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Add support for loading 1D flex components from OBJ line segments.

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The obj_decoder plugin is updated to parse line segments ('l') from OBJ files and represent them as degenerate triangles. The user_flexcomp compiler now supports flex dimensions of 1, using these parsed line segments to define the 1D flex elements. The compile sample's error reporting is also improved.

PiperOrigin-RevId: 928566870
Change-Id: I6920729d1b1d5aeb391401c3245ebb1d4784c190
This commit is contained in:
Alessio Quaglino
2026-06-08 08:03:04 -07:00
committed by Copybara-Service
parent ac7f198536
commit 7a7dc7ccad
6 changed files with 107 additions and 33 deletions
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plugin/obj_decoder/obj_decoder.cc
+72 -31
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@@ -53,41 +53,80 @@ mjSpec* Decode(mjResource* resource, const mjVFS* vfs) {
std::vector<int> userfacetexcoord;
if (!obj_reader.GetShapes().empty()) {
const auto& obj_mesh = obj_reader.GetShapes()[0].mesh;
const auto& obj_shape = obj_reader.GetShapes()[0];
if (!obj_shape.mesh.indices.empty()) {
const auto& obj_mesh = obj_shape.mesh;
std::vector<tinyobj::index_t> face_indices;
for (size_t face = 0, idx = 0; idx < obj_mesh.indices.size();) {
int nfacevert = obj_mesh.num_face_vertices[face];
if (nfacevert < 3 || nfacevert > 4) {
mju_warning(
"obj_decoder: only tri or quad meshes are supported (file '%s')",
resource->name);
mj_deleteSpec(spec);
return nullptr;
size_t num_face_indices = 0;
for (size_t face = 0; face < obj_mesh.num_face_vertices.size(); ++face) {
int nfacevert = obj_mesh.num_face_vertices[face];
if (nfacevert == 3) {
num_face_indices += 3;
} else if (nfacevert == 4) {
num_face_indices += 6;
}
}
face_indices.push_back(obj_mesh.indices[idx]);
face_indices.push_back(obj_mesh.indices[idx + 1]);
face_indices.push_back(obj_mesh.indices[idx + 2]);
if (nfacevert == 4) {
face_indices.push_back(obj_mesh.indices[idx]);
face_indices.push_back(obj_mesh.indices[idx + 2]);
face_indices.push_back(obj_mesh.indices[idx + 3]);
}
idx += nfacevert;
++face;
}
for (const auto& mesh_index : face_indices) {
userface.push_back(mesh_index.vertex_index);
std::vector<tinyobj::index_t> face_indices;
face_indices.reserve(num_face_indices);
userface.reserve(num_face_indices);
if (!usernormal.empty()) {
userfacenormal.push_back(mesh_index.normal_index);
userfacenormal.reserve(num_face_indices);
}
if (!usertexcoord.empty()) {
userfacetexcoord.reserve(num_face_indices);
}
if (!usertexcoord.empty()) {
userfacetexcoord.push_back(mesh_index.texcoord_index);
for (size_t face = 0, idx = 0; idx < obj_mesh.indices.size();) {
int nfacevert = obj_mesh.num_face_vertices[face];
if (nfacevert < 3 || nfacevert > 4) {
mju_warning(
"obj_decoder: only tri or quad meshes are supported (file '%s')",
resource->name);
mj_deleteSpec(spec);
return nullptr;
}
face_indices.push_back(obj_mesh.indices[idx]);
face_indices.push_back(obj_mesh.indices[idx + 1]);
face_indices.push_back(obj_mesh.indices[idx + 2]);
if (nfacevert == 4) {
face_indices.push_back(obj_mesh.indices[idx]);
face_indices.push_back(obj_mesh.indices[idx + 2]);
face_indices.push_back(obj_mesh.indices[idx + 3]);
}
idx += nfacevert;
++face;
}
for (const auto& mesh_index : face_indices) {
userface.push_back(mesh_index.vertex_index);
if (!usernormal.empty()) {
userfacenormal.push_back(mesh_index.normal_index);
}
if (!usertexcoord.empty()) {
userfacetexcoord.push_back(mesh_index.texcoord_index);
}
}
} else if (!obj_shape.lines.indices.empty()) {
// encode line segments as degenerate triangles (i1, i2, i2) in userface,
// since mjsMesh has no native edge field; decoded back by flexcomp
const auto& obj_lines = obj_shape.lines;
userface.reserve(3 * (obj_lines.indices.size() - obj_lines.num_line_vertices.size()));
size_t idx = 0;
for (size_t l = 0; l < obj_lines.num_line_vertices.size(); l++) {
int nlinevert = obj_lines.num_line_vertices[l];
for (int v = 0; v < nlinevert - 1; v++) {
int i1 = obj_lines.indices[idx + v].vertex_index;
int i2 = obj_lines.indices[idx + v + 1].vertex_index;
userface.push_back(i1);
userface.push_back(i2);
userface.push_back(i2);
}
idx += nlinevert;
}
}
}
@@ -101,8 +140,10 @@ mjSpec* Decode(mjResource* resource, const mjVFS* vfs) {
mjs_setFloat(mesh->usernormal, usernormal.data(), usernormal.size());
mjs_setFloat(mesh->usertexcoord, usertexcoord.data(), usertexcoord.size());
mjs_setInt(mesh->userface, userface.data(), userface.size());
mjs_setInt(mesh->userfacenormal, userfacenormal.data(), userfacenormal.size());
mjs_setInt(mesh->userfacetexcoord, userfacetexcoord.data(), userfacetexcoord.size());
mjs_setInt(mesh->userfacenormal, userfacenormal.data(),
userfacenormal.size());
mjs_setInt(mesh->userfacetexcoord, userfacetexcoord.data(),
userfacetexcoord.size());
return spec;
}