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When parsing USD, infer gravity from stage metadata if UsdPhysicsScene missing or undefined.

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PiperOrigin-RevId: 813705210
Change-Id: I13741af6dc87ecd9efb83219e978f5f06c72d021
This commit is contained in:
Sam Haves
2025-10-01 05:18:28 -07:00
committed by Copybara-Service
parent b1ae44d10f
commit c439628f82
1 changed files with 50 additions and 10 deletions
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src/experimental/usd/usd_to_mjspec.cc
+50 -10
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@@ -16,6 +16,7 @@
#include <cstddef>
#include <map>
#include <memory>
#include <optional>
#include <string>
#include <vector>
@@ -51,6 +52,7 @@
#include <pxr/usd/usdGeom/cylinder.h>
#include <pxr/usd/usdGeom/gprim.h>
#include <pxr/usd/usdGeom/mesh.h>
#include <pxr/usd/usdGeom/metrics.h>
#include <pxr/usd/usdGeom/plane.h>
#include <pxr/usd/usdGeom/primvar.h>
#include <pxr/usd/usdGeom/primvarsAPI.h>
@@ -383,20 +385,55 @@ mjsMesh* ParseUsdMesh(mjSpec* spec, const pxr::UsdPrim& prim, mjsGeom* geom,
return mesh;
}
void SetGravityAttributes(
mjSpec* spec, const pxr::UsdStageRefPtr stage,
std::optional<pxr::GfVec3f> gravity_direction = std::nullopt,
std::optional<float> gravity_magnitude = std::nullopt) {
// Parse gravity and gravity direction.
if (!gravity_direction.has_value()) {
TfToken up_axis = pxr::UsdGeomGetStageUpAxis(stage);
if (up_axis == pxr::UsdGeomTokens->y) {
gravity_direction = pxr::GfVec3f(0, -1, 0);
} else if (up_axis == pxr::UsdGeomTokens->z) {
gravity_direction = pxr::GfVec3f(0, 0, -1);
} else {
mju_error("Invalid stage up axis token %s", up_axis.GetString().c_str());
}
}
if (!gravity_magnitude.has_value()) {
gravity_magnitude = 9.81f / pxr::UsdGeomGetStageMetersPerUnit(stage);
}
pxr::GfVec3f gravity = gravity_direction.value() * gravity_magnitude.value();
spec->option.gravity[0] = gravity[0];
spec->option.gravity[1] = gravity[1];
spec->option.gravity[2] = gravity[2];
}
void ParseUsdPhysicsScene(mjSpec* spec,
const pxr::UsdPhysicsScene& physics_scene) {
std::optional<pxr::GfVec3f> gravity_direction = std::nullopt;
std::optional<float> gravity_magnitude = std::nullopt;
auto stage = physics_scene.GetPrim().GetStage();
// Parse gravity and gravity direction.
pxr::GfVec3f gravity_direction;
physics_scene.GetGravityDirectionAttr().Get(&gravity_direction);
auto gravity_direction_attr = physics_scene.GetGravityDirectionAttr();
if (gravity_direction_attr.HasAuthoredValue()) {
pxr::GfVec3f authored_gravity_dir;
gravity_direction_attr.Get(&authored_gravity_dir);
gravity_direction = authored_gravity_dir;
}
float gravity_magnitude;
physics_scene.GetGravityMagnitudeAttr().Get(&gravity_magnitude);
auto gravity_magnitude_attr = physics_scene.GetGravityMagnitudeAttr();
if (gravity_magnitude_attr.HasAuthoredValue()) {
float authored_gravity_magnitude;
gravity_magnitude_attr.Get(&authored_gravity_magnitude);
gravity_magnitude = authored_gravity_magnitude;
}
gravity_direction *= gravity_magnitude;
spec->option.gravity[0] = gravity_direction[0];
spec->option.gravity[1] = gravity_direction[1];
spec->option.gravity[2] = gravity_direction[2];
SetGravityAttributes(spec, stage, gravity_direction, gravity_magnitude);
// Early exit if theres no MjcPhysicsSceneAPI applied.
if (!physics_scene.GetPrim().HasAPI<pxr::MjcPhysicsSceneAPI>()) {
@@ -1724,6 +1761,10 @@ mjSpec* mj_parseUSDStage(const pxr::UsdStageRefPtr stage) {
if (!root->physics_scene.IsEmpty()) {
mujoco::usd::ParseUsdPhysicsScene(
spec, pxr::UsdPhysicsScene::Get(stage, root->physics_scene));
} else {
// If there is no physics scene we still need to infer the gravity vector
// from the stage up axis and units per meter metadata.
mujoco::usd::SetGravityAttributes(spec, stage);
}
if (!root->keyframes.empty()) {
@@ -1754,4 +1795,3 @@ MJAPI mjSpec* mj_parseUSD(const char* identifier, const mjVFS* vfs, char* error,
auto stage = pxr::UsdStage::Open(identifier);
return mj_parseUSDStage(stage);
}