#1718 Add GLTF support for multiple texcoords (#1720)

* Fix for GLTF MeshPrimitiveModes test

15 files changed, 318 insertions, 84 deletions

diff --git a/indra/llrender/llglslshader.h b/indra/llrender/llglslshader.h
index f2b5c4881c..d42df28809 100644
--- a/indra/llrender/llglslshader.h
+++ b/indra/llrender/llglslshader.h
@@ -328,14 +328,16 @@ public:
     // bit 0 = alpha mode blend (1) or opaque (0)
     // bit 1 = rigged (1) or static (0)
     // bit 2 = unlit (1) or lit (0)
+    // bit 3 = single (0) or multi (1) uv coordinates
     struct GLTFVariant
     {
         constexpr static U8 ALPHA_BLEND = 1;
         constexpr static U8 RIGGED = 2;
         constexpr static U8 UNLIT = 4;
+        constexpr static U8 MULTI_UV = 8;
     };
 
-    constexpr static U8 NUM_GLTF_VARIANTS = 8;
+    constexpr static U8 NUM_GLTF_VARIANTS = 16;
 
     std::vector<LLGLSLShader> mGLTFVariants;
 
diff --git a/indra/llrender/llrender.cpp b/indra/llrender/llrender.cpp
index 51028e5667..cfefde3acc 100644
--- a/indra/llrender/llrender.cpp
+++ b/indra/llrender/llrender.cpp
@@ -1686,7 +1686,7 @@ void LLRender::flush()
 
                 if (attribute_mask & LLVertexBuffer::MAP_TEXCOORD0)
                 {
-                    vb->setTexCoordData(mTexcoordsp.get());
+                    vb->setTexCoord0Data(mTexcoordsp.get());
                 }
 
                 if (attribute_mask & LLVertexBuffer::MAP_COLOR)
diff --git a/indra/llrender/llshadermgr.cpp b/indra/llrender/llshadermgr.cpp
index 5f30fc3879..6f4454f07a 100644
--- a/indra/llrender/llshadermgr.cpp
+++ b/indra/llrender/llshadermgr.cpp
@@ -1180,6 +1180,11 @@ void LLShaderMgr::initAttribsAndUniforms()
     mReservedUniforms.push_back("texture_metallic_roughness_transform"); // (GLTF)
     mReservedUniforms.push_back("texture_occlusion_transform"); // (GLTF)
     mReservedUniforms.push_back("texture_emissive_transform"); // (GLTF)
+    mReservedUniforms.push_back("base_color_texcoord"); // (GLTF)
+    mReservedUniforms.push_back("emissive_texcoord"); // (GLTF)
+    mReservedUniforms.push_back("normal_texcoord"); // (GLTF)
+    mReservedUniforms.push_back("metallic_roughness_texcoord"); // (GLTF)
+    mReservedUniforms.push_back("occlusion_texcoord"); // (GLTF)
 
     mReservedUniforms.push_back("terrain_texture_transforms"); // (GLTF)
 
diff --git a/indra/llrender/llshadermgr.h b/indra/llrender/llshadermgr.h
index 244fc41de6..c00aff3a9a 100644
--- a/indra/llrender/llshadermgr.h
+++ b/indra/llrender/llshadermgr.h
@@ -58,6 +58,11 @@ public:
         TEXTURE_METALLIC_ROUGHNESS_TRANSFORM, //  "texture_metallic_roughness_transform" (GLTF)
         TEXTURE_OCCLUSION_TRANSFORM,          //  "texture_occlusion_transform" (GLTF)
         TEXTURE_EMISSIVE_TRANSFORM,           //  "texture_emissive_transform" (GLTF)
+        BASE_COLOR_TEXCOORD,                  //  "base_color_texcoord" (GLTF)
+        EMISSIVE_TEXCOORD,                    //  "emissive_texcoord" (GLTF)
+        NORMAL_TEXCOORD,                      //  "normal_texcoord" (GLTF)
+        METALLIC_ROUGHNESS_TEXCOORD,          //  "metallic_roughness_texcoord" (GLTF)
+        OCCLUSION_TEXCOORD,                   //  "occlusion_texcoord" (GLTF)
 
         TERRAIN_TEXTURE_TRANSFORMS,           //  "terrain_texture_transforms" (GLTF)
 
diff --git a/indra/llrender/llvertexbuffer.cpp b/indra/llrender/llvertexbuffer.cpp
index a4d33c91df..33f7a6527f 100644
--- a/indra/llrender/llvertexbuffer.cpp
+++ b/indra/llrender/llvertexbuffer.cpp
@@ -1635,7 +1635,7 @@ void LLVertexBuffer::setPositionData(const LLVector4a* data)
     flush_vbo(GL_ARRAY_BUFFER, 0, sizeof(LLVector4a) * getNumVerts()-1, (U8*) data, mMappedData);
 }
 
