Fix staging buffer required size calculation (fixes bevyengine#1056)

* prepare_uniform_buffers() now computes the required uniform buffer
  size over all assets, rather than just changed ones.

* set_required_staging_buffer_size_to_max() now doesn't overwrite the
  value computed by prepare_uniform_buffers() if the resulting size
  would be smaller.

crates/bevy_render/src/render_graph/nodes/render_resources_node.rs

@@ -216,7 +216,9 @@ where
  }
  }
 
- self.required_staging_buffer_size = new_size;
+ if new_size > self.required_staging_buffer_size {
+ self.required_staging_buffer_size = new_size;
+ }
  }
 
  /// Update the staging buffer to provide enough space to copy data to target buffers.
@@ -687,8 +689,12 @@ fn asset_render_resources_node_system<T: RenderResources + Asset>(
  uniform_buffer_arrays.initialize(asset, render_resource_context);
  }
 
+ for (asset_handle, asset) in assets.iter() {
+ // this computes the required staging buffer size and needs to be performed over all assets,
+ uniform_buffer_arrays.prepare_uniform_buffers(asset_handle, asset);
+ }
+
  for (asset_handle, asset) in changed_assets.iter() {
- uniform_buffer_arrays.prepare_uniform_buffers(*asset_handle, asset);
  let mut bindings =
  asset_render_resource_bindings.get_or_insert_mut(&Handle::<T>::weak(*asset_handle));
  if !setup_uniform_texture_resources::<T>(&asset, render_resource_context, &mut bindings) {