<!
//  Skinning.slh
//  libraries/render-utils/src
//
//  Created by Sam Gateau on 10/5/15.
//  Copyright 2013 High Fidelity, Inc.
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
!>
<@if not SKINNING_SLH@>
<@def SKINNING_SLH@>

<@include graphics/ShaderConstants.h@>

<@func declareSkinning(USE_DUAL_QUATERNION_SKINNING, USE_NORMAL, USE_TANGENT)@>

const int MAX_CLUSTERS = 128;
const int INDICES_PER_VERTEX = 4;

LAYOUT_STD140(binding=GRAPHICS_BUFFER_SKINNING) uniform skinClusterBuffer {
    mat4 clusterMatrices[MAX_CLUSTERS];
};

<@if USE_DUAL_QUATERNION_SKINNING@>

mat4 dualQuatToMat4(vec4 real, vec4 dual) {
    float twoRealXSq = 2.0 * real.x * real.x;
    float twoRealYSq = 2.0 * real.y * real.y;
    float twoRealZSq = 2.0 * real.z * real.z;
    float twoRealXY = 2.0 * real.x * real.y;
    float twoRealXZ = 2.0 * real.x * real.z;
    float twoRealXW = 2.0 * real.x * real.w;
    float twoRealZW = 2.0 * real.z * real.w;
    float twoRealYZ = 2.0 * real.y * real.z;
    float twoRealYW = 2.0 * real.y * real.w;
    vec4 col0 = vec4(1.0 - twoRealYSq - twoRealZSq,
                     twoRealXY + twoRealZW,
                     twoRealXZ - twoRealYW,
                     0.0);
    vec4 col1 = vec4(twoRealXY - twoRealZW,
                     1.0 - twoRealXSq - twoRealZSq,
                     twoRealYZ + twoRealXW,
                     0.0);
    vec4 col2 = vec4(twoRealXZ + twoRealYW,
                     twoRealYZ - twoRealXW,
                     1.0 - twoRealXSq - twoRealYSq,
                     0.0);
    vec4 col3 = vec4(2.0 * (-dual.w * real.x + dual.x * real.w - dual.y * real.z + dual.z * real.y),
                     2.0 * (-dual.w * real.y + dual.x * real.z + dual.y * real.w - dual.z * real.x),
                     2.0 * (-dual.w * real.z - dual.x * real.y + dual.y * real.x + dual.z * real.w),
                     1.0);

    return mat4(col0, col1, col2, col3);
}

// dual quaternion linear blending
void evalSkinning(ivec4 skinClusterIndex, vec4 skinClusterWeight, vec4 inPosition, out vec4 skinnedPosition
<@if USE_NORMAL@>
    , vec3 inNormal, out vec3 skinnedNormal
<@endif@>
<@if USE_TANGENT@>
    , vec3 inTangent, out vec3 skinnedTangent
<@endif@>
) {

    // linearly blend scale and dual quaternion components
    vec4 sAccum = vec4(0.0, 0.0, 0.0, 0.0);
    vec4 rAccum = vec4(0.0, 0.0, 0.0, 0.0);
    vec4 dAccum = vec4(0.0, 0.0, 0.0, 0.0);
    vec4 cAccum = vec4(0.0, 0.0, 0.0, 0.0);
    vec4 polarityReference = clusterMatrices[skinClusterIndex[0]][1];
    for (int i = 0; i < INDICES_PER_VERTEX; i++) {
        mat4 clusterMatrix = clusterMatrices[(skinClusterIndex[i])];
        float clusterWeight = skinClusterWeight[i];

        vec4 scale = clusterMatrix[0];
        vec4 real = clusterMatrix[1];
        vec4 dual = clusterMatrix[2];
        vec4 cauterizedPos = clusterMatrix[3];

        // to ensure that we rotate along the shortest arc, reverse dual quaternions with negative polarity.
        float dqClusterWeight = clusterWeight;
        dqClusterWeight *= mix(1.0, -1.0, float(dot(real, polarityReference) < 0.0));

        sAccum += scale * clusterWeight;
        rAccum += real * dqClusterWeight;
        dAccum += dual * dqClusterWeight;
        cAccum += cauterizedPos * clusterWeight;
    }

    // normalize dual quaternion
    float norm = length(rAccum);
    rAccum /= norm;
    dAccum /= norm;

    // conversion from dual quaternion to 4x4 matrix.
    mat4 m = dualQuatToMat4(rAccum, dAccum);

    // sAccum.w indicates the amount of cauterization for this vertex.
    // 0 indicates no cauterization and 1 indicates full cauterization.
    // TODO: make this cauterization smoother or implement full dual-quaternion scale support.
    {
        const float CAUTERIZATION_THRESHOLD = 0.1;
        float check = float(sAccum.w > CAUTERIZATION_THRESHOLD);
        sAccum.w = mix(1.0, sAccum.w, check);
        skinnedPosition = mix(m * (sAccum * inPosition), cAccum, check);
    }

 <@if USE_NORMAL@>
    skinnedNormal = vec3(m * vec4(inNormal, 0));
<@endif@>
<@if USE_TANGENT@>
    skinnedTangent = vec3(m * vec4(inTangent, 0));
<@endif@>
}

<@else@>  // NOT USE_DUAL_QUATERNION_SKINNING

// LiNEAR BLENDING
void evalSkinning(ivec4 skinClusterIndex, vec4 skinClusterWeight, vec4 inPosition, out vec4 skinnedPosition
<@if USE_NORMAL@>
    , vec3 inNormal, out vec3 skinnedNormal
<@endif@>
<@if USE_TANGENT@>
    , vec3 inTangent, out vec3 skinnedTangent
<@endif@>
) {
    vec4 newPosition = vec4(0.0, 0.0, 0.0, 0.0);
<@if USE_NORMAL@>
    vec4 newNormal = vec4(0.0, 0.0, 0.0, 0.0);
<@endif@>
<@if USE_TANGENT@>
    vec4 newTangent = vec4(0.0, 0.0, 0.0, 0.0);
<@endif@>

    for (int i = 0; i < INDICES_PER_VERTEX; i++) {
        mat4 clusterMatrix = clusterMatrices[(skinClusterIndex[i])];
        float clusterWeight = skinClusterWeight[i];
        newPosition += clusterMatrix * inPosition * clusterWeight;
<@if USE_NORMAL@>
        newNormal += clusterMatrix * vec4(inNormal.xyz, 0.0) * clusterWeight;
<@endif@>
<@if USE_TANGENT@>
        newTangent += clusterMatrix * vec4(inTangent.xyz, 0.0) * clusterWeight;
<@endif@>
    }

    skinnedPosition = newPosition;
<@if USE_NORMAL@>
    skinnedNormal = newNormal.xyz;
<@endif@>
<@if USE_TANGENT@>
    skinnedTangent = newTangent.xyz;
<@endif@>
}

<@endif@> // if USE_DUAL_QUATERNION_SKINNING

<@endfunc@> // func declareSkinning()

<@endif@> // if not SKINNING_SLH