-void LLVertexBuffer::setTexCoordData(const LLVector2* data)
+void LLVertexBuffer::setTexCoord0Data(const LLVector2* data)
 {
 #if !LL_DARWIN
     llassert(sGLRenderBuffer == mGLBuffer);
@@ -1643,6 +1643,14 @@ void LLVertexBuffer::setTexCoordData(const LLVector2* data)
     flush_vbo(GL_ARRAY_BUFFER, mOffsets[TYPE_TEXCOORD0], mOffsets[TYPE_TEXCOORD0] + sTypeSize[TYPE_TEXCOORD0] * getNumVerts() - 1, (U8*)data, mMappedData);
 }
 
+void LLVertexBuffer::setTexCoord1Data(const LLVector2* data)
+{
+#if !LL_DARWIN
+    llassert(sGLRenderBuffer == mGLBuffer);
+#endif
+    flush_vbo(GL_ARRAY_BUFFER, mOffsets[TYPE_TEXCOORD1], mOffsets[TYPE_TEXCOORD1] + sTypeSize[TYPE_TEXCOORD1] * getNumVerts() - 1, (U8*)data, mMappedData);
+}
+
 void LLVertexBuffer::setColorData(const LLColor4U* data)
 {
 #if !LL_DARWIN
diff --git a/indra/llrender/llvertexbuffer.h b/indra/llrender/llvertexbuffer.h
index 94339191a4..66a7f2bf26 100644
--- a/indra/llrender/llvertexbuffer.h
+++ b/indra/llrender/llvertexbuffer.h
@@ -196,7 +196,8 @@ public:
     void setTangentData(const LLVector4a* data);
     void setWeight4Data(const LLVector4a* data);
     void setJointData(const U64* data);
-    void setTexCoordData(const LLVector2* data);
+    void setTexCoord0Data(const LLVector2* data);
+    void setTexCoord1Data(const LLVector2* data);
     void setColorData(const LLColor4U* data);
     void setIndexData(const U16* data);
     void setIndexData(const U32* data);
diff --git a/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessF.glsl b/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessF.glsl
index 99bfcf70fa..789c00259b 100644
--- a/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessF.glsl
+++ b/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessF.glsl
@@ -37,8 +37,8 @@ uniform sampler2D emissiveMap;
 uniform vec3 emissiveColor;
 in vec3 vary_position;
 in vec4 vertex_color;
-in vec2 base_color_texcoord;
-in vec2 emissive_texcoord;
+in vec2 base_color_uv;
+in vec2 emissive_uv;
 uniform float minimum_alpha;
 
 void mirrorClip(vec3 pos);
@@ -59,9 +59,9 @@ uniform float roughnessFactor;
 in vec3 vary_normal;
 in vec3 vary_tangent;
 flat in float vary_sign;
-in vec2 normal_texcoord;
-in vec2 metallic_roughness_texcoord;
-in vec2 occlusion_texcoord;
+in vec2 normal_uv;
+in vec2 metallic_roughness_uv;
+in vec2 occlusion_uv;
 #endif
 // ==================================
 
@@ -165,7 +165,7 @@ void main()
     vec3 pos = vary_position;
     mirrorClip(pos);
 
-    vec4 basecolor = texture(diffuseMap, base_color_texcoord.xy).rgba;
+    vec4 basecolor = texture(diffuseMap, base_color_uv.xy).rgba;
     basecolor.rgb = srgb_to_linear(basecolor.rgb);
     basecolor *= vertex_color;
 
@@ -175,7 +175,7 @@ void main()
     }
 
     vec3 emissive = emissiveColor;
-    emissive *= srgb_to_linear(texture(emissiveMap, emissive_texcoord.xy).rgb);
+    emissive *= srgb_to_linear(texture(emissiveMap, emissive_uv.xy).rgb);
 // ==================================
 
 // ==================================
@@ -185,7 +185,7 @@ void main()
 // ==================================
 #ifndef UNLIT
     // from mikktspace.com
-    vec3 vNt = texture(normalMap, normal_texcoord.xy).xyz*2.0-1.0;
+    vec3 vNt = texture(normalMap, normal_uv.xy).xyz*2.0-1.0;
     float sign = vary_sign;
     vec3 vN = vary_normal;
     vec3 vT = vary_tangent.xyz;
@@ -199,8 +199,8 @@ void main()
     //   occlusion 1.0
     //   roughness 0.0
     //   metal     0.0
-    vec3 orm = texture(metallicRoughnessMap, metallic_roughness_texcoord.xy).rgb;
-    orm.r = texture(occlusionMap, occlusion_texcoord.xy).r;
+    vec3 orm = texture(metallicRoughnessMap, metallic_roughness_uv.xy).rgb;
+    orm.r = texture(occlusionMap, occlusion_uv.xy).r;
     orm.g *= roughnessFactor;
     orm.b *= metallicFactor;
 #endif
diff --git a/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessV.glsl b/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessV.glsl
index bc9a47d41e..aac3dc917f 100644
--- a/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessV.glsl
+++ b/indra/newview/app_settings/shaders/class1/gltf/pbrmetallicroughnessV.glsl
@@ -33,7 +33,6 @@ uniform mat4 projection_matrix;
 uniform mat3 normal_matrix;
 uniform mat4 modelview_projection_matrix;
 #endif
-uniform mat4 texture_matrix0;
 
