title: What is the meaning of skin indices and skin weights?
body: <p>This is undocumented, so I'm asking here. I'm trying to animate a mesh in JavaScript. I'm using Blender->Three.js exporter because it is convenient. I can't use Three.js itself because I was not able to figure out how to solve certain problems on it (rendering the normals and depth informations of a scene with animated meshes to a buffer). So, how do you read the "skinIndices" and "skinWeights" properties that get exported from Blender to Three.js? What do they mean, and what are they roles when calculating the position of the vertices on the animations?</p>
  
  <pre><code>"bones" : [
      {"parent":-1,"name":"pelvis","pos":[-3.52132e-08,0.0410043,0.880063],"rotq":[0,0,0,1]},
      {"parent":0,"name":"thigh.L","pos":[0.0878887,0.00522349,0.102822],"rotq":[0,0,0,1]},
      {"parent":1,"name":"shin.L","pos":[0.103679,0.00638392,-0.445744],"rotq":[0,0,0,1]},
      {"parent":2,"name":"foot.L","pos":[0.0655578,0.0194668,-0.418675],"rotq":[0,0,0,1]},
      {"parent":3,"name":"toe.L","pos":[0.0280578,-0.107185,-0.0704246],"rotq":[0,0,0,1]},
      {"parent":3,"name":"heel.L","pos":[3.58224e-05,0.036576,-0.0885088],"rotq":[0,0,0,1]},
      {"parent":0,"name":"thigh.R","pos":[-0.0878888,0.00522352,0.102822],"rotq":[0,0,0,1]},
      {"parent":6,"name":"shin.R","pos":[-0.103679,0.00638412,-0.445745],"rotq":[0,0,0,1]},
      {"parent":7,"name":"foot.R","pos":[-0.0655576,0.0194677,-0.418675],"rotq":[0,0,0,1]},
      {"parent":8,"name":"toe.R","pos":[-0.0280577,-0.107185,-0.0704248],"rotq":[0,0,0,1]},
      {"parent":8,"name":"heel.R","pos":[-3.57926e-05,0.036576,-0.0885083],"rotq":[0,0,0,1]},
      {"parent":0,"name":"stomach","pos":[5.37268e-09,-0.008465,0.121596],"rotq":[0,0,0,1]},
      {"parent":11,"name":"chest","pos":[1.94616e-08,0.0538289,0.269019],"rotq":[0,0,0,1]},
      {"parent":12,"name":"upper_arm.L","pos":[0.160045,-0.010388,0.159844],"rotq":[0,0,0,1]},
      {"parent":13,"name":"forearm.L","pos":[0.165089,0.0102809,-0.232678],"rotq":[0,0,0,1]},
      {"parent":14,"name":"hand.L","pos":[0.0980782,-0.0148839,-0.245313],"rotq":[0,0,0,1]},
      {"parent":15,"name":"index.L.001","pos":[0.019191,-0.040475,-0.0743723],"rotq":[0,0,0,1]},
      {"parent":16,"name":"index.L.002","pos":[-0.00562334,-0.00824448,-0.0310695],"rotq":[0,0,0,1]},
      {"parent":17,"name":"index.L.003","pos":[-0.00953785,-0.00126594,-0.0192741],"rotq":[0,0,0,1]},
      {"parent":15,"name":"middle.L.001","pos":[0.0191911,-0.0188201,-0.0769786],"rotq":[0,0,0,1]},
      {"parent":19,"name":"middle.L.002","pos":[0.00288424,-0.00695575,-0.0326532],"rotq":[0,0,0,1]},
      {"parent":20,"name":"middle.L.003","pos":[-0.0111618,-0.00550338,-0.0242877],"rotq":[0,0,0,1]},
      {"parent":15,"name":"ring.L.001","pos":[0.0186397,0.00194495,-0.0777299],"rotq":[0,0,0,1]},
      {"parent":22,"name":"ring.L.002","pos":[0.00393239,-0.00062982,-0.0309386],"rotq":[0,0,0,1]},
