Render: support USD Hydra render delegates

Hydra is a rendering architecture part of USD, designed to abstract the
host application from the renderer. A renderer implementing a Hydra
render delegate can run in any host application supporting Hydra, which
now includes Blender.

For external renderers this means less code to be written, and improved
performance due to a using a C++ API instead of a Python API.

Add-ons need to subclass bpy.types.HydraRenderEngine. See the example in
the Python API docs for details.

An add-on for Hydra Storm will be included as well. This is USD's
rasterizing renderer, used in other applications like usdview. For users
it can provide a preview of USD file export, and for developers it
serves a reference.

There are still limitations and missing features, especially around
materials. The remaining to do items are tracked in #110765.

This feature was contributed by AMD.

Ref #110765

Co-authored-by: Georgiy Markelov <georgiy.m.markelov@gmail.com>
Co-authored-by: Vasyl-Pidhirskyi <vpidhirskyi@gmail.com>
Co-authored-by: Brian Savery <brian.savery@gmail.com>
Co-authored-by: Brecht Van Lommel <brecht@blender.org>

Pull Request: https://projects.blender.org/blender/blender/pulls/104712

scripts/modules/bpy_types.py

@@ -938,10 +938,6 @@ class PropertyGroup(StructRNA, metaclass=RNAMetaPropGroup):
     __slots__ = ()
 
 
-class RenderEngine(StructRNA, metaclass=RNAMeta):
-    __slots__ = ()
-
-
 class KeyingSetInfo(StructRNA, metaclass=RNAMeta):
     __slots__ = ()
 
@@ -1256,3 +1252,71 @@ class GeometryNode(NodeInternal):
     @classmethod
     def poll(cls, ntree):
         return ntree.bl_idname == 'GeometryNodeTree'
+
+
+class RenderEngine(StructRNA, metaclass=RNAMeta):
+    __slots__ = ()
+
+
+class HydraRenderEngine(RenderEngine):
+    __slots__ = ()
+
+    bl_use_shading_nodes_custom = False
+    bl_delegate_id = 'HdStormRendererPlugin'
+
+    def __init__(self):
+        self.engine_ptr = None
+
+    def __del__(self):
+        if hasattr(self, 'engine_ptr'):
+            if self.engine_ptr:
+                import _bpy_hydra
+                _bpy_hydra.engine_free(self.engine_ptr)
+
+    def get_render_settings(self, engine_type: str):
+        """
+        Provide render settings for `HdRenderDelegate`.
+        """
+        return {}
+
+    # Final render.
+    def update(self, data, depsgraph):
+        import _bpy_hydra
+
+        engine_type = 'PREVIEW' if self.is_preview else 'FINAL'
+        if not self.engine_ptr:
+            self.engine_ptr = _bpy_hydra.engine_create(self, engine_type, self.bl_delegate_id)
+        if not self.engine_ptr:
+            return
+
+        _bpy_hydra.engine_update(self.engine_ptr, depsgraph, None)
+
+        for key, val in self.get_render_settings('PREVIEW' if self.is_preview else 'FINAL').items():
+            _bpy_hydra.engine_set_render_setting(self.engine_ptr, key, val)
+
+    def render(self, depsgraph):
+        if not self.engine_ptr:
+            return
+
+        import _bpy_hydra
+        _bpy_hydra.engine_render(self.engine_ptr)
+
+    # Viewport render.
+    def view_update(self, context, depsgraph):
+        import _bpy_hydra
+        if not self.engine_ptr:
+            self.engine_ptr = _bpy_hydra.engine_create(self, 'VIEWPORT', self.bl_delegate_id)
+        if not self.engine_ptr:
+            return
+
+        _bpy_hydra.engine_update(self.engine_ptr, depsgraph, context)
+
+        for key, val in self.get_render_settings('VIEWPORT').items():
+            _bpy_hydra.engine_set_render_setting(self.engine_ptr, key, val)
+
+    def view_draw(self, context, depsgraph):
+        if not self.engine_ptr:
+            return
+
+        import _bpy_hydra
+        _bpy_hydra.engine_view_draw(self.engine_ptr, context)