 uniform vec4[2] texture_base_color_transform;
 uniform vec4[2] texture_normal_transform;
@@ -44,21 +43,31 @@ uniform vec4[2] texture_occlusion_transform;
 in vec3 position;
 in vec4 diffuse_color;
 in vec2 texcoord0;
-out vec2 base_color_texcoord;
-out vec2 emissive_texcoord;
+out vec2 base_color_uv;
+out vec2 emissive_uv;
 out vec4 vertex_color;
 out vec3 vary_position;
 
 #ifndef UNLIT
 in vec3 normal;
 in vec4 tangent;
-out vec2 normal_texcoord;
-out vec2 metallic_roughness_texcoord;
-out vec2 occlusion_texcoord;
+out vec2 normal_uv;
+out vec2 metallic_roughness_uv;
+out vec2 occlusion_uv;
 out vec3 vary_tangent;
 flat out float vary_sign;
 out vec3 vary_normal;
-vec3 tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] khr_gltf_transform, mat4 sl_animation_transform);
+#endif
+
+#ifdef MULTI_UV
+in vec2 texcoord1;
+uniform int base_color_texcoord;
+uniform int emissive_texcoord;
+#ifndef UNLIT
+uniform int normal_texcoord;
+uniform int metallic_roughness_texcoord;
+uniform int occlusion_texcoord;
+#endif
 #endif
 
 vec2 gltf_texture_transform(vec2 texcoord, vec4[2] p)
@@ -86,6 +95,36 @@ vec2 gltf_texture_transform(vec2 texcoord, vec4[2] p)
     return uvTransformed;
 }
 
+#ifndef UNLIT
+vec3 gltf_tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] khr_gltf_transform)
+{ //derived from tangent_space_transform in textureUtilV.glsl
+    vec2 weights = vec2(0, 1);
+
+    // Convert to left-handed coordinate system
+    weights.y = -weights.y;
+
+    // Apply KHR_texture_transform (rotation only)
+    float khr_rotation = khr_gltf_transform[0].z;
+    mat2 khr_rotation_mat = mat2(
+        cos(khr_rotation),-sin(khr_rotation),
+        sin(khr_rotation), cos(khr_rotation)
+    );
+    weights = khr_rotation_mat * weights;
+
+    // Convert back to right-handed coordinate system
+    weights.y = -weights.y;
+
+    // Similar to the MikkTSpace-compatible method of extracting the binormal
+    // from the normal and tangent, as seen in the fragment shader
+    vec3 vertex_binormal = vertex_tangent.w * cross(vertex_normal, vertex_tangent.xyz);
+
+    return (weights.x * vertex_binormal.xyz) + (weights.y * vertex_tangent.xyz);
+
+    return vertex_tangent.xyz;
+}
+#endif
+
+
 
 #ifdef ALPHA_BLEND
 out vec3 vary_fragcoord;
@@ -161,13 +200,40 @@ void main()
     gl_Position = vert;
 #endif
 
-    base_color_texcoord = gltf_texture_transform(texcoord0, texture_base_color_transform);
-    emissive_texcoord = gltf_texture_transform(texcoord0, texture_emissive_transform);
+    vec2 bcuv;
+    vec2 emuv;
+
+#ifdef MULTI_UV
+    vec2 uv[2];
+    uv[0] = texcoord0;
+    uv[1] = texcoord1;
+
+    bcuv = uv[base_color_texcoord];
+    emuv = uv[emissive_texcoord];
+#else
+    bcuv = texcoord0;
+    emuv = texcoord0;
+#endif
+
+    base_color_uv = gltf_texture_transform(bcuv, texture_base_color_transform);
+    emissive_uv = gltf_texture_transform(emuv, texture_emissive_transform);
 
 #ifndef UNLIT
-    normal_texcoord = gltf_texture_transform(texcoord0, texture_normal_transform);
-    metallic_roughness_texcoord = gltf_texture_transform(texcoord0, texture_metallic_roughness_transform);
-    occlusion_texcoord = gltf_texture_transform(texcoord0, texture_occlusion_transform);
+    vec2 normuv;
+    vec2 rmuv;
+    vec2 ouv;
+#ifdef MULTI_UV
+    normuv = uv[normal_texcoord];
+    rmuv = uv[metallic_roughness_texcoord];
+    ouv = uv[occlusion_texcoord];
+#else
+    normuv = texcoord0;
+    rmuv = texcoord0;
+    ouv = texcoord0;
+#endif
+    normal_uv = gltf_texture_transform(normuv, texture_normal_transform);
+    metallic_roughness_uv = gltf_texture_transform(rmuv, texture_metallic_roughness_transform);
+    occlusion_uv = gltf_texture_transform(ouv, texture_occlusion_transform);
 #endif
 
