1 files changed, 78 insertions, 16 deletions
diff --git a/indra/newview/app_settings/shaders/class1/deferred/textureUtilV.glsl b/indra/newview/app_settings/shaders/class1/deferred/textureUtilV.glsl
index 8e641522e3..c75a0e0d5d 100644
--- a/indra/newview/app_settings/shaders/class1/deferred/textureUtilV.glsl
+++ b/indra/newview/app_settings/shaders/class1/deferred/textureUtilV.glsl
@@ -48,6 +48,7 @@ vec2 khr_texture_transform(vec2 texcoord, vec2 scale, float rotation, vec2 offse
     return (transform * vec3(texcoord, 1)).xy;
 }
 
+// A texture transform function for PBR materials applied to shape prims/Collada model prims
 // vertex_texcoord - The UV texture coordinates sampled from the vertex at
 //     runtime. Per SL convention, this is in a right-handed UV coordinate
 //     system. Collada models also have right-handed UVs.
@@ -65,7 +66,7 @@ vec2 texture_transform(vec2 vertex_texcoord, vec4[2] khr_gltf_transform, mat4 sl
     // Apply texture animation first to avoid shearing and other artifacts
     texcoord = (sl_animation_transform * vec4(texcoord, 0, 1)).xy;
     // Convert to left-handed coordinate system. The offset of 1 is necessary
-    // for rotations to be applied correctly.
+    // for rotation and scale to be applied correctly.
     texcoord.y = 1.0 - texcoord.y;
     texcoord = khr_texture_transform(texcoord, khr_gltf_transform[0].xy, khr_gltf_transform[0].z, khr_gltf_transform[1].xy);
     // Convert back to right-handed coordinate system
@@ -77,39 +78,97 @@ vec2 texture_transform(vec2 vertex_texcoord, vec4[2] khr_gltf_transform, mat4 sl
     return texcoord;
 }
 
+// Similar to texture_transform but no offset during coordinate system
+// conversion, and no texture animation support.
+vec2 terrain_texture_transform(vec2 vertex_texcoord, vec4[2] khr_gltf_transform)
+{
+    vec2 texcoord = vertex_texcoord;
+
+    texcoord.y = -texcoord.y;
+    texcoord = khr_texture_transform(texcoord, khr_gltf_transform[0].xy, khr_gltf_transform[0].z, khr_gltf_transform[1].xy);
+    texcoord.y = -texcoord.y;
+
+    return texcoord;
+}
+
 // Take the rotation only from both transforms and apply to the tangent. This
 // accounts for the change of the topology of the normal texture when a texture
 // rotation is applied to it.
+// In practice, this applies the inverse of the texture transform to the tangent.
+// It is effectively an inverse of the rotation
 // *HACK: Assume the imported GLTF model did not have both normal texture
 // transforms and tangent vertices. The use of this function is inconsistent
 // with the GLTF sample viewer when that is the case. See getNormalInfo in
 // https://raw.githubusercontent.com/KhronosGroup/glTF-Sample-Viewer/47a191931461a6f2e14de48d6da0f0eb6ec2d147/source/Renderer/shaders/material_info.glsl
 // We may want to account for this case during GLTF model import.
 // -Cosmic,2023-06-06
-vec3 tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] khr_gltf_transform, mat4 sl_animation_transform)
+vec4 tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] khr_gltf_transform, mat4 sl_animation_transform)
 {
-    vec2 weights = vec2(0, 1);
-
-    // Apply texture animation first to avoid shearing and other artifacts (rotation only)
-    mat2 sl_rot_scale;
-    sl_rot_scale[0][0] = sl_animation_transform[0][0];
-    sl_rot_scale[0][1] = sl_animation_transform[0][1];
-    sl_rot_scale[1][0] = sl_animation_transform[1][0];
-    sl_rot_scale[1][1] = sl_animation_transform[1][1];
-    weights = sl_rot_scale * weights;
-    // Remove scale
+    // Immediately convert to left-handed coordinate system, but it has no
+    // effect here because y is 0 ((1,0) -> (1,0))
+    vec2 weights = vec2(1, 0);
+
+    // Apply inverse KHR_texture_transform (rotation and scale sign 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;
+    vec2 khr_scale_sign = sign(khr_gltf_transform[0].xy);
+    weights *= khr_scale_sign.xy;
+
+    // *NOTE: Delay conversion to right-handed coordinate system here, to
+    // remove the need for computing the inverse of the SL texture animation
+    // matrix.
+
+    // Apply texture animation last to avoid shearing and other artifacts (rotation only)
+    mat2 inv_sl_rot_scale;
+    inv_sl_rot_scale[0][0] = sl_animation_transform[0][0];
+    inv_sl_rot_scale[0][1] = sl_animation_transform[0][1];
+    inv_sl_rot_scale[1][0] = sl_animation_transform[1][0];
+    inv_sl_rot_scale[1][1] = sl_animation_transform[1][1];
+    weights = inv_sl_rot_scale * weights;
+    // *NOTE: Scale to be removed later
+
+    // Set weights to default if 0 for some reason
+    weights.x += 1.0 - abs(sign(sign(weights.x) + (0.5 * sign(weights.y))));
+
+    // Remove scale from SL texture animation transform
     weights = normalize(weights);
 
-    // Convert to left-handed coordinate system
+    // Convert back to right-handed coordinate system
     weights.y = -weights.y;
 
-    // Apply KHR_texture_transform (rotation only)
-    float khr_rotation = khr_gltf_transform[0].z;
+    // 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);
+
+    // An additional sign flip prevents the binormal from being flipped as a
+    // result of a propagation of the tangent sign during the cross product.
+    float sign_flip = khr_scale_sign.x * khr_scale_sign.y;
+    return vec4((weights.x * vertex_tangent.xyz) + (weights.y * vertex_binormal.xyz), vertex_tangent.w * sign_flip);
+}
+
+// Similar to tangent_space_transform but no texture animation support.
+vec4 terrain_tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] khr_gltf_transform)
+{
+    // Immediately convert to left-handed coordinate system, but it has no
+    // effect here because y is 0 ((1,0) -> (1,0))
+    vec2 weights = vec2(1, 0);
+
+    // Apply inverse KHR_texture_transform (rotation and scale sign 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;
+    vec2 khr_scale_sign = sign(khr_gltf_transform[0].xy);
+    weights *= khr_scale_sign.xy;
+
+    // Set weights to default if 0 for some reason
+    weights.x += 1.0 - abs(sign(sign(weights.x) + (0.5 * sign(weights.y))));
 
     // Convert back to right-handed coordinate system
     weights.y = -weights.y;
@@ -118,5 +177,8 @@ vec3 tangent_space_transform(vec4 vertex_tangent, vec3 vertex_normal, vec4[2] kh
     // 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);
+    // An additional sign flip prevents the binormal from being flipped as a
+    // result of a propagation of the tangent sign during the cross product.
+    float sign_flip = khr_scale_sign.x * khr_scale_sign.y;
+    return vec4((weights.x * vertex_tangent.xyz) + (weights.y * vertex_binormal.xyz), vertex_tangent.w * sign_flip);
 }