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glTF Loader: Use proper basis change for transforms

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Backport the localmesh fixes. 
Upstream glTF has some TODOs. these were fixed in LocalMesh (sawtooth arm bug)
This commit is contained in:
Beq
2026-04-01 17:38:53 +01:00
parent 56aff7efc8
commit bddb3dcc07
1 changed files with 65 additions and 16 deletions
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indra/newview/gltf/llgltfloader.cpp
+65 -16
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@@ -87,6 +87,25 @@ static const glm::mat4 coord_system_rotationxy(
0.f, 0.f, 0.f, 1.f
);
// <FS:Beq> Use a full basis change for transform matrices. Pre-multiplying is
// correct for point positions but not for joint rest/bind matrices.
static glm::mat4 build_viewer_basis_transform(bool apply_xy_rotation)
{
glm::mat4 basis = coord_system_rotation;
if (apply_xy_rotation)
{
basis = coord_system_rotationxy * basis;
}
return basis;
}
static glm::mat4 convert_transform_to_viewer_basis(const glm::mat4& transform, bool apply_xy_rotation)
{
const glm::mat4 basis = build_viewer_basis_transform(apply_xy_rotation);
return basis * transform * glm::inverse(basis);
}
// </FS:Beq>
static const S32 VERTEX_SPLIT_SAFETY_MARGIN = 3 * 3 + 1; // 10 vertices: 3 complete triangles plus remapping overhead
static const S32 VERTEX_LIMIT = USHRT_MAX - VERTEX_SPLIT_SAFETY_MARGIN;
@@ -1372,7 +1391,12 @@ void LLGLTFLoader::populateJointsFromSkin(S32 skin_idx)
{
// Transalte existing bind matrix to viewer's overriden skeleton
glm::mat4 original_bind_matrix = glm::inverse(skin.mInverseBindMatricesData[i]);
glm::mat4 rotated_original = coord_system_rotation * original_bind_matrix;
// <FS:Beq> Transform matrices need a basis change, not a simple
// left multiply, otherwise non-T-pose rigs can pick up a 90 degree
// axis error in the converted bind state.
// glm::mat4 rotated_original = coord_system_rotation * original_bind_matrix;
glm::mat4 rotated_original = convert_transform_to_viewer_basis(original_bind_matrix, mApplyXYRotation);
// </FS:Beq>
glm::mat4 skeleton_transform = computeGltfToViewerSkeletonTransform(joints_data, joint, legal_name);
glm::mat4 tranlated_original = skeleton_transform * rotated_original;
glm::mat4 final_inverse_bind_matrix = glm::inverse(tranlated_original);
@@ -1463,11 +1487,15 @@ void LLGLTFLoader::buildOverrideMatrix(LLJointData& viewer_data, joints_data_map
node.mIsOverrideValid = true;
node.mViewerRestMatrix = viewer_data.mRestMatrix;
glm::mat4 gltf_joint_rest_pose = coord_system_rotation * node.mGltfRestMatrix;
if (mApplyXYRotation)
{
gltf_joint_rest_pose = coord_system_rotationxy * gltf_joint_rest_pose;
}
// <FS:Beq> Convert joint rest matrices with a full basis change so the
// bind/rest chain stays in a consistent viewer-space frame.
// glm::mat4 gltf_joint_rest_pose = coord_system_rotation * node.mGltfRestMatrix;
// if (mApplyXYRotation)
// {
// gltf_joint_rest_pose = coord_system_rotationxy * gltf_joint_rest_pose;
// }
glm::mat4 gltf_joint_rest_pose = convert_transform_to_viewer_basis(node.mGltfRestMatrix, mApplyXYRotation);
// </FS:Beq>
glm::mat4 translated_joint;
// Example:
@@ -1495,14 +1523,20 @@ void LLGLTFLoader::buildOverrideMatrix(LLJointData& viewer_data, joints_data_map
// fortunately normal bones use only translation, without rotation or scale
node.mOverrideMatrix = glm::recompose(glm::vec3(1, 1, 1), glm::identity<glm::quat>(), translation_override, glm::vec3(0, 0, 0), glm::vec4(0, 0, 0, 1));
glm::mat4 overriden_joint = node.mOverrideMatrix;
// todo: if gltf bone had rotation or scale, they probably should be saved here
// then applied to bind matrix
rest = parent_rest * overriden_joint;
// <FS:Beq> Keep the full local TRS for bind/rest propagation.