 #ifndef UNLIT
@@ -180,7 +246,7 @@ void main()
 #endif
 
     n = normalize(n);
-    vary_tangent = normalize(tangent_space_transform(vec4(t, tangent.w), n, texture_normal_transform, texture_matrix0));
+    vary_tangent = normalize(gltf_tangent_space_transform(vec4(t, tangent.w), n, texture_normal_transform));
     vary_sign = tangent.w;
     vary_normal = n;
 #endif
diff --git a/indra/newview/gltf/asset.cpp b/indra/newview/gltf/asset.cpp
index 4c1da3e645..21be69aae2 100644
--- a/indra/newview/gltf/asset.cpp
+++ b/indra/newview/gltf/asset.cpp
@@ -910,6 +910,24 @@ void Material::TextureInfo::serialize(object& dst) const
     write_extensions(dst, &mTextureTransform, "KHR_texture_transform");
 }
 
+S32 Material::TextureInfo::getTexCoord() const
+{
+    if (mTextureTransform.mPresent && mTextureTransform.mTexCoord != INVALID_INDEX)
+    {
+        return mTextureTransform.mTexCoord;
+    }
+    return mTexCoord;
+}
+
+bool Material::isMultiUV() const
+{
+    return mPbrMetallicRoughness.mBaseColorTexture.getTexCoord() != 0 ||
+        mPbrMetallicRoughness.mMetallicRoughnessTexture.getTexCoord() != 0 ||
+        mNormalTexture.getTexCoord() != 0 ||
+        mOcclusionTexture.getTexCoord() != 0 ||
+        mEmissiveTexture.getTexCoord() != 0;
+}
+
 const Material::TextureInfo& Material::TextureInfo::operator=(const Value& src)
 {
     if (src.is_object())
@@ -1048,7 +1066,7 @@ void TextureTransform::serialize(object& dst) const
     write(mOffset, "offset", dst, vec2(0.f, 0.f));
     write(mRotation, "rotation", dst, 0.f);
     write(mScale, "scale", dst, vec2(1.f, 1.f));
-    write(mTexCoord, "texCoord", dst, 0);
+    write(mTexCoord, "texCoord", dst, -1);
 }
 
 
diff --git a/indra/newview/gltf/asset.h b/indra/newview/gltf/asset.h
index bca269d5dc..ea3f7d480a 100644
--- a/indra/newview/gltf/asset.h
+++ b/indra/newview/gltf/asset.h
@@ -102,6 +102,10 @@ namespace LL
                 bool operator==(const TextureInfo& rhs) const;
                 bool operator!=(const TextureInfo& rhs) const;
 
+                // get the UV channel that should be used for sampling this texture
+                // returns mTextureTransform.mTexCoord if present and valid, otherwise mTexCoord
+                S32 getTexCoord() const;
+
                 const TextureInfo& operator=(const Value& src);
                 void serialize(boost::json::object& dst) const;
             };
@@ -152,6 +156,8 @@ namespace LL
             bool mDoubleSided = false;
             Unlit mUnlit;
 
+            bool isMultiUV() const;
+
             const Material& operator=(const Value& src);
             void serialize(boost::json::object& dst) const;
         };
diff --git a/indra/newview/gltf/buffer_util.h b/indra/newview/gltf/buffer_util.h
index 943a1748f9..c1101818b7 100644
--- a/indra/newview/gltf/buffer_util.h
+++ b/indra/newview/gltf/buffer_util.h
@@ -826,7 +826,7 @@ namespace LL
                 if (arr.size() == 2)
                 {
                     std::error_code ec;
-                    vec3 t;
+                    vec2 t;
                     t.x = arr[0].to_number<F32>(ec); if (ec) return false;
                     t.y = arr[1].to_number<F32>(ec); if (ec) return false;
 
diff --git a/indra/newview/gltf/primitive.cpp b/indra/newview/gltf/primitive.cpp
index bc333aff69..4cff0622b3 100644
--- a/indra/newview/gltf/primitive.cpp
+++ b/indra/newview/gltf/primitive.cpp
@@ -42,13 +42,14 @@ using namespace boost::json;
 // Mesh data useful for Mikktspace tangent generation (and flat normal generation)
 struct MikktMesh
 {
-    std::vector<LLVector3> p;
-    std::vector<LLVector3> n;
-    std::vector<LLVector2> tc;
-    std::vector<LLVector4> w;
-    std::vector<LLVector4> t;
-    std::vector<LLColor4U> c;
-    std::vector<U64> j;
+    std::vector<LLVector3> p;       //positions
+    std::vector<LLVector3> n;       //normals
+    std::vector<LLVector4> t;       //tangents
+    std::vector<LLVector2> tc0;     //texcoords 0
+    std::vector<LLVector2> tc1;     //texcoords 1
+    std::vector<LLColor4U> c;       //colors
+    std::vector<LLVector4> w;       //weights
+    std::vector<U64> j;             //joints
 
