
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300
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301 (defn points->triangle
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302 "Convert a list of points into a triangle."
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303 [points]
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304 (apply #(Triangle. %1 %2 %3)
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305 (map (fn [point]
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306 (let [point (vec point)]
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307 (Vector3f. (get point 0 0)
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308 (get point 1 0)
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309 (get point 2 0))))
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310 (take 3 points))))
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311 #+end_src
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312
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313 * Triangle Affine Transforms
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314
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315 The position of each hair is stored in a 2D image in UV
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316 coordinates. To place the hair in 3D space we must convert from UV
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317 coordinates to XYZ coordinates. Each =Triangle= has coordinates in
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318 both UV-space and XYZ-space, which defines a unique [[http://mathworld.wolfram.com/AffineTransformation.html ][Affine Transform]]
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319 for translating any coordinate within the UV triangle to the
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320 cooresponding coordinate in the XYZ triangle.
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321
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322 #+name: triangles-3
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323 #+begin_src clojure
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324 (defn triangle->matrix4f
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325 "Converts the triangle into a 4x4 matrix: The first three columns
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326 contain the vertices of the triangle; the last contains the unit
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327 normal of the triangle. The bottom row is filled with 1s."
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328 [#^Triangle t]
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329 (let [mat (Matrix4f.)
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330 [vert-1 vert-2 vert-3]
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331 ((comp vec map) #(.get t %) (range 3))
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332 unit-normal (do (.calculateNormal t)(.getNormal t))
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333 vertices [vert-1 vert-2 vert-3 unit-normal]]
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334 (dorun
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335 (for [row (range 4) col (range 3)]
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336 (do
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337 (.set mat col row (.get (vertices row)col))
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338 (.set mat 3 row 1))))
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339 mat))
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340
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341 (defn triangle-transformation
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342 "Returns the affine transformation that converts each vertex in the
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343 first triangle into the corresponding vertex in the second
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344 triangle."
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345 [#^Triangle tri-1 #^Triangle tri-2]
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346 (.mult
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347 (triangle->matrix4f tri-2)
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348 (.invert (triangle->matrix4f tri-1))))
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349 #+end_src
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350
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351 * Triangle Boundaries
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352
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353 For efficiency's sake I will divide the UV-image into small squares
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354 which inscribe each UV-triangle, then extract the points which lie
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355 inside the triangle and map them to 3D-space using
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356 =(triangle-transform)= above. To do this I need a function,
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357 =(inside-triangle?)=, which determines whether a point is inside a
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358 triangle in 2D UV-space.
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359
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360 #+name: triangles-4
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361 #+begin_src clojure
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362 (defn convex-bounds
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363 "Returns the smallest square containing the given vertices, as a
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364 vector of integers [left top width height]."
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365 [uv-verts]
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366 (let [xs (map first uv-verts)
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367 ys (map second uv-verts)
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368 x0 (Math/floor (apply min xs))
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369 y0 (Math/floor (apply min ys))
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370 x1 (Math/ceil (apply max xs))
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371 y1 (Math/ceil (apply max ys))]
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372 [x0 y0 (- x1 x0) (- y1 y0)]))
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373
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374 (defn same-side?
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375 "Given the points p1 and p2 and the reference point ref, is point p
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376 on the same side of the line that goes through p1 and p2 as ref is?"
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377 [p1 p2 ref p]
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378 (<=
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379 0
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380 (.dot
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381 (.cross (.subtract p2 p1) (.subtract p p1))
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382 (.cross (.subtract p2 p1) (.subtract ref p1)))))
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383
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384 (defn inside-triangle?
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385 "Is the point inside the triangle?"
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386 {:author "Dylan Holmes"}
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387 [#^Triangle tri #^Vector3f p]
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388 (let [[vert-1 vert-2 vert-3] (triangle-seq tri)]
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389 (and
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390 (same-side? vert-1 vert-2 vert-3 p)
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391 (same-side? vert-2 vert-3 vert-1 p)
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392 (same-side? vert-3 vert-1 vert-2 p))))
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393 #+end_src
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394
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395
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396 * Sensor Related Functions
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397
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398 These functions analyze the touch-sensor-profile image convert the
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399 location of each touch sensor from pixel coordinates to UV-coordinates
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400 and XYZ-coordinates.
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401
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402 #+name: sensors
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403 #+begin_src clojure
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404 (defn sensors-in-triangle
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405 "Locate the touch sensors in the triangle, returning a map of their
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406 UV and geometry-relative coordinates."
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407 [image mesh tri-index]
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408 (let [width (.getWidth image)
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409 height (.getHeight image)
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410 UV-vertex-coords (triangle-UV-coord mesh width height tri-index)
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411 bounds (convex-bounds UV-vertex-coords)
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412
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413 cutout-triangle (points->triangle UV-vertex-coords)
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414 UV-sensor-coords
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415 (filter (comp (partial inside-triangle? cutout-triangle)
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416 (fn [[u v]] (Vector3f. u v 0)))
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417 (white-coordinates image bounds))
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418 UV->geometry (triangle-transformation
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419 cutout-triangle
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420 (mesh-triangle mesh tri-index))
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421 geometry-sensor-coords
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422 (map (fn [[u v]] (.mult UV->geometry (Vector3f. u v 0)))
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423 UV-sensor-coords)]
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424 {:UV UV-sensor-coords :geometry geometry-sensor-coords}))
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425
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426 (defn-memo locate-feelers
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427 "Search the geometry's tactile UV profile for touch sensors,
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428 returning their positions in geometry-relative coordinates."