// glm::mat4 overriden_joint = node.mOverrideMatrix;
// // todo: if gltf bone had rotation or scale, they probably should be saved here
// // then applied to bind matrix
// rest = parent_rest * overriden_joint;
// </FS:Beq>
if (viewer_data.mIsJoint)
{
// <FS:Beq> Keep the full local TRS for bind/rest propagation.
// Using the translation-only override here re-encodes parent
// rotation into child translations and causes the sawtooth arm bug.
rest = parent_rest * translated_joint;
node.mOverrideRestMatrix = rest;
// </FS:Beq>
}
else
{
@@ -1512,8 +1546,13 @@ void LLGLTFLoader::buildOverrideMatrix(LLJointData& viewer_data, joints_data_map
// then subsctruct them from bind matrix
// Todo: get models that use collision bones, made by different programs
overriden_joint = glm::scale(overriden_joint, viewer_data.mScale);
node.mOverrideRestMatrix = parent_support_rest * overriden_joint;
// <FS:Beq> Match the standard-joint path and preserve the full local
// transform in the propagated rest state.
// overriden_joint = glm::scale(overriden_joint, viewer_data.mScale);
// node.mOverrideRestMatrix = parent_support_rest * overriden_joint;
rest = parent_support_rest * translated_joint;
node.mOverrideRestMatrix = rest;
// </FS:Beq>
}
}
else
@@ -1559,7 +1598,13 @@ glm::mat4 LLGLTFLoader::buildGltfRestMatrix(S32 joint_node_index, const LL::GLTF
if (it != potential_parent.mChildren.end())
{
// Found parent
if (std::find(gltf_skin.mJoints.begin(), gltf_skin.mJoints.end(), joint_node_index) != gltf_skin.mJoints.end())
// <FS:Beq> Recurse only while the parent is also part of the skin
// joint set. The previous test accidentally checked the child node
// again and folded non-joint parents into the reconstructed rest
// chain.
// if (std::find(gltf_skin.mJoints.begin(), gltf_skin.mJoints.end(), joint_node_index) != gltf_skin.mJoints.end())
if (std::find(gltf_skin.mJoints.begin(), gltf_skin.mJoints.end(), static_cast<S32>(i)) != gltf_skin.mJoints.end())
// </FS:Beq>
{
// parent is a joint - recursively combine transform
// assumes that matrix is already valid
@@ -1604,8 +1649,12 @@ glm::mat4 LLGLTFLoader::computeGltfToViewerSkeletonTransform(const joints_data_m
}
// Get the GLTF joint's rest pose (in GLTF coordinate system)
const glm::mat4 &gltf_joint_rest_pose = node_data.mGltfRestMatrix;
glm::mat4 rest_pose = coord_system_rotation * gltf_joint_rest_pose;
// <FS:Beq> Keep the rest-pose conversion consistent with the bind/rest
// construction used above.
// const glm::mat4 &gltf_joint_rest_pose = node_data.mGltfRestMatrix;
// glm::mat4 rest_pose = coord_system_rotation * gltf_joint_rest_pose;
glm::mat4 rest_pose = convert_transform_to_viewer_basis(node_data.mGltfRestMatrix, mApplyXYRotation);
// </FS:Beq>
LL_INFOS("GLTF_DEBUG") << "rest matrix for joint " << joint_name << ": ";