     // initialize from src primitive and make an unrolled triangle list
     // returns false if the Primitive cannot be converted to a triangle list
@@ -57,15 +58,28 @@ struct MikktMesh
         bool indexed = !prim->mIndexArray.empty();
         U32 vert_count = indexed ? prim->mIndexArray.size() : prim->mPositions.size();
 
-        if (prim->mMode != Primitive::Mode::TRIANGLES)
+        U32 triangle_count = 0;
+
+        if (prim->mMode == Primitive::Mode::TRIANGLE_STRIP ||
+            prim->mMode == Primitive::Mode::TRIANGLE_FAN)
+        {
+            triangle_count = vert_count - 2;
+        }
+        else if (prim->mMode == Primitive::Mode::TRIANGLES)
         {
-            LL_WARNS("GLTF") << "Unsupported primitive mode for conversion to triangles: " << (S32) prim->mMode << LL_ENDL;
+            triangle_count = vert_count / 3;
+        }
+        else
+        {
+            LL_WARNS("GLTF") << "Unsupported primitive mode for conversion to triangles: " << (S32)prim->mMode << LL_ENDL;
             return false;
         }
 
+        vert_count = triangle_count * 3;
+
         p.resize(vert_count);
         n.resize(vert_count);
-        tc.resize(vert_count);
+        tc0.resize(vert_count);
         c.resize(vert_count);
 
         bool has_normals = !prim->mNormals.empty();
@@ -78,6 +92,7 @@ struct MikktMesh
         {
             t.resize(vert_count);
         }
+
         bool rigged = !prim->mWeights.empty();
         if (rigged)
         {
@@ -85,23 +100,69 @@ struct MikktMesh
             j.resize(vert_count);
         }
 
-        for (int i = 0; i < vert_count; ++i)
+        bool multi_uv = !prim->mTexCoords1.empty();
+        if (multi_uv)
         {
-            U32 idx = indexed ? prim->mIndexArray[i] : i;
+            tc1.resize(vert_count);
+        }
 
-            p[i].set(prim->mPositions[idx].getF32ptr());
-            tc[i].set(prim->mTexCoords[idx]);
-            c[i] = prim->mColors[idx];
+        for (int tri_idx = 0; tri_idx < triangle_count; ++tri_idx)
+        {
+            U32 idx[3];
+
+            if (prim->mMode == Primitive::Mode::TRIANGLES)
+            {
+                idx[0] = tri_idx * 3;
+                idx[1] = tri_idx * 3 + 1;
+                idx[2] = tri_idx * 3 + 2;
+            }
+            else if (prim->mMode == Primitive::Mode::TRIANGLE_STRIP)
+            {
+                idx[0] = tri_idx;
+                idx[1] = tri_idx + 1;
+                idx[2] = tri_idx + 2;
 
-            if (has_normals)
+                if (tri_idx % 2 != 0)
+                {
+                    std::swap(idx[1], idx[2]);
+                }
+            }
+            else if (prim->mMode == Primitive::Mode::TRIANGLE_FAN)
             {
-                n[i].set(prim->mNormals[idx].getF32ptr());
+                idx[0] = 0;
+                idx[1] = tri_idx + 1;
+                idx[2] = tri_idx + 2;
             }
 
-            if (rigged)
+            if (indexed)
             {
-                w[i].set(prim->mWeights[idx].getF32ptr());
-                j[i] = prim->mJoints[idx];
+                idx[0] = prim->mIndexArray[idx[0]];
+                idx[1] = prim->mIndexArray[idx[1]];
+                idx[2] = prim->mIndexArray[idx[2]];
+            }
+
+            for (U32 v = 0; v < 3; ++v)
+            {
+                U32 i = tri_idx * 3 + v;
+                p[i].set(prim->mPositions[idx[v]].getF32ptr());
+                tc0[i].set(prim->mTexCoords0[idx[v]]);
+                c[i] = prim->mColors[idx[v]];
+
+                if (multi_uv)
+                {
+                    tc1[i].set(prim->mTexCoords1[idx[v]]);
+                }
+
+                if (has_normals)
+                {
+                    n[i].set(prim->mNormals[idx[v]].getF32ptr());
+                }
+
+                if (rigged)
+                {
+                    w[i].set(prim->mWeights[idx[v]].getF32ptr());
+                    j[i] = prim->mJoints[idx[v]];
+                }
             }
         }
 