      {"parent":23,"name":"ring.L.003","pos":[-0.00873661,-0.00165674,-0.024165],"rotq":[0,0,0,1]},
      {"parent":15,"name":"pinky.L.001","pos":[0.0191911,0.02271,-0.0758559],"rotq":[0,0,0,1]},
      {"parent":25,"name":"pinky.L.002","pos":[-0.0057596,0.0014303,-0.0236881],"rotq":[0,0,0,1]},
      {"parent":26,"name":"pinky.L.003","pos":[-0.00877053,-0.0020119,-0.0195478],"rotq":[0,0,0,1]},
      {"parent":15,"name":"thumb.L.001","pos":[-0.0073517,-0.0318671,-0.0156776],"rotq":[0,0,0,1]},
      {"parent":28,"name":"thumb.L.002","pos":[-0.00941652,-0.0166059,-0.0179188],"rotq":[0,0,0,1]},
      {"parent":29,"name":"thumb.L.003","pos":[-0.0081799,-0.0129757,-0.0276645],"rotq":[0,0,0,1]},
      {"parent":12,"name":"upper_arm.R","pos":[-0.160044,-0.010388,0.159844],"rotq":[0,0,0,1]},
      {"parent":31,"name":"forearm.R","pos":[-0.165089,0.0102809,-0.232679],"rotq":[0,0,0,1]},
      {"parent":32,"name":"hand.R","pos":[-0.0980774,-0.0148839,-0.245313],"rotq":[0,0,0,1]},
      {"parent":33,"name":"index.R.001","pos":[-0.0185038,-0.0404748,-0.0743726],"rotq":[0,0,0,1]},
      {"parent":34,"name":"index.R.002","pos":[0.00562337,-0.00824449,-0.0310695],"rotq":[0,0,0,1]},
      {"parent":35,"name":"index.R.003","pos":[0.00953785,-0.00126596,-0.0192741],"rotq":[0,0,0,1]},
      {"parent":33,"name":"middle.R.001","pos":[-0.0185038,-0.0188199,-0.0769789],"rotq":[0,0,0,1]},
      {"parent":37,"name":"middle.R.002","pos":[-0.00288421,-0.00695577,-0.0326532],"rotq":[0,0,0,1]},
      {"parent":38,"name":"middle.R.003","pos":[0.0111619,-0.00550339,-0.0242877],"rotq":[0,0,0,1]},
      {"parent":33,"name":"ring.R.001","pos":[-0.0179525,0.00194514,-0.0777302],"rotq":[0,0,0,1]},
      {"parent":40,"name":"ring.R.002","pos":[-0.00393245,-0.000629827,-0.0309386],"rotq":[0,0,0,1]},
      {"parent":41,"name":"ring.R.003","pos":[0.00873658,-0.00165676,-0.024165],"rotq":[0,0,0,1]},
      {"parent":33,"name":"pinky.R.001","pos":[-0.0185039,0.0227101,-0.0758562],"rotq":[0,0,0,1]},
      {"parent":43,"name":"pinky.R.002","pos":[0.0057596,0.00143027,-0.0236881],"rotq":[0,0,0,1]},
      {"parent":44,"name":"pinky.R.003","pos":[0.00877053,-0.00201192,-0.0195478],"rotq":[0,0,0,1]},
      {"parent":33,"name":"thumb.R.001","pos":[0.00803882,-0.0318669,-0.0156779],"rotq":[0,0,0,1]},
      {"parent":46,"name":"thumb.R.002","pos":[0.00941664,-0.0166059,-0.0179188],"rotq":[0,0,0,1]},
      {"parent":47,"name":"thumb.R.003","pos":[0.00817987,-0.0129757,-0.0276645],"rotq":[0,0,0,1]},
      {"parent":12,"name":"neck","pos":[1.6885e-08,-0.0164749,0.225555],"rotq":[0,0,0,1]},
      {"parent":49,"name":"head","pos":[0.000806741,-0.0273245,0.0637051],"rotq":[0,0,0,1]}],
  
  "skinIndices" : [
          11,0,11,0,1,11,11,0,0,11,0,11,1,11,1,11,0,11,11,0,11,0,11,0,1,11,11,0,11,0,0,11,1,11,1,11,0,11,0,11,0,11,12,0,0,11,0,11,
