皮膚指數和皮膚重量是什麼意思？

Question

這是無證的，所以我在這裏問。我試圖在JavaScript中爲網格添加動畫。我使用Blender-> Three.js出口商，因爲它很方便。我無法使用Three.js本身，因爲我無法弄清楚如何解決某些問題（使用動畫網格渲染場景的法線和深度信息到緩衝區）。那麼，您如何閱讀從Blender導出爲Three.js的「skinIndices」和「skinWeights」屬性？他們的意思是什麼，他們在計算動畫頂點位置時的角色是什麼？

"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]} 
    ]}, 

Answer 1

每個頂點對應於一個皮膚指數，它對應於一個皮膚重量。皮膚索引是特定頂點受到影響的骨骼的索引（每個頂點只能屬於一個骨骼）。皮膚重量是骨在該頂點上的影響量。

Answer 2

skinIndices和skinWeights屬性是數組的數組（技術上，內部數組是三個對象的.js Vector4對象）。外部數組中的每個項都基於索引位置與網格中的每個頂點一一對應。

Here's the relevant JSONLoader code，對於從three.js所JSON模型文件這些屬性創建值：

if (json.skinWeights) { 

    for (var i = 0, l = json.skinWeights.length; i < l; i += influencesPerVertex) { 

     var x = json.skinWeights[ i ]; 
     var y = (influencesPerVertex > 1) ? json.skinWeights[ i + 1 ] : 0; 
     var z = (influencesPerVertex > 2) ? json.skinWeights[ i + 2 ] : 0; 
     var w = (influencesPerVertex > 3) ? json.skinWeights[ i + 3 ] : 0; 

     geometry.skinWeights.push(new Vector4(x, y, z, w)); 

    } 

} 

if (json.skinIndices) { 

    for (var i = 0, l = json.skinIndices.length; i < l; i += influencesPerVertex) { 

     var a = json.skinIndices[ i ]; 
     var b = (influencesPerVertex > 1) ? json.skinIndices[ i + 1 ] : 0; 
     var c = (influencesPerVertex > 2) ? json.skinIndices[ i + 2 ] : 0; 
     var d = (influencesPerVertex > 3) ? json.skinIndices[ i + 3 ] : 0; 

     geometry.skinIndices.push(new Vector4(a, b, c, d)); 

    } 
} 

The docs for the three.js Geometry object進行了更新以包含關於此信息[某些格式和兩個不一致的更正雷]：

就像skinWeights屬性一樣，skinIndices的值對應於幾何的頂點。每個頂點最多可以有4個關聯的骨骼。因此，如果您查看第一個頂點和第一個皮膚索引，它會告訴您與該頂點關聯的骨骼。例如，第一個頂點的值可以是(10.05, 30.10, 12.12)。然後，第一個皮膚指數的值可能爲(10, 2, 0, 0)。第一個皮膚重量可能爲(0.8, 0.2, 0, 0)。在影響這將採取第一個頂點，然後是骨骼mesh.bones[10]並應用它的80％的方式。然後它將採取骨頭mesh.bones[2]並應用它的20％的方式。接下來的兩個值的權重爲0，所以它們不會有任何影響。

在代碼中的另一個例子看起來是這樣的：

// e.g. 
geometry.skinIndices[15] = new THREE.Vector4( 0, 5, 9, 0); 
geometry.skinWeights[15] = new THREE.Vector4(0.2, 0.5, 0.3, 0); 

// corresponds with the following vertex 
geometry.vertices[15]; 

// these bones will be used like so: 
skeleton.bones[0]; // weight of 0.2 
skeleton.bones[5]; // weight of 0.5 
skeleton.bones[9]; // weight of 0.3 
skeleton.bones[10]; // weight of 0