@@ -138,25 +199,34 @@ struct MikktMesh
     void write(Primitive* prim) const
     {
         //re-weld
-        meshopt_Stream mos[] =
+        std::vector<meshopt_Stream> mos =
         {
             { &p[0], sizeof(LLVector3), sizeof(LLVector3) },
             { &n[0], sizeof(LLVector3), sizeof(LLVector3) },
             { &t[0], sizeof(LLVector4), sizeof(LLVector4) },
-            { &tc[0], sizeof(LLVector2), sizeof(LLVector2) },
-            { &c[0], sizeof(LLColor4U), sizeof(LLColor4U) },
-            { w.empty() ? nullptr : &w[0], sizeof(LLVector4), sizeof(LLVector4) },
-            { j.empty() ? nullptr : &j[0], sizeof(U64), sizeof(U64) }
+            { &tc0[0], sizeof(LLVector2), sizeof(LLVector2) },
+            { &c[0], sizeof(LLColor4U), sizeof(LLColor4U) }
         };
 
+        if (!w.empty())
+        {
+            mos.push_back({ &w[0], sizeof(LLVector4), sizeof(LLVector4) });
+            mos.push_back({ &j[0], sizeof(U64), sizeof(U64) });
+        }
+
+        if (!tc1.empty())
+        {
+            mos.push_back({ &tc1[0], sizeof(LLVector2), sizeof(LLVector2) });
+        }
+
         std::vector<U32> remap;
         remap.resize(p.size());
 
-        U32 stream_count = w.empty() ? 5 : 7;
+        U32 stream_count = mos.size();
 
-        size_t vert_count = meshopt_generateVertexRemapMulti(&remap[0], nullptr, p.size(), p.size(), mos, stream_count);
+        size_t vert_count = meshopt_generateVertexRemapMulti(&remap[0], nullptr, p.size(), p.size(), mos.data(), stream_count);
 
-        prim->mTexCoords.resize(vert_count);
+        prim->mTexCoords0.resize(vert_count);
         prim->mNormals.resize(vert_count);
         prim->mTangents.resize(vert_count);
         prim->mPositions.resize(vert_count);
@@ -166,6 +236,10 @@ struct MikktMesh
             prim->mWeights.resize(vert_count);
             prim->mJoints.resize(vert_count);
         }
+        if (!tc1.empty())
+                    {
+            prim->mTexCoords1.resize(vert_count);
+        }
         
         prim->mIndexArray.resize(remap.size());
 
@@ -178,7 +252,7 @@ struct MikktMesh
 
             prim->mPositions[dst_idx].load3(p[src_idx].mV);
             prim->mNormals[dst_idx].load3(n[src_idx].mV);
-            prim->mTexCoords[dst_idx] = tc[src_idx];
+            prim->mTexCoords0[dst_idx] = tc0[src_idx];
             prim->mTangents[dst_idx].loadua(t[src_idx].mV);
             prim->mColors[dst_idx] = c[src_idx];
 
@@ -187,6 +261,11 @@ struct MikktMesh
                 prim->mWeights[dst_idx].loadua(w[src_idx].mV);
                 prim->mJoints[dst_idx] = j[src_idx];
             }
+
+            if (!tc1.empty())
+            {
+                prim->mTexCoords1[dst_idx] = tc1[src_idx];
+            }
         }
 
         prim->mGLMode = LLRender::TRIANGLES;
@@ -210,8 +289,8 @@ struct MikktMesh
 
     mikk::float3 GetTexCoord(const uint32_t face_num, const uint32_t vert_num)
     {
-        F32* uv = tc[face_num * 3 + vert_num].mV;
-        return mikk::float3(uv[0], uv[1], 1.0f);
+        F32* uv = tc0[face_num * 3 + vert_num].mV;
+        return mikk::float3(uv[0], 1.f-uv[1], 1.0f);
     }
 
     mikk::float3 GetNormal(const uint32_t face_num, const uint32_t vert_num)
@@ -228,6 +307,14 @@ struct MikktMesh
 };
 
 
+static void vertical_flip(std::vector<LLVector2>& texcoords)
+{
+    for (auto& tc : texcoords)
+    {
+        tc[1] = 1.f - tc[1];
+    }
+}
+
 bool Primitive::prep(Asset& asset)
 {
     // allocate vertex buffer
@@ -261,7 +348,11 @@ bool Primitive::prep(Asset& asset)
         }
         else if (attribName == "TEXCOORD_0")
         {
-            copy(asset, accessor, mTexCoords);
+            copy(asset, accessor, mTexCoords0);
+        }
+        else if (attribName == "TEXCOORD_1")
+        {
+            copy(asset, accessor, mTexCoords1);
         }
         else if (attribName == "JOINTS_0")
         {
@@ -297,24 +388,28 @@ bool Primitive::prep(Asset& asset)
         mask |= LLVertexBuffer::MAP_JOINT;
     }
 