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429 [#^Geometry geo]
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430 (let [mesh (.getMesh geo)
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431 num-triangles (.getTriangleCount mesh)]
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432 (if-let [image (tactile-sensor-profile geo)]
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433 (map
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434 (partial sensors-in-triangle image mesh)
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435 (range num-triangles))
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436 (repeat (.getTriangleCount mesh) {:UV nil :geometry nil}))))
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437
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438 (defn-memo touch-topology
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439 "Return a sequence of vectors of the form [x y] describing the
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440 \"topology\" of the tactile sensors. Points that are close together
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441 in the touch-topology are generally close together in the simulation."
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442 [#^Gemoetry geo]
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443 (vec (collapse (reduce concat (map :UV (locate-feelers geo))))))
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444
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445 (defn-memo feeler-coordinates
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446 "The location of the touch sensors in world-space coordinates."
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447 [#^Geometry geo]
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448 (vec (map :geometry (locate-feelers geo))))
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449 #+end_src
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450
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451 * Physics Collision Objects
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452
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453 The "hairs" are actually =Rays= which extend from a point on a
|
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454 =Triangle= in the =Mesh= normal to the =Triangle's= surface.
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455
|
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456 #+name: rays
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457 #+begin_src clojure
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458 (defn get-ray-origin
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459 "Return the origin which a Ray would have to have to be in the exact
|
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460 center of a particular Triangle in the Geometry in World
|
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461 Coordinates."
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462 [geom tri]
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463 (let [new (Vector3f.)]
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464 (.calculateCenter tri)
|
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465 (.localToWorld geom (.getCenter tri) new) new))
|
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466
|
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467 (defn get-ray-direction
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468 "Return the direction which a Ray would have to have to be to point
|
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469 normal to the Triangle, in coordinates relative to the center of the
|
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470 Triangle."
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471 [geom tri]
|
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472 (let [n+c (Vector3f.)]
|
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473 (.calculateNormal tri)
|
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474 (.calculateCenter tri)
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475 (.localToWorld
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476 geom
|
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477 (.add (.getCenter tri) (.getNormal tri)) n+c)
|
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478 (.subtract n+c (get-ray-origin geom tri))))
|
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479 #+end_src
|
rlm@226
|
480 * Headers
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481
|
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482 #+name: touch-header
|
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483 #+begin_src clojure
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rlm@226
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484 (ns cortex.touch
|
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485 "Simulate the sense of touch in jMonkeyEngine3. Enables any Geometry
|
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486 to be outfitted with touch sensors with density determined by a UV
|
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487 image. In this way a Geometry can know what parts of itself are
|
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488 touching nearby objects. Reads specially prepared blender files to
|
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489 construct this sense automatically."
|
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|
490 {:author "Robert McIntyre"}
|
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|
491 (:use (cortex world util sense))
|
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|
492 (:use clojure.contrib.def)
|
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|
493 (:import (com.jme3.scene Geometry Node Mesh))
|
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494 (:import com.jme3.collision.CollisionResults)
|
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495 (:import com.jme3.scene.VertexBuffer$Type)
|
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496 (:import (com.jme3.math Triangle Vector3f Vector2f Ray Matrix4f)))
|
rlm@226
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497 #+end_src
|
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498
|
rlm@232
|
499 * Adding Touch to the Worm
|
rlm@232
|
500
|
rlm@232
|
501 #+name: test-touch
|
rlm@232
|
502 #+begin_src clojure
|
rlm@232
|
503 (ns cortex.test.touch
|
rlm@232
|
504 (:use (cortex world util sense body touch))
|
rlm@232
|
505 (:use cortex.test.body))
|
rlm@232
|
506
|
rlm@232
|
507 (cortex.import/mega-import-jme3)
|
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|
508
|
rlm@232
|
509 (defn test-touch []
|
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|
510 (let [the-worm (doto (worm) (body!))
|
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|
511 touch (touch! the-worm)
|
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|
512 touch-display (view-touch)]
|
rlm@232
|
513 (world (nodify [the-worm (floor)])
|
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|
514 standard-debug-controls
|
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|
515
|
rlm@232
|
516 (fn [world]
|
rlm@232
|
517 (light-up-everything world))
|
rlm@232
|
518
|
rlm@232
|
519 (fn [world tpf]
|
rlm@232
|
520 (touch-display (map #(% (.getRootNode world)) touch))))))
|
rlm@232
|
521 #+end_src
|
rlm@228
|
522 * Source Listing
|
rlm@228
|
523 * Next
|
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|
524
|
rlm@228
|
525
|
rlm@226
|
526 * COMMENT Code Generation
|
rlm@39
|
527 #+begin_src clojure :tangle ../src/cortex/touch.clj
|
rlm@231
|
528 <<touch-header>>
|
rlm@231
|
529 <<meta-data>>
|
rlm@231
|
530 <<triangles-1>>
|
rlm@231
|
531 <<triangles-2>>
|
rlm@231
|
532 <<triangles-3>>
|
rlm@231
|
533 <<triangles-4>>
|
rlm@231
|
534 <<sensors>>
|
rlm@231
|
535 <<rays>>
|
rlm@231
|
536 <<kernel>>
|
rlm@231
|
537 <<visualization>>
|
rlm@0
|
538 #+end_src
|
rlm@0
|
539
|
rlm@232
|
540
|
rlm@68
|
541 #+begin_src clojure :tangle ../src/cortex/test/touch.clj
|
rlm@232
|
542 <<test-touch>>
|
rlm@39
|
543 #+end_src
|
rlm@39
|
544
|
rlm@0
|
545
|
rlm@0
|
546
|
rlm@0
|
547
|
rlm@32
|
548
|
rlm@32
|
549
|
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|
550
|