          0,11,12,0,12,0,11,0,11,0,11,0,12,0,11,0,11,0,11,0,12,0,12,11,11,0,11,0,12,13,11,0,0,11,11,0,12,13,12,13,0,11,12,13,12,0,
          12,0,13,12,13,12,12,13,12,0,12,13,13,12,12,13,12,13,13,12,13,0,12,13,12,0,12,13,13,0,12,0,13,0,0,13,13,0,13,0,0,13,0,13,
          13,0,13,0,0,13,13,12,13,12,13,12,13,0,13,0,13,0,13,12,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,0,13,
          (... too big)]
  
  "skinWeights" : [
      0.454566,0.443267,0.456435,0.4405,0.568642,0.331477,0.452697,0.446034,0.600277,0.577654,0.603738,0.578153,0.557686,0.334716,
      0.579597,0.328238,0.596817,0.577156,0.481496,0.447683,0.604872,0.59171,0.466162,0.448242,0.567426,0.35812,0.49683,0.447124,
      0.618979,0.590887,0.592533,0.590764,0.578989,0.341559,0.555862,0.37468,0.477411,0.438341,0.617349,0.569542,0.454728,0.432345,
      0.401061,0.337472,0.500093,0.444338,0.633534,0.572105,0.601164,0.56698,0.388198,0.308292,0.413925,0.366652,0.449179,0.424051,
      0.618298,0.58735,0.458406,0.430254,0.473939,0,0.439952,0.417849,0.605333,0.579977,0.631263,0.594722,0.517687,0,0.430191,0.274572,
      (... too big)]
  
  
  "animations" : [
      {"name":"ArmatureAction",
      "fps":24,
      "length":0.625,
      "hierarchy":
      [{"parent":-1,"keys":[
          {"time":0,"pos":[-3.52132e-08,0.0410043,0.880063],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[-3.52132e-08,0.0410043,0.880063]},
          {"time":0.625,"pos":[-3.52132e-08,0.0410043,0.880063],"rot":[0,0,0,1],"scl":[1,1,1]}]
      },
      {"parent":0,"keys":[
          {"time":0,"pos":[0.0878887,0.00522349,0.102822],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[0.0878887,0.00522349,0.102822],"rot":[-0.36166,-1.53668e-08,-7.05768e-10,0.93231]},
          {"time":0.625,"pos":[0.0878887,0.00522349,0.102822],"rot":[0,0,0,1],"scl":[1,1,1]}
      ]},
      {"parent":1,"keys":[
          {"time":0,"pos":[0.103679,0.00638392,-0.445744],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[0.103679,0.00638392,-0.445744]},
          {"time":0.625,"pos":[0.103679,0.00638392,-0.445744],"rot":[0,0,0,1],"scl":[1,1,1]}
      ]},
      {"parent":2,"keys":[
          {"time":0,"pos":[0.0655578,0.0194668,-0.418675],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[0.0655578,0.0194668,-0.418675]},
          {"time":0.625,"pos":[0.0655578,0.0194668,-0.418675],"rot":[0,0,0,1],"scl":[1,1,1]}
      ]},
      {"parent":3,"keys":[
          {"time":0,"pos":[0.0280578,-0.107185,-0.0704246],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[0.0280578,-0.107185,-0.0704246]},
          {"time":0.625,"pos":[0.0280578,-0.107185,-0.0704246],"rot":[0,0,0,1],"scl":[1,1,1]}
      ]},
      {"parent":4,"keys":[
          {"time":0,"pos":[3.58149e-05,0.036576,-0.0885088],"rot":[0,0,0,1],"scl":[1,1,1]},
          {"time":0.291667,"pos":[3.58149e-05,0.036576,-0.0885088]},
          {"time":0.625,"pos":[3.58149e-05,0.036576,-0.0885088],"rot":[0,0,0,1],"scl":[1,1,1]}
      ]},
  </code></pre>