-    if (mTexCoords.empty())
+    if (mTexCoords0.empty())
     {
-        mTexCoords.resize(mPositions.size());
+        mTexCoords0.resize(mPositions.size());
     }
 
-    // TODO: support more than one texcoord set (or no texcoords)
     mask |= LLVertexBuffer::MAP_TEXCOORD0;
 
+    if (!mTexCoords1.empty())
+    {
+        mask |= LLVertexBuffer::MAP_TEXCOORD1;
+    }
+
     if (mColors.empty())
     {
         mColors.resize(mPositions.size(), LLColor4U::white);
     }
 
+    mShaderVariant = 0;
+
     // TODO: support colorless vertex buffers
     mask |= LLVertexBuffer::MAP_COLOR;
 
-    mShaderVariant = 0;
-
     bool unlit = false;
 
     // bake material basecolor into color array
@@ -332,6 +427,11 @@ bool Primitive::prep(Asset& asset)
             mShaderVariant |= LLGLSLShader::GLTFVariant::UNLIT;
             unlit = true;
         }
+
+        if (material.isMultiUV())
+        {
+            mShaderVariant |= LLGLSLShader::GLTFVariant::MULTI_UV;
+        }
     }
 
     if (mNormals.empty() && !unlit)
@@ -434,15 +534,17 @@ bool Primitive::prep(Asset& asset)
     }
 
     // flip texcoord y, upload, then flip back (keep the off-spec data in vram only)
-    for (auto& tc : mTexCoords)
-    {
-        tc[1] = 1.f - tc[1];
-    }
-    mVertexBuffer->setTexCoordData(mTexCoords.data());
-    for (auto& tc : mTexCoords)
+    vertical_flip(mTexCoords0);
+    mVertexBuffer->setTexCoord0Data(mTexCoords0.data());
+    vertical_flip(mTexCoords0);
+
+    if (!mTexCoords1.empty())
     {
-        tc[1] = 1.f - tc[1];
+        vertical_flip(mTexCoords1);
+        mVertexBuffer->setTexCoord1Data(mTexCoords1.data());
+        vertical_flip(mTexCoords1);
     }
+    
 
     if (!mIndexArray.empty())
     {
@@ -453,10 +555,13 @@ bool Primitive::prep(Asset& asset)
 
     mVertexBuffer->unbind();
 
-    Material& material = asset.mMaterials[mMaterial];
-    if (material.mAlphaMode == Material::AlphaMode::BLEND)
+    if (mMaterial != INVALID_INDEX)
     {
-        mShaderVariant |= LLGLSLShader::GLTFVariant::ALPHA_BLEND;
+        Material& material = asset.mMaterials[mMaterial];
+        if (material.mAlphaMode == Material::AlphaMode::BLEND)
+        {
+            mShaderVariant |= LLGLSLShader::GLTFVariant::ALPHA_BLEND;
+        }
     }
 
     return true;
@@ -614,7 +719,7 @@ const LLVolumeTriangle* Primitive::lineSegmentIntersect(const LLVector4a& start,
     //create a proxy LLVolumeFace for the raycast
     LLVolumeFace face;
     face.mPositions = mPositions.data();
-    face.mTexCoords = mTexCoords.data();
+    face.mTexCoords = mTexCoords0.data();
     face.mNormals = mNormals.data();
     face.mTangents = mTangents.data();
     face.mIndices = nullptr; // unreferenced
diff --git a/indra/newview/gltf/primitive.h b/indra/newview/gltf/primitive.h
index f9d7c63c65..7cc05cf831 100644
--- a/indra/newview/gltf/primitive.h
+++ b/indra/newview/gltf/primitive.h
@@ -58,7 +58,8 @@ namespace LL
             LLPointer<LLVertexBuffer> mVertexBuffer;
 
             // CPU copy of mesh data, keep these as LLVector types for compatibility with raycasting code
-            std::vector<LLVector2> mTexCoords;
+            std::vector<LLVector2> mTexCoords0;
+            std::vector<LLVector2> mTexCoords1;
             std::vector<LLVector4a> mNormals;
             std::vector<LLVector4a> mTangents;
             std::vector<LLVector4a> mPositions;
diff --git a/indra/newview/gltfscenemanager.cpp b/indra/newview/gltfscenemanager.cpp
index b390afee37..16f362b3e4 100644
--- a/indra/newview/gltfscenemanager.cpp
+++ b/indra/newview/gltfscenemanager.cpp
@@ -549,10 +549,16 @@ void GLTFSceneManager::render(bool opaque, bool rigged, bool unlit)
 
 void GLTFSceneManager::render(U8 variant)
 {
-    // for debugging, just render the whole scene as opaque
-    // by traversing the whole scenegraph
-    // Assumes camera transform is already set and
-    // appropriate shader is already boundd
+    // just render the whole scene by traversing the whole scenegraph
+    // Assumes camera transform is already set and appropriate shader is already bound.
+    // Eventually we'll want a smarter render pipe that has pre-sorted the scene graph
+    // into buckets by material and shader.
+
+    // HACK -- implicitly render multi-uv variant
+    if (!(variant & LLGLSLShader::GLTFVariant::MULTI_UV))
+    {
+        render((U8) (variant | LLGLSLShader::GLTFVariant::MULTI_UV));
+    }
 
     gGL.matrixMode(LLRender::MM_MODELVIEW);
 
