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# Hello World: Populate ovstage and Step

This tutorial shows the smallest end-to-end ovphysx workflow: create an instance, populate an ovstage Stage from USD, attach it, step simulation, and clean up resources. You can use this flow as the starting point for larger integrations.

## Prerequisites

- Prepare a readable USD file for ovstage population.

## Code Language

### Python

Install the package first:

    pip install ovphysx

    import ovphysx
    from ovphysx import PhysX
    from pathlib import Path

    print("Using ovphysx version: ", ovphysx.__version__)

    def attach_scene(physx, usd_path):
        import ovstage

        if not ovstage.population.available():
            raise RuntimeError("ovstage population bridge is unavailable")

        stage = ovstage.Stage("ovphysx-hello-world")
        ordinal = 1
        try:
            ovstage.population.open_usd(stage, str(usd_path), ordinal=ordinal, domains=ovstage.PopulationDomain.PHYSICS)
            physx.attach_ovstage(stage, read_ordinal=ordinal)
            print("Loaded scene through ovstage")
            return stage
        except Exception:
            stage.destroy()
            raise

    script_dir = Path(__file__).resolve().parent
    usd_path = script_dir / ".." / "data" / "links_chain_sample.usda"

    # Initialize PhysX
    physx = PhysX()
    stage = attach_scene(physx, usd_path)

    try:
        # Run a simulation step
        dt = 1.0 / 60.0
        physx.step(dt)
        print("Simulation step completed successfully")
    finally:
        if stage is not None:
            physx.detach_ovstage()
            stage.destroy()
        physx.release()
        print("Cleanup complete")

### C

Download the SDK from the GitHub Releases page and extract it.

CMakeLists.txt

Every C sample uses `find_package(ovphysx)` and links against `ovphysx::ovphysx`. Here is the `CMakeLists.txt` for `hello_world_c`:

    cmake_minimum_required(VERSION 3.16)
    project(HelloWorldC C)

    set(CMAKE_C_STANDARD 11)
    set(CMAKE_C_STANDARD_REQUIRED ON)

    find_package(ovphysx REQUIRED)

    add_executable(hello_world_c main.c)

    # Explicitly set the language to C (not C++)
    set_source_files_properties(main.c PROPERTIES LANGUAGE C)
    set_target_properties(hello_world_c PROPERTIES
        C_STANDARD 11
        C_STANDARD_REQUIRED ON
    )

    # Add compiler-specific flags to enforce strict C compilation
    if(CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
        # GCC/Clang: Add -Werror=implicit-function-declaration to catch C++ leakage
        target_compile_options(hello_world_c PRIVATE
            -Werror=implicit-function-declaration
            -pedantic
        )
    endif()

    if(MSVC)
        # MSVC: Compile as C code explicitly
        target_compile_options(hello_world_c PRIVATE /TC)
    endif()

    target_link_libraries(hello_world_c PRIVATE ovphysx::ovphysx ovphysx::ovstage)
    target_include_directories(hello_world_c PRIVATE "${CMAKE_CURRENT_LIST_DIR}/../common")
    get_filename_component(OVPHYSX_TEST_DATA_DIR "${CMAKE_CURRENT_LIST_DIR}/../../data" ABSOLUTE)
    target_compile_definitions(hello_world_c PRIVATE
        OVPHYSX_TEST_DATA="${OVPHYSX_TEST_DATA_DIR}"
    )
    if(WIN32)
        ovphysx_copy_runtime_dlls(hello_world_c)
    endif()

Build by pointing `CMAKE_PREFIX_PATH` at the installed SDK (refer to SDK Quickstart for details).

Source

    #include "ovphysx/ovphysx.h"
    #include "ovstage_sample.h"
    #include <stdio.h>

    static int run(void)
    {
      // Create PhysX instance with default args
      ovphysx_create_args create_args = OVPHYSX_CREATE_ARGS_DEFAULT;
      ovphysx_handle_t handle = 0;

      ovphysx_result_t result = ovphysx_create_instance(&create_args, &handle);
      if (result.status != OVPHYSX_API_SUCCESS) {
        fprintf(stderr, "Failed to create PhysX instance\n");
      ovphysx_shutdown();
        return 1;
      }

      // Populate ovstage from USD and attach it to ovphysx
      ovphysx_sample_stage_attachment_t stage_attachment = {0};
      if (!ovphysx_sample_attach_usd_with_ovstage(
              handle, OVPHYSX_TEST_DATA "/simple_physics_scene.usda", &stage_attachment)) {
        fprintf(stderr, "Failed to attach ovstage scene\n");
        ovphysx_destroy_instance(handle);
      ovphysx_shutdown();
        return 1;
      }

      // Step the simulation
      ovphysx_enqueue_result_t step_result = ovphysx_step(handle, 0.016f);
      if (step_result.status != OVPHYSX_API_SUCCESS) {
        fprintf(stderr, "Failed to step simulation\n");
        ovphysx_sample_destroy_stage(handle, &stage_attachment);
        ovphysx_destroy_instance(handle);
      ovphysx_shutdown();
        return 1;
      }

      // Wait for step to complete
      ovphysx_op_wait_result_t step_wait_result = {0};
      ovphysx_result_t step_wait_status = ovphysx_wait_op(handle, step_result.op_index, UINT64_MAX, &step_wait_result);
      int step_ok = (step_wait_status.status == OVPHYSX_API_SUCCESS && step_wait_result.num_errors == 0);
      ovphysx_destroy_wait_result(&step_wait_result);
      if (!step_ok) {
        fprintf(stderr, "Simulation step failed\n");
        ovphysx_sample_destroy_stage(handle, &stage_attachment);
        ovphysx_destroy_instance(handle);
      ovphysx_shutdown();
        return 1;
      }

      printf("Simulation step completed successfully\n");

      ovphysx_sample_destroy_stage(handle, &stage_attachment);
      ovphysx_destroy_instance(handle);
      ovphysx_shutdown();
      printf("Cleanup complete\n");

      return 0;
    }

    int main(void) {
        ovphysx_result_t init_r = ovphysx_initialize();
        if (init_r.status != OVPHYSX_API_SUCCESS) {
            fprintf(stderr, "ovphysx_initialize() failed\n");
            return 1;
        }
      int rc = run();
      return rc;
    }

## Result

After this tutorial, you can step the simulation from both Python and C and release all resources cleanly.