# Copyright (C) 2020-2025 Motphys Technology Co., Ltd. All Rights Reserved. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. # ============================================================================== """ Gravity Direction Randomization in a Transparent Box This example demonstrates per-instance gravity override by placing a small ball at the center of a transparent six-sided box and assigning each batch instance a different gravity direction. Physical intuition: - The six translucent walls form a closed box. - A small sphere starts near the center of each box. - Every batch instance uses the same model, but a different Data-only gravity vector. - The ball accelerates toward a different wall in each instance, showing that gravity direction is randomized per SceneData instance rather than by changing the shared Model options. Key concepts: - Scene-level gravity override with ``model.set_gravity_override(data, gravity)`` - Batch simulation to compare multiple gravity directions simultaneously Mouse controls: - Press and hold left button then drag to rotate the camera/view - Press and hold right button then drag to pan/translate the view """ import numpy as np from motrixsim import SceneData, load_mjcf_str from motrixsim.render import RenderApp, RenderSettings MJCF = """ """ BATCH = 16 GRAVITY_MAGNITUDE = 6.0 def random_unit_vectors(rng: np.random.Generator, count: int) -> np.ndarray: vectors = rng.normal(size=(count, 3)).astype(np.float32) vectors /= np.linalg.norm(vectors, axis=1, keepdims=True) return vectors def main(): with RenderApp() as render: model = load_mjcf_str(MJCF) render_offset = [] for i in range(4): for j in range(4): render_offset.append([-i * 3.0, j * 3.0, 0]) render_settings = RenderSettings(False, True, True, True, True) render.launch( model, batch=BATCH, render_offset=render_offset, render_settings=render_settings, ) render.system_camera.set_view( lookat=[-4.5, 4.5, 0.0], distance=18.0, elevation=-35.0, azimuth=45.0, ) data = SceneData(model, batch=(BATCH,)) rng = np.random.default_rng(7) directions = random_unit_vectors(rng, BATCH) gravity = (directions * GRAVITY_MAGNITUDE).astype(np.float32) model.set_gravity_override(data, gravity) print("\n" + "=" * 72) print("Gravity Direction Randomization") print("=" * 72) for i, g in enumerate(gravity): print(f" Instance {i:2d}: gravity = [{g[0]: .2f}, {g[1]: .2f}, {g[2]: .2f}]") print("=" * 72 + "\n") while not render.is_closed: model.step(data) render.sync(data) if __name__ == "__main__": main()