@@ -732,6 +738,7 @@ void GLTFSceneManager::bind(Asset& asset, Material& material)
     F32 tf[8];
     material.mPbrMetallicRoughness.mBaseColorTexture.mTextureTransform.getPacked(tf);
     shader->uniform4fv(LLShaderMgr::TEXTURE_BASE_COLOR_TRANSFORM, 2, tf);
+    shader->uniform1i(LLShaderMgr::BASE_COLOR_TEXCOORD, material.mPbrMetallicRoughness.mBaseColorTexture.getTexCoord());
 
     if (!LLPipeline::sShadowRender)
     {
@@ -748,15 +755,19 @@ void GLTFSceneManager::bind(Asset& asset, Material& material)
 
         material.mNormalTexture.mTextureTransform.getPacked(tf);
         shader->uniform4fv(LLShaderMgr::TEXTURE_NORMAL_TRANSFORM, 2, tf);
+        shader->uniform1i(LLShaderMgr::NORMAL_TEXCOORD, material.mNormalTexture.getTexCoord());
 
         material.mPbrMetallicRoughness.mMetallicRoughnessTexture.mTextureTransform.getPacked(tf);
         shader->uniform4fv(LLShaderMgr::TEXTURE_METALLIC_ROUGHNESS_TRANSFORM, 2, tf);
+        shader->uniform1i(LLShaderMgr::METALLIC_ROUGHNESS_TEXCOORD, material.mPbrMetallicRoughness.mMetallicRoughnessTexture.getTexCoord());
 
         material.mOcclusionTexture.mTextureTransform.getPacked(tf);
         shader->uniform4fv(LLShaderMgr::TEXTURE_OCCLUSION_TRANSFORM, 2, tf);
+        shader->uniform1i(LLShaderMgr::OCCLUSION_TEXCOORD, material.mOcclusionTexture.getTexCoord());
 
         material.mEmissiveTexture.mTextureTransform.getPacked(tf);
         shader->uniform4fv(LLShaderMgr::TEXTURE_EMISSIVE_TRANSFORM, 2, tf);
+        shader->uniform1i(LLShaderMgr::EMISSIVE_TEXCOORD, material.mEmissiveTexture.getTexCoord());
     }
 }
 
diff --git a/indra/newview/llviewershadermgr.cpp b/indra/newview/llviewershadermgr.cpp
index d43d6fea37..5913e7ba6f 100644
--- a/indra/newview/llviewershadermgr.cpp
+++ b/indra/newview/llviewershadermgr.cpp
@@ -249,7 +249,7 @@ static bool make_rigged_variant(LLGLSLShader& shader, LLGLSLShader& riggedShader
 }
 
 
-static bool make_gltf_variant(LLGLSLShader& shader, LLGLSLShader& variant, bool alpha_blend, bool rigged, bool unlit, bool use_sun_shadow)
+static bool make_gltf_variant(LLGLSLShader& shader, LLGLSLShader& variant, bool alpha_blend, bool rigged, bool unlit, bool multi_uv, bool use_sun_shadow)
 {
     variant.mName = shader.mName.c_str();
     variant.mFeatures = shader.mFeatures;
@@ -271,6 +271,11 @@ static bool make_gltf_variant(LLGLSLShader& shader, LLGLSLShader& variant, bool
         variant.addPermutation("UNLIT", "1");
     }
 
+    if (multi_uv)
+    {
+        variant.addPermutation("MULTI_UV", "1");
+    }
+
     if (alpha_blend)
     {
         variant.addPermutation("ALPHA_BLEND", "1");
@@ -317,8 +322,9 @@ static bool make_gltf_variants(LLGLSLShader& shader, bool use_sun_shadow)
         bool alpha_blend = i & LLGLSLShader::GLTFVariant::ALPHA_BLEND;
         bool rigged = i & LLGLSLShader::GLTFVariant::RIGGED;
         bool unlit = i & LLGLSLShader::GLTFVariant::UNLIT;
+        bool multi_uv = i & LLGLSLShader::GLTFVariant::MULTI_UV;
 
-        if (!make_gltf_variant(shader, shader.mGLTFVariants[i], alpha_blend, rigged, unlit, use_sun_shadow))
+        if (!make_gltf_variant(shader, shader.mGLTFVariants[i], alpha_blend, rigged, unlit, multi_uv, use_sun_shadow))
         {
             return false;
         }