[FEATURE] Enabling rasterizer camera sensor to work with n_envs > 1.

[Narsil]

Description

This reallows RasterizerCameraSensor to work with n_envs > 1.

The PyRenderer requires env_separate_rigid=True to correctly separate the rendering.
This requires OpenGL 4.2 which is not available on Metal.

I moved the errorring out to the .build() since I think it's easier on users to have errors earlier rather than later.

I chose not to change the batched dimension on the Rasterizer (it can return a non batched variant when use_separate_rigid=False) to minimize the surface of this change.

Diff unfortunately includes some ruff format modifications, not reverted automatically by black.
I can manually revert if necessary.

Motivation and Context

It's important to have rendering when using n_envs>1 in the context of leveraging the batched simulation.
This version works, even if not optimal compared to a purely batched rendering.

I decided to not change other renderers as they belong in other PRs IMHO.

Screenshots (if appropriate):

https://huggingface.co/datasets/Genesis-Intelligence/snapshots/commit/1029f0b5ec874b93dc5170179f7f5a3e770b10ea

Checklist:

• I read the CONTRIBUTING document.
• I followed the Submitting Code Changes section of CONTRIBUTING document.
• I tagged the title correctly (including BUG FIX/FEATURE/MISC/BREAKING)
• I updated the documentation accordingly or no change is needed.
• I tested my changes and added instructions on how to test it for reviewers.
• I have added tests to cover my changes.
• All new and existing tests passed.

[duburcqa]

Diff unfortunately includes some ruff format modifications, not reverted automatically by black.
I can manually revert if necessary.

Yes, that would be great indeed.

[duburcqa]

You should probably also apply this patch:

diff --git a/genesis/ext/pyrender/jit_render.py b/genesis/ext/pyrender/jit_render.py
index e163af05..beacb87c 100644
--- a/genesis/ext/pyrender/jit_render.py
+++ b/genesis/ext/pyrender/jit_render.py
@@ -374,7 +374,7 @@ class JITRenderer:
         self.gl = GLWrapper()

         IS_OPENGL_42_AVAILABLE = hasattr(self.gl.wrapper_instance, "glDrawElementsInstancedBaseInstance")
-        OPENGL_42_ERROR_MSG = "Seperated env rendering not supported because OpenGL 4.2 not available on this machine."
+        OPENGL_42_ERROR_MSG = "Separated env rendering not supported because OpenGL 4.2 not available on this machine."

         @nb.jit(
             nb.none(
diff --git a/genesis/ext/pyrender/renderer.py b/genesis/ext/pyrender/renderer.py
index 4f72e509..a3d7c2ed 100644
--- a/genesis/ext/pyrender/renderer.py
+++ b/genesis/ext/pyrender/renderer.py
@@ -152,7 +152,7 @@ class Renderer(object):

         if flags & RenderFlags.ENV_SEPARATE and flags & RenderFlags.OFFSCREEN:
             n_envs = scene.n_envs
-            use_env_idx = True
+            use_env_idx = True and scene.n_envs > 1
         else:
             n_envs = 1
             use_env_idx = False
diff --git a/genesis/vis/camera.py b/genesis/vis/camera.py
index c1fb8bfb..32cedefa 100644
--- a/genesis/vis/camera.py
+++ b/genesis/vis/camera.py
@@ -156,7 +156,7 @@ class Camera(RBC):
                 self._raytracer.add_camera(self)
             else:
                 self._is_batched = False
-                if self._visualizer.scene.n_envs > 0 and self._visualizer._context.env_separate_rigid:
+                if self._visualizer.scene.n_envs > 1 and self._visualizer._context.env_separate_rigid:
                     gs.logger.warning(
                         "Batched rendering via 'VisOptions.env_separate_rigid=True' is only partially supported by "
                         "Rasterizer for now. The same camera transform will be used for all the environments."
@@ -165,7 +165,7 @@ class Camera(RBC):
                 if self._env_idx is None:
                     if not self._is_batched:
                         self._env_idx = int(self._visualizer._context.rendered_envs_idx[0])
-                        if self._visualizer.scene.n_envs > 0:
+                        if self._visualizer.scene.n_envs > 1:
                             gs.logger.info(
                                 "Raytracer and Rasterizer requires binding to the camera with a specific environment "
                                 "index. Defaulting to 'rendered_envs_idx[0]'. Please specify 'env_idx' if necessary."

[Narsil]

What does use_env_idx mean. I've seen it in the code, but I dont' really understand its purpose...

[duburcqa]

What does use_env_idx mean. I've seen it in the code, but I dont' really understand its purpose...

use_env_idx is an internal flag of pyrender to determine whether it should filter "geometries" based on env idx (which requires OpenGL>4.2) and just consider all